effect of hydrodynamic characteristics on flotation

EFFECT OF HYDRODYNAMIC

CHARACTERISTICS ON FLOTATION

TREATMENT PROCESS OF OILY

WASTEWATER

A Thesis

Submitted to the

Department of Chemical Engineering at the University of

Technology in Partial Fulfillment of the Requirements for the

Degree of Master of Science in Chemical Engineering / Refining

Oil&Gas

By

Shahad Salim Mohammed (B.Sc. in Chemical Engineering, 2009)

2012

Ministry of Higher Education

& Scientific Research

University of Technology

Chemical Engineering Department

Acknowledgements

My thanks go to Allah for his mercy and blessing.

I wish to express my sincere gratitude and grateful admiration to my

supervisor Prof. Dr. Thamer J.Mohammed, for choosing the research and for

his continuous guidance, efforts and interest, which contributed to the

completion of the present work.

Also, I wish to express my respectful regard to the Chemical

Engineering Department, University of Technology, where this research was

conducted for providing financial and logistic facilities.

My respectful regard goes to the staff of Petroleum Research

and Development Center especially Mr. Zaidoon khalaf and Miss Nahla

namir for their assistance and help during the experimental work.

My deepest thanks are given to my family for their support

and encouragement throughout this endeavor.

My very deep respect and sincere appreciation go to my

Father (May Allah have Mercy on his soul) whose memory

encouraged and gave me so much hope and support.

Also, I would like to express my deep gratitude to my friends

for their support and encouragement.

Shahad

I

V

EFFECT OF HYDRODYNAMIC CHARACTERISTICS ON FLOTATION TREATMENT

PROCESS OF OILY WASTEWATER

B y Shahad Salim Mohammed

Supervised by

Prof.Dr.Thamer J.Mohammed

In the North Oil Company (Kirkuk) which represents one of the important

companies in Iraq that consumes a large quantity of water, the oily wastewater

discharges from this company represent a great threat to the agricultural lands.

The aim of the present work is to select the efficient systems for treating oily

wastewater using different flotation techniques. Two flotation techniques were

carried out: Induced Air Flotation (IAF), and Modified Induced Air Flotation

(MIAF) with a coagulation processes.

The experimental work was carried out using flotation bubble column of

Perspex glass (10cm I.D, 150cm height). A liquid depth of 70cm was kept

constant throughout the study. Different two types of gas distributors namely

Perspex perforated plate of diameter of 0.002m was drilled with (70) holes and

the second one is a porous ceramic plate of 0.09m diameter with pore size

(120µm). In order to achieve effective mixing and to modify the flotation

column (MIAF), stirrer was used with a rotational speed of (50-250) rpm. A

monometer was used to measure the local gas hold up; also a high speed camera

was used to measure the bubble rise velocity and bubble size.

AbstractAbstractAbstractAbstract

VI

The variables that affects the removal efficiency (R%) of oil from

wastewater is hydrodynamic characteristics, such as gas velocities (0.00636-

0.0636) m/sec, oil concentration (30-800) ppm, surfactant concentration(SLS,

Camper) and the addition of alum, pH (4.3-8.5), speed of stirrer (50-250) rpm,

have been studied.

The study has showed that the removal efficiency of oil, COD and BOD

were related to the additive dose of Alum and SLS. It was found that the flotation

rate increases when using alum and surfactant together, the fastest removal rate

was obtained when pH 4.3 and also, when a stirrer speed 200 rpm was used, the

removal efficiency was about 98%(residual oil <10 ppm) when the initial oil

concentration was 800 ppm.

The kinetics of flotation bubble column was studied and it was found that the

removal rate constant increases with increasing oil concentration and with dosage

of surfactant (SLS). The results showed that the order of the kinetics flotation

process changes between half to first order.

The interfacial area (a) obtained experimentally from the bubble

hydrodynamic parameters and the velocity gradient (G), have been proven to be

important parameters for controlling the flotation process efficiency.

The experimental results of the removal efficiency are represented in two and

three dimensional graphs. An empirical correlation for gas hold up using MIAF

has been developed as follows:

εg =0.39 (Ug) 0.0163 (H/D) 0.157 (N/ρL) 0.473

Statistical analysis showed that the average absolute error and correlation

coefficient are 2% and 0.98 respectively. And general correlation for the removal

efficiency (R %) using dimensionless groups was found to be:

R% = 1.67 (CA/ ρl )145.7 (CS/ρL)161 (C/Co)

0.0624(1/Re)1.48(1/We)1.54 (1/Fr)1.096

VII

The correlation obtained gave an average absolute error and correlation

coefficient 0.053%, 0.9999 respectively.

XV

Subject page Acknowledgement I

Abstract V

Nomenclature X

Greek Symbols XII

List of Figures XIV

List of Tables XIX

Contents XV

Chapter one: Introduction 1.1 General 1

1.2. Oily Wastewater Treatment Technologies 2

1.2.1 Flotation 4

1.2.1.1 Flotation Column 4

1.3 Pollutants Effect 7

1.4 Case Study 8

1.5 The aim of the present work 8

Chapter two: Literature survey 2.1 Introduction 10

2.2. Hydrodynamic parameter affecting removal efficiency 10

2.2.1 .Gas Hold up 10

2.2.2. Effect of the flow rate 12

2.3. Operating condition affecting removal efficiency 13

2.3.1. Effect of temperature

13

2.3.2. Effect of pH 15

2.4. Geometrical Dimensions 17 2.4.1. Effect of Bubble Diameter and (H/d) Ratio on Removal efficiency

17

2.4.2. Effect of Sparger Type 18

2.5. The Effect of Surfactant and Additives on Removal Efficiency 20

Contents

XVI

2.6. Hybrid Treatment (Coagulation –Flocculation-Flotation) 23

2.7. Empirical Equations of Parameters 26

2.7.1. Bubble rise velocity 26

2.7.2. Bubble Size 29

2.7.3. Gas Hold up 30 2.7.4. Removal Efficiency 32 2.8 Summary: 34

Chapter three: Experimental work 3.1. Introduction 35

3.2. Characteristic and Preparation of Sample Wastewater 35

3.3. Materials 36

3.4. Experimental Set up 37

3.41. Flotation column 37

3.4.2. Gas Delivery 38

3.4.3. Experimental Procedure 38

3.5 Determination of Oil Concentration 42

3.5.1. Outline of the Method 42

3.5.2 Calibration 43

3.5.4 Procedure 43 3.6. Bubble Size and Rise Velocity Measurement 43

3.7. Sample wastewater treatment 45

Chapter four: Theoretical concepts 4.1. Determination of Rate Constant 46

4.2 Froth height equation 48

4.3 Dimensional Analyses 49

Chapter five: Results and discussion Introduction 50

5.1 Hydrodynamic Characteristics 50

5.1.1 Bubble Diameter 50

5.1.2 Bubble Rise Velocity 51

5.1.3 Gas Hold-up 52

XVII

5.2 Effect of Various Factors on the Removal Efficacy of Oily Wastewater 61

5.2.1 Effect of pH 61

5.2.2 Effect of Initial Oil Concentration 62

5.2.3 Effect of Gas Velocities on the Removal Efficiency 63

5.2.4 Effect of Coagulant and Flocculant Agents 63

5.2.5 Effect of Sampling Zone 65

5.2.6. Effect of Mixing 66

5.3 Effect of Interfacial Area and Velocity Gradient on the

Removal Efficiency 81

5.4. The Best Conditions 84

5.5. Dimensionless Groups for Removal Efficiency 86

Chapter six: Conclusions and Recommendations for

future work

6.1. Conclusions 88 6.1.1 Separation of Oil 88

6.2. Recommendations for future work 89

References 90

Appendices

Appendix A: Calibration curve of rotameter 102

Appendix B: Calibration curve of mixer 103

Appendix C distributor design 104

Appendix D Sample of calculations 107

Appendix E Tables figures 110

X

Nomenclature

Units Definition Symbol

(m2) Specific surface area of column A

(N/m2) Atmosphere Atm

(-) American petroleum institute API

(-) Bond number

gd lR

2

Bo

(ppm) Chemical oxygen demand COD

(-) Corrugate plate inceptor CPI

(-) Drag coefficient DC

(ppm) Alum concentration CA

(ppm) Surfactant concentration CS

(ppm) Oil concentration C

(m) Initial oil concentration CO

(ppm) Chemical Oxygen Demand in the under flow in

eq.2.22 (COD)U

(ppm) Chemical Oxygen Demand in the feed flow in

eq.2.22 (COD)L

(-) Dissolved gas flotation DGF

(m) Column diameter in eq.217 and 2.18 Dc, D

(m) Bubble diameter bd

(-) Environmental protection agency EPA

(-) Froude number

R

g

gd

V Fr

(sec-1

) Frequency of bubble FB

2sm Gravitational acceleration g

(sec-1

) Mean velocity gradient G

(-) Galileo number 2

3

L

lR gd

Ga

(m) Bed height H, h

(m)

Froth height hf

XI

NTU Naphlometric turbidity unit (-)

N Speed of the stirrer (sec-1

)

Nb Number of bubble (-)

PPI Parallel plate inceptor (-)

ppm Part per million (-)

P Power in the column W

PPI Parallel plate inceptor

Q Gas flow rate (m3/min)

Qair/Ql Air flow rate/feed flow rate (-)

Qa/Qis feed flow rate/saturated liquid rate (-)

Re Reynolds number

Ud (-)

Rg Gas constant = 8.314 Kmol

mPa

*

* 3

R Removal efficiency (1-C/Co)*100 (-)

SF Scale correction factor (-)

Sb Surface area of the bubble (m2)

t Time (sec)

TTW Treated waste transmittance (%) (-)

TWF Waste feed transmittance (%) (-)

TW Water transmittance (%) (-)

Ugs Bubble rise velocity in eq.(2.9) &(2.13) (m/sec)

U Fluid velocity in Table (2.1) (m/sec)

Ug Gas velocity (m/sec)

tU Terminal velocity in Table (2.1) (m/sec)

Vb Total volume of the bubble (m3)

We Weeper number l Ug2d/ (-)

(-) Induced air flotation IAF, IGF

(m/sec) superficial gas velocity in eq.2.10 Jg

(m/sec) superficial liquid velocity in eq.2.10 Jl

(sec-1

) Rate constant k

(-) Modified induced air flotation MAIF

XII

Symbol Definition Units

Micron (-)

l Density of the liquid (kg/m3)

g Density of the gas (kg/m3)

w The density of water (kg/m3)

l Liquid viscosity (Pa.s)

g Gas viscosity (Pa.s)

gv Superficial gas velocity in Table (2.1) (m/sec)

Surface tension (m

N )

g Volume fraction of gas or gas holdup (-)

bv Bubble rise velocity in Table (2.1) (m/s)

w Viscosity of water (Pa.s) Density of liquid (kg/m

3)

tP Pressure difference along the column (atm)

z Liquid height in the manometer

(m)

Greek Symbols

Chapter One

1.1. General

Oil contaminated wastewater has been recognized as one of the most

concerned pollution sources. This kind of wastewater comes from variety of

sources such as crude oil production, oil refinery, compressor, condensates,

lubricant and cooling agents and car washing. The oily wastewater is considered as

hazardous industrial wastewater because it contains toxic substances such as

phenols, petroleum, hydrocarbons, and poly aromatic hydrocarbons; therefore the

treatment of oily wastewater is particularly difficult, especially when oil is found at

low concentration in the water phase (Phan, 2002, and Couto&Massrani, 2005).

The type of oil-water mixture may be classified as oil and present,

as free oil, grease, dispersed oil, emulsified oil or dissolved oil. Free oil is usually

characterized by an oil-water mixture with droplets greater than or equal to

(150m) in size (API, 1969). While a dispersed oil mixture has a droplet size

range between (20-150m), and the emulsified oil mixture will have droplet

size smaller than(20m) (Francis &Eric 1983). A wastewater with an oil-water

mixture where the oil is said to be soluble is a liquid where oil is not present in the

form of droplets the oil particle size would be typically less than (5m) (Patterson,

1985). Free oil is not dispersed and float on the surface, the oily layer can be

skimmed. Soluble oil requires the use of ion-exchange technology (Zoubolils

&Arranas, 2000). Carbon adsorption or membrane filtration treatment is very

effective to remove emulsified oil (Wemco, 1982). Non-emulsified dispersed oil

can be removed by gravity separation, e.g. hydro cyclones, gravity filter or

sedimentation or flotation where oily droplets larger than 40 are removed by

Introduction

*Chapter one: Introduction 2

flotation techniques(Zoubolils&Arranas,2000) . Chemical pretreatment is very

important in this treatment. Chemical treatment to inactivate the emulsifying

substances, this inactivation may be accomplished by the use of chemical

coagulating agents such as aluminum salts, ferric salts, and calcium salts. The

use of organic poly electrolytes is also widely recognized as a practical and

often efficient technique (Zuber &Hench, 1962). The process of bringing together

the destabilized or "coagulated" particles to form a larger agglomeration of flocc

by physical mixing that is called flocculation (Koide et al, 1979). (NSF, 1999)

states that the flocculation is the process to enhance agglomeration or collection of

smaller floc particles into larger, more easily stable particles through gentle stirring

by hydraulic or mechanical means.

1.2. Oily Wastewater Treatment Technologies

Treatment methods for oily wastewater can be classified into three categories

namely, primary or gravity treatment units, secondary processes and tertiary

processes (Fig.1.1). However the applications of each of these technologies depend

on the quality characteristics and condition of the particular oil-water mixture.

Table 1.1 shows the main advantages and disadvantages for each system (Jorge et

al, 2007).


Table (1.1): The advantage and disadvantage of the treatment process (Jorge et al., 2007).

Disadvantage Advantage Process Limited in removal of

emulsion particles

Effective in removal of

free and dispersed oil

,simple and economical

API,CPI, PPI Gravitational

separators

Generates mud

management when using

coagulants

Effective for the removal

of dispersed and

emulsified oil in range of

1000 to 100 ppm, in

general reliable

DGF,IGF flotation

Requires very stable

operating conditions ,high

energy consumption

Possible to attain a great

separation with initial

concentration up to 2000

ppm

Static and dynamic hydro-

cyclones

Not competitive with other

technologies when smaller

size than 15m, due to

high maintenance energy

costs

Effective for removal

emulsified oil in range of 3

to 7 m

Centrifugal

Pretreatment required ,the

regeneration or change of

medium may create

disposal problems, its

operation is very varied

Effective for removal

emulsified oil that

dispersed in range greater

than 2 m

Sand filtration,

anthracite, vegetable

means, multiple beds

Very low activity ratio (0.1

g oil/g CA), requires high

regeneration or changes

,limited to loads greater

than 100 ppm, not for high

flow because of high

maintenance

Effective for removal of

all types of particles ,even

those oil soluble ones

Carbon activated

Useful in specific cases,

low flow ,short-lived with

emulsions ,requires very

effective pretreatment

Effective for removal of

soluble oil

Membrane processes ,

inverse osmosis ,ultra,

micro and nano filtration


Figure(1.1): Oil/water emulsion conventional systems (Degremont, 1979)

The oil/water emulsion cannot be removed by simple gravity separation;

therefore a variety of secondary and tertiary treatment methods have been applied

to treat the soluble fraction and the oil/water emulsion of the oily wastewater.

Among the physical-chemical processes, flotation system is one of the most

common processes used to treat the oily wastewater after gravity separation. This

process has been reported to achieve oil removal of 80% to 90% (ASTM, 1969,

Donal, 1987 & Meyers, 1987).

1.2.1 Flotation:

Flotation is an alternative as it has high efficiency as well as low

operating cost(Rubio et al,2002). Flotation separation is a process used in many


industries to separate one constituent from another (Arther, 2006). The use of

flotation has a great potential owing to high throughput and efficiency of modern

equipment (Zabel, 1992). The general process of flotation separation can be divided

into two types, dispersed and dissolved air flotation (Arther, 2006).

In dissolved air flotation technique the bubbles are formed by nucleation on

the particles. In this technique a substantial portion of the clarified effluent must be

recycled, compressed to 4 up to 5atm and saturated with air. In dispersed air

flotation air bubble are generated either by electrolysis or by forcing air

through, porous glass, single orifice or other suitable sparger. In this type of

flotation the gas flow rate may be an important operating variable. Dispersed air

has the advantage of eliminating the need for recycling (Radoev et al, 1989).

1.2.1.1 Flotation Column:

In order to appreciate the need for a fundamentally based dynamic model

of column flotation, it is first necessary to understand the behavior of flotation

columns . In general the appearance of flotation columns was the result of a

novel idea in the 1960's aimed at improving the performance of conventional

flotation significant. Gain achieved with flotation columns over conventional

flotation technology include:

Higher grades

Lower operating costs

Improved operating stability

Reduced maintenance requirements

Increased suitability for automatic control (wheeler et al, 1966)


Most flotation columns are characterized by a series of features, illustrated in

Fig.1.2.

Figure (1.2): Flotation Column Layout (Gu et al, 1999).

That include:

Higher height to diameter ratio.

Wash water sprinkle at the same point below the over flow lip.

Feed addition point located at an intermediate location along the

column height.

Bubble generation system at the bottom of column.

No mechanism of agitation (Caixeta et al, 2000)

Main applications have been in the removal of solids, ions, macromolecules

and fibers, and other materials from water (Saxena, 1989) more, flotation is also

practiced in other fields (Kumar et al, 1976) such as:

Analytical chemistry

Protein separation

Treatment of spent photography liquors

Odor removal


Plastics separation and recycling

Deinking of printed paper

Separation of micro-organisms

Removal of sulfur dyes resins and rubber, impurities in cane sugar

Clarification of fruit juices.

1.3 Pollutants Effect

The world is faced with problems related to the management of wastewater.

This is due to extensive industrialization, increasing population density and high

urbanized societies were the major sources of the natural water pollution load. This

is a great burden in terms of wastewater management effluents generated from

domestic and industrial activities constitute and can consequently lead to a point-

source pollution problem, the polluted water discharge from the refineries that

contain pollutants and its environmental effects are shown in Table 1.2.

Table (1.2): Components of Wastewater (Henze et al, 1997)

Environmental effect Of special interest Component

Risk when bathing and eating

shellfish

Pathogenic bacteria, virus

and worms eggs

Micro-organisms

Oxygen depletion in rivers,

Lakes and estuaries.

Biodegradable organic

materials

Toxic effect, aesthetic

inconveniences, bio

accumulation

Detergents, pesticides, fats,

oil and grease, coloring,

solvents, phenol, cyanide

Other organic materials

Oxygen Depletion, toxic effect. Nitrogen, phosphorus,

ammonia

Nutrients

Toxic effect, bio accumulation Hg, Pb, Cd, Cr, Cu, Ni Metals

Corrosion, toxic effect Acids, e.g. hydrogen

sulphide, bases

Other inorganic

materials

Changing living conditions for

flora and fauna

Hot water Thermal effects

Aesthetic inconveniences, toxic

effect

Hydrogen sulphide Odor (and taste)


1.4 Case Study

This research is concerned with the problem which takes place in the North

Oil Company, where the oil is mixed with water in different locations as shown in

Fig.1.3, especially thought-out cooling systems where the water is used to cool the

equipments and where there are some leakage in the pipes and other equipments,

so the water becomes polluted.

This problem is tried to be solved by the application of flotation treatment

process before the wastewater discharge to river and agricultural lands with

allowable limit concentration (<10 ppm), depending on EPA and Environmental

Specification of Iraq, (Iraqi regulation, 2001).

1.5 The aim of the present work

1- To investigate the possibility and efficiency of flotation treatment process of

oily wastewater in North Oil Company.

2- To study the hydrodynamic characteristic of flotation column with air

bubble.

3- To study the effect of different parameters of hydrodynamic characteristic

(gas hold up, bubble size, gas velocity…etc) in flotation bubble column on

removal efficiency of oil.

4- To study the effects of various variables on the removal efficiency such as,

oil concentration, different type of surfactant concentration, pH and addition

of alum as a coagulant flocculent.

5- To select the best surfactant type as a demulsified substance of oily

wastewater.

6- To study the kinetic of flotation column of emulsified oil wastewater.

7- To find the model to correlate different parameters which affects the

removal efficiency of oil from wastewater.


Oily wastewater

tank (slop tank)

The main

water tank

Rounded

tank to receive

untreated

crude oilCrude oil treatment unit to

remove the hydrogen

sulphide and other light

gases

Export tanks

Cooling tower

for industrial

water

Treatment unit

of boiler water Boiler API-

separator

Treated oil consistent with

standard specifications

Treated oil

Oily wastewater

Oil

y w

ast

ew

ate

r

Oil

y w

ast

ew

ate

r

To different users

To f

ire s

yst

em

and

hum

an u

se

Steam

Lagoon

Oily

wastewater

Wast

ew

ate

r

blo

w d

ow

n

Water flows down from cooling tower

to reduce total dissolved solid contents

Water flows down from action process

treatment unit and flows down from boiler

Feed

waterWater

Untreated crude oil

from pump station

Compressing gas

station

Fire pit

Gases liberated from

treatment process

To agricultural

lands

Cooling water content

anticorrosion and antiscale

Fig. 1.3 New Process Plant in the North Oil Company

Chapter two

2.1. Introduction

Most of the research studies on the separation of oil from wastewater

have addressed the effect of oil concentration, type and concentration of

destabilizing agent for oil-water emulsion technique to be employed. In this

chapter the hydrodynamic characteristics of flotation column that affect the oil

removal efficiency was classified and the previous studies are shown for each

one, these studies were published in different international journals, text books

and websites, and papers published locally in resent years.

2.2. Hydrodynamic Parameters Affecting Removal Efficiency

2.2.1 .Gas Hold up

Gas hold up is a dimensionless key parameter for design purposes that

characterizes transport phenomena of bubble column systems (Prakash, 2000).

It's basically defined as the volume fraction of the gas phase occupied by the

gas bubbles likewise it is possible to characterize the liquid and solid phase hold

ups as the volume fraction of liquid and solid phase, respectively. All studies

examine gas hold up because it plays an important role in design and analysis of

bubble columns (Fan& Chern, 1985&Hikita et al, 1980). It is reported that the

basic factors affecting gas hold up are: superficial gas velocity, liquid

properties, column dimensions, operating conditions (temperature and

pressure), and gas distributor design, (Reilley et al, 1986).

Peter&Cesar, 1999, suggested that column flotation is an emerging

technology in the deinking of recycled paper, dinking efficiency depends

primarily on the effect of physical properties, gas flow rate, bubble size

distribution and pulp consistency. Experiments to establish operating ranges for

Literature survey

Chapter two: Literature survey 11

these variables by determining their effects on gas hold up were conducted in a

laboratory column. The results showed that gas hold up increases with the

increasing gas flow rate and with smaller bubble size. Ru"a, 2006, studied the

influence of superficial gas velocity on gas hold up in bubble column (Air-

water system). The results found that, increasing superficial gas velocity in the

range of (0.0314-0.0754)m/sec increases gas hold up. Ben mansour et al, 2007,

studied the hydrodynamic properties in electro-flotation process, and showed

the effect of the current density, viscosity, surface tension of liquid phase on gas

hold up. He found that increasing the current density increases the gas hold up,

but it depend on liquid viscosity, where the increase in the viscosity leads to an

increase in bubble size due to coalescence phenomena as bubble size increases,

the rise velocity tends to increase, the latter phenomena lead to a decrease in

the gas hold up. Franco, 2007, Studied the sectionalized flotation column and

investigate the effect of tray hole diameter and superficial gas velocity and

liquid properties on gas hold up and on removal efficiency of contaminants. The

concluded that the smaller hole of tray is the best and caused to increase the gas

hold up and removal efficiency and increasing in superficial gas velocity

increase in gas hold up and removal efficiency. Shanmugam et al, 2008,

studied the effect of various parameters like superficial gas velocity and speed

of stirrer (N) on fractional gas hold up in bubble column of 0.14m ID and 2m

height. They concluded that fractional gas hold up increased with increaseing

superficial gas velocity and speed of the stirrer. Behnoosh et al, 2009, studied

the effect of bubble size and gas velocity on gas hold up by a cylindrical slurry

bubble column made of glass with inside diameter 0.15m and a height of 2.8 m.

They found that the total gas hold up increases at the optimum value of (0.25) at

the superficial gas velocity of about (10cm/sec) and the large bubbles have high

rise velocity and decrease the gas hold up. Sulaymon& Mohammed, 2010,

studied the effect of gas hold up on kerosene removal efficiency in QVF

flotation column with 0.156cm diameter and 1.2cm height. They found that gas


hold up increases with increasing gas velocity in the range (1.1-2.6) cm/sec, and

that caused an increase in the removal efficiency.

2.2.2. Effect of the flow rate

Puget&Massrani, 2000: studied the performance analysis of a separation

set-up characterized by the ejector-hydro cyclone association, applied in the

treatment of a synthetic dairy wastewater and the effect of (air flow rate/ feed

flow rate) were studied and the results obtained were compared with the results

from the flotation column. It was shown that better results are obtained for the

ratio (Qair/QL)>0.15 and showed lower efficiency than that obtained by flotation

column. Ying huang et al, 2003: studied the effect of flow rate on unburned

carbon removal efficiency by flotation column, a glass column measuring

500mm high and 50mm in diameter was used at the range of gas flow rate (0-

1.4) l/min. It was found that the recovery efficiency increases with increasing

the gas flow rate up to the optimum value (0.7) l/min. Above this value; the

recovery efficiency decreased because, increasing flow rate increases the

thickness of the froth zone. The results found that flotation with too high froth

zone is not effective in recovery of unburned carbon. Couto&Massrani, 2005:

studied the effect of ratio Qa/Qis (feed flow rate/saturated liquid rate) on

removal efficiency in dissolved air flotation technique that is applied to the

continuous treatment of a synthetic oily effluent (crude oil in water). It may be

remarked that the increase in Qa/Qis ratio leads to a lower oil removal

efficiency, and the higher oil removal efficiency attained in the continuous

flotation process about 90% was obtained when the process was operated with a

Qa/Qis ratio of (0.5). Puget, 2005: studied the effect of the flow rate on oil

removal efficiency in a 450ml flotation column batch mode. The range of the

flow rate was (3-6 l/min). The results showed that in 5 minutes of batch

operation, using foaming agent and using an air flow rate of 3.9 l/min, it was

possible to remove about 99.5% of oil present in the column feeding (2500

ppm) and reduce the oil concentration of the effluent to the standard allowed by

the legislation(<20ppm). Welz et al, 2007, investigated the flotation of oil


removal from wastewater in laboratory-scale, mechanically agitated flotation

cell and investigated the effect of the flow rate under optimal chemical

conditions. They found that at lowest air flow rate (2l/min) the rate of oil

removal is controlled by the stability of the froth, and found that increasing the

aeration rate increases the rate of oil removal. Turtureau &Oprean, 2008,

studied the effect of air flow rate on nickel removal efficiency by dispersed air

flotation by using a column 60cm in height. They found that the increase of air

flow rate increases the removal efficiency. Al-Maliky, 2010, used two values of

flow rates 3 l/min and 5 l/min in rectangular glass mode tank which was used as

the flotation basin that has a movable part to control the width of flotation tank.

They found that at 3 l/min and at about (1.75-2) width/height the increase in

removal efficiency is more than that at the rate of 5 l/min at the same

width/height ratio. Yinchen et al, 2010, studied the effect of the gas flow rate

(10, 20, and 40) ml/min on removal efficiency in separation of butyl acetate

from oil/water type emulsion solution by solvent sublation. They found that the

removal efficiency increased about 70% with the increase in the gas flow rate to

about 40ml/min.

2.3. Operating Conditions Affecting Removal Efficiency

2.3.1. Effect of temperature

Most plants use heat in treating process, since it provides an aid to mixing

coalescing and settling. Heat aids the treatment by enhancing the followings

(Baker, 2005):

-Reducing viscosity of the oil.

-Weakling or rupturing the film between the oil and water drop by expanding

the water.

-Altering the difference in density of the fluids and these by tending to decrease

the settling time.


-Growing droplets in size when they combine until they become heavy enough

to separate by settling down to the bottom of the treated coalescence. Heat

effect accelerates the treating process.

Connor&Mill, 1990, the effect of temperature on the flotation of pyrite has

been investigated. They concluded that increase in temperature, increases the

rate of flotation due to the decrease of the viscosity of the water thus increasing

the rate of elutriation of gangue back to the pulp. Alexander& Manrice, 2000,

studied the effect of temperature on oil removal efficiency in water –crude oil

demulsified process that carried out through "bottle test" technique. They

showed that the increase in temperature in range of (10-50) Co caused to

increase the phase separation rate by viscosity decrease. Ghazi et al, 2008,

studied the effect of temperature on Pb+2

and Cu+2

removal efficiency by

flotation. They found that the floatability of the system was not markedly

affected by rising the temperature in the range (10-80)Co, it just made an

acceleration of the flotation process. Turtureanu&Oprean, 2008, studied the

effect of temperature on nickel removal by flotation column 60cm height

dispersed air flotation. The results showed that the increasing temperature

between (20-60) Co decreased the removal efficiency to 78%. Mastouri et al,

2009, studied the effect of temperature on oil removal efficiency by induced gas

flotation. They found that increasing temperature enhances the oil removal

efficiency (85%) until reaching the optimum value of (70)Co and after this

value increasing in temperature decreases the removal efficiency about(72%).

Al-Maliky, 2010, studied the effect of temperature on the separation efficiency

of induced air flotation process of oily wastewater in a rectangular glass tank,

by using the temperature range of (0-120) Co. He found that the increase in

temperature, increases the removal efficiency until reaching the optimum value

of (80-84) Co and after that, temperature increase has an adverse performance.

2.3.2. Effect of pH


One of the most important factors to study and to show it's effect on

removal efficiency of oily wastewater. The value of pH is varied depending on

some factors like the addition of surfactant and coagulant. Most natural

particles in water and emulsifier are surfactants which have either anionic or

non ionic polar group (Reynolds &Richards, 1996). Sulfonated of fatty acids

and protein is common anionic emulsifier. Protein contains amino group (-NH2)

and carboxylic group (COOH) that their dissociation depend on the pH of the

solution. The destabilization or demulsification can be achieved with reducing

electric factor or destroys electrical double layer. By pH adjustment, pH control

can enhance the efficiency of coagulation by inorganic salt (Aneak& wirach,

2009), such as at low pH, Fe ion is surrounded with water molecule [Fe

(H2O)+3

] then was difficult to contact with collide, but at the optimum pH or

high dosage, the Fe ion can form complex to be Fe(OH)3 that is in the solid

form (Recep,2005).

Ying hung et al, 2002: studied the effect of pH on unburned carbon

removal efficiency in flotation column. They found that the removal efficiency

increases with increasing pH value in the range below the optimum pH value

where the optimum value of the contact angle decreases and the flotation

efficiency also decreases. Thamer&Eman, 2007, studied the effect of coagulant

(alum, CaO, clay) on pH value and as a result on removal efficiency in

dissolver air flotation of oily wastewater treatment. It was found that the

increase in coagulant (alum &clay) decreases the pH value (6.7) and increases

the removal efficiency, but increasing CaO, increases pH value (8.5) and

decreased the removal efficiency. Ahmed, 2004, studied the separation of

emulsified kerosene in water (concentration 250-750 ppm) in a bubble column

15.6cm diameter and 120cm height and the effect of pH was studied in range

(2.5-9)on removal efficiency. It was found that the fastest removal efficiency

was obtained when pH about 4. Ziyadanagullaril, 2005, studied the effect of

pH on flotation efficiency in the flotation of oxidized copper ore, at the range of

pH (6-11). It was found that the flotation efficiency increases with the increase


in pH until reaching the optimum value of pH (8.7) where the efficiency of

copper is 100%. Welz et al, 2007, investigated the flotation of oil from

wastewater in a laboratory scale mechanically agitated flotation cell and

explores the effect of pH on flotation performance. They found that an increase

in pH decrease the removal efficiency. Bao-yu gao&Qin-yan yue, 2007,

studied the effect of pH on oil removal efficiency in a laboratory experiments.

They showed that the removal efficiency decreases with the increase in pH at

the optimum pH range of (6-8). Turtureanu et al, 2008, studied the effect of pH

on removal efficiency in nickel removal from aqueous solution by flotation in a

laboratory scale, range of pH (8-12). The results showed that the increase in pH

increase removal efficiency, but a good separation >=98% is obtained at pH

values>=10. Ghazy et al, 2008, studied the effect of pH on copper and lead

removal efficiency by flotation by using (H2SO4, HCl, and HNO3) as

adjustment. It was found that the maximum flotation efficiencies of Cu+2

Pb+2

ions were attained on the presence of HNO3 and found that the removal

increases until the optimum value of (5-6) and after that decreases with

increasing pH. Aneak& Wirach, 2009, studied the effect of pH by acid

adjustment (HCl & H2SO4) and using coagulant (FeCl3) aid in combination with

pH control on greases and oil removal in wastewater from biodiesel process.

They concluded that pH should be low to enhance oil removal efficiency, and

the use of coagulant (FeCl3) in combination with pH adjustment may be more

practical and the oil removal efficiency 97% at the pH (4-7) and the efficiency

could be enhance by using cationic polymer as coagulant aid. Yinchen et al,

2010: studied the effect of pH on removal efficiency in separation of butyl

acetate from oil/water type emulsion solution by solvent sublation, by

cylindrical glass column 200cm in length with inner diameter of 5cm was used

for sublation. They concluded that increasing pH, decreases the removal

efficiency and the removal efficiency is in its largest value when the solution is

nearly in natural.


2.4. Geometrical Dimensions

2.4.1. Effect of Bubble Diameter and (H/D) Ratio on Removal Efficiency

Strickland, 1980, studied the flotation of oily wastewater with bubbles

varying from about (0.4-1) mm and studied the effect of various variable and

chemical compositions of the phases on over all system performance. His

results agree with Reay's theoretical predications of the effect of drop size

bubble size and gas concentration on overall removal efficiency. Fatemeh et al,

2006, studied the effect of salinity and pressure on bubble size and the removal

efficiency in the removal of organic pollutants from waste streams where the

micro bubbles produced by saturation of air in a pressurized packed column

where released in an atmospheric column leading the bubble to rise. It was

found that increasing pressure and salt concentration decrease the size of bubble

and increasing removal efficiency. Ru'a, 2006, studied the effect of column

diameter on gas hold up in bubble column. The results showed that the gas hold

up decreases slightly with increasing column diameter because the bubble

accelerated, this acceleration effect causes a significant reduction in gas hold up

with increasing diameter. Ben mansour et al, 2007, studied the hydrodynamic

in electro flotation process and studied the effect of liquid viscosity, surface

tension and current density on the average bubble diameter. They found that the

average bubble diameter increases with increasing the current density, but

decreases with decreasing both liquid viscosity and surface tension, the

influence of current density on the average bubble diameter is also significant

only at specific internal of variation.

Shanmugam et al, 2008, studied the effect of height to diameter (H/D)

ratio on the fractional gas hold up in bubble column of 0.14m ID and 2m

height. They found that increasing (H/D) ratio decrease the gas hold up

gradually. Behnoosh et al, 2009, studied the effect of bubble size on gas hold

up in a cylindrical slurry bubble column made of a glass with inside diameter of

0.15m and height of 2.8m. It was found that the initial bubble size is depended


on the sparger type; the large bubbles have higher rise velocity and decrease the

gas hold up and removal efficiency. Al-Maliky, 2010, studied the effect of

geometrical dimension (width: height) on the separation efficiency of induced

air flotation process that handle effluent of dairy industry, six ratios were tested

(1:1), (1.25:1), (1.5:1), (2:1), (2.25:1), (2.5:1) in rectangular glass mode tank,

used as the flotation basin, that have a movable parts to control the width of

flotation tank. He found that the best dimensional configuration for an inducer

air flotation approach (of rectangular flotation tank) for oil/water separation was

proven to be via the adoption of flotation tank (1.75:1, 2:1) width/height ratio.

2.4.2. Effect of Sparger Type

Gas sparger type is the parameter that can alter bubble characteristics

which in turn affects gas hold up values and thus many other parameter

characterizing bubble column (Oyeraar et al, 1991). There are numerous type

of gas sparger, which significantly differ in their size and number of orifices,

porous plates, perforated plates (sieve plate/sieve tray), multiple /single –

orifice nozzle, bubble cups, perforated rings, annular shears, spider-type in

injectors, and hollow fibers among others account for the most commonly

distributors employed in the bubble column reactors (Behkish,2004). Figure

(2.1) illustrates some of these gas distributors. The characteristics of gas

spargers include among others opening size, number of openings, distributor

positioning, and nozzles position/orientation (Mustafa, 2004). The initial

bubble size and distribution at the orifice could be controlled by the distributor

characteristics (Oyeraa et al, 1991, Jung& woo, 2004). (Camarasa, 1999)

used aqueous non-coalescing solutions and water to compare the effect of

porous plate, multi-orifice nozzle and single-orifice nozzle on the gas hold up as

shown in Fig. (2.2).


Figure (2.2):Average gas holdup data in the air-water system (Camarasa, 1999)

They found that bubble characteristics in water with porous plate and multi-

orifice nozzle were comparable, where as the trend was different in non-

coalescing solution on the other hand the single- orifice nozzle is completely

different compared with the two other distributor.

Mustafa 2004,studied the effect of distributor type on gas hold up, by

using two types of distributor (porous, perforated) in a QVF glass bubble

column with 0.1m inside diameter and 2m height. The results showed that the

porous plate gives higher gas hold up than the remaining perforated plate. Jung

and Woo, 2004, showed that the bubble properties in the column flotation

system are deeply affected by the bubble-generator type, frother dosage, and

superficial gas velocity. This study is to determine the bubble-generator type,

which effectively produces micro-bubbles to affect the flotation efficiency.

Characteristics for two types of bubble generators like the in-line mixer and

sparger are examined by bubble properties such as bubble diameter, holdup and


bubble velocity. Micro bubbles generated from an in-line mixer result in the

increase of the bubble rising velocity and gas holdup. Bubbles produced at the

in-line mixer were more effective for operating the flotation system than that of

the sparger. It means that the in-line mixer bubble generator is more effective

than a sparger in designing or operating the column flotation system. Puget

2005, studied the treatment of oily waste coming from air compressor by using

flotation column, the column is constituted by a consolidated porous medium

composed of sand and araldite with the aim to develop a new form of use for

the porous medium to decrease the operating costs of the process and turned the

experimental unit very versatile, compact and efficient. The porous medium is

used as a disperser of air bubbles and in the end the batch it used as a filter

medium. Benhoosh et al, 2009, studied the effect of sparger type in different

gas velocity in cylindrical slurry bubble column made of glass with inside

diameter of 0.15m and a height of 2.8m, two types of sparger were used,

namely a porous plate and a perforated plate with the same porosity. They

found that the porous plate with smaller pore diameters generate smaller gas

bubbles compared with perforated plate therefore the gas hold up in system

equipped with porous plate at high superficial gas velocity is approximately

40% higher than system equipped with perforated plate.

2.5. The Effect of Surfactant and Additives on Removal Efficiency

Surfactants are surface active contaminants whose molecules have

hydrophobic and hydrophilic parts. The hydrophobic part tends to align itself in

the air, while the hydrophilic part aligns itself in the water, thus surfactants tend

to be found at interfaces (Bel Fdhila et al, 1996). Electrolyte solutions,

aqueous alcohol solutions, polymeric dilute solutions and fatty acids are

surfactants (Kulkarni et al, 2005). The important effects of surfactants are that

these substances reduce surface tension and inhibit the formation of large

bubbles, furthermore, causing the bubbles rising with lower velocity (Rodrigue

et al, 1996). The modern theory of the mechanism of surface action is


intimately related to the fundamental work of (Harkins et al. & Langmuir)

with the phenomenon of molecular orientation at interfaces.

All surfaces capable of surface action are composed of relatively large

molecules which contain widely separated groups of dissimilar nature. It is

characteristic of these substances to be surface –active in quite dilute solution,

this ability to function effectively in low concentration is due to the tendency of

the molecules to concentrate at interface between the solvent and a gas, solid, or

other immiscible liquid, at the boundaries of the solvent there is an orientation

of molecules according to the nature of the substances forming the interface. If

the solvent is oily, the hydrophobic hydrocarbon chain or "tail" of the molecule

is orientated toward the solvent (oil) and the hydrophilic or polar "head" is

directed toward other phase (water), where orientation of the surface active

molecules at the surface of the droplet forms a protective film which prevents

the droplets from coalescing on contact with each other, Daniel swern, 1979.

Angelldon et al, 1977: studied flotation of oil drops using air bubbles of

0.15mm diameter and found that NaCl salts decrease the flotation rate. Wasan

et al, 1979: has shown that surfactants which act to lower the interfacial

viscosity also act to destabilize crude –oil emulsion. Ying huang et al, 2002:

studied the effect of collector dosage (kerosene) on unburned carbon removal

efficiency in flotation column. They found that the use of kerosene increase

unburned carbon recovery efficiency compared with flotation with out collector

kerosene and when excess collector was added decrease the flotation efficiency.

Thamer&Eman, 2007, studied the effect of coagulant (alum, clay) on removal

efficiency of oily wastewater treatment by dissolved air flotation. They found

that the removal efficiency of oil increase with alum until reaching the optimum

dosage (25, 40, 70) ppm for initial oil concentration (30, 58, 136) ppm

respectively, and the over dosage causes a decrease in the oil removal

efficiency, but the other coagulant (clay) having higher removal efficiency of

oil the optimum dose of it was (2.5, 5, 9) ppm for the same initial oil

concentration, but disadvantage of higher amount of sludge caused. Soletti et al,


2005, studied the effect of ferric sulfate Fe (SO4)3 on pH values in dissolved air

flotation of oily wastewater treatment by flotation column and obtained increase

in coagulant concentration decrease pH value and enhance removal efficiency.

Lima& Patrico ,2005, studied the use of an anionic surfactant in the recovery

process of organic compounds present in oily effluents from petroleum industry

separation process using gaseous bubbles formed by the passage of a gaseous

stream through a liquid column, surfactant concentration from(0.045-4.545)g/l

at a fix flow rate (500)cm3/min. They found that the efficiency was around 80%

when concentration of surfactant is (0.09)g/l. Puget, 2005, showed an

aluminum sulfate solution was used as flocculating agent (optimal

concentration determined by jar test) also laurel ether sodium sulfate was used

as foaming agent to improve the efficiency of oil removal by flotation column.

It was found that the best result (efficiency 98%) was obtained with 155ppm of

aluminum sulfate and SLES on 3.33mg/l, this concentration was used to reduce

the waste superficial tension and to improve the oil removal efficiency.

Welz et al, 2007, investigated the flotation of oil from wastewater in a

laboratory -scale mechanically agitated flotation cell and explores the effect of

chemical factors (coagulant & flocculants) on flotation performance based on

coagulant and flocculants dosages of (0.5 mg/l) when using Al2(SO4)3 and

1.5mg/l when using lime. They found that the effect of coagulant dosage is

more economical with the use of Al2 (SO4)3 is the further justified due to lower

cost as well as lower dosage and higher efficiency. Shanmugam et al, 2008,

studied the effect of adding electrolytes like NaOH ,BaCl2 ,MgCl2 ,NaCl of

various concentration on gas hold up in bubble column of 2m height and 0.14m

I.D. They found that the fractional gas hold up increased for electrolyte solution

when compared with pure water, and the addition of electrolyte increased gas

hold up initially, but further addition of electrolyte of excess concentration

doesn't affect the gas hold up considerably. The gas hold up increased with

addition of electrolyte in the following trend MgCl2<NaOH<BaCl2<NaCl.


Adel&Luma, 2009, studied the addition of demulsifiers (RP6000, Chimec2439

and PAA) for dehydration (desalting) of Al-Basra water in oil emulsion. The

parameters where demulsifier dose (10-80) ppm, separation time (5-120) min.

They found that the dehydration efficiency with prepared demulsifier (PAA)

was 75%, the two of commercial demulsifiers also used (RP6000 and

Chimec2439), which gave water separation efficiency (87.5% and 72.2%),

respectively. Sulaymon& Mohammed, 2010, studied the effect of coagulant

Al2 (SO4)3.17H2O and surfactant on separation efficiency of the emulsified

kerosene in water in bubble column. The results indicate that the rate of the

flotation enhanced when using SLES (sodium laurel ether sulfate) where the

surface tension was reduced which leads the improvement of the separation

efficiency, and found that adding Al2 (SO4)3.17H2O and SLES together have a

high coagulant effect than individually.

2.6. Hybrid Treatment (Coagulation –Flocculation-Flotation)

Flocculation and flotation processes in the mineral industry are primarily

designed to separate one particle type from another. In contrast, for wastewater

treatment, the flotation is designed to remove all particles— generally

encountered as very fine emulsions, suspended solids, microorganisms and

colloidal dispersions. Thus, processes are optimized by the maximum recovery

of cleaned water with the lowest concentration of pollutants and sludge

containing low percentage of solids (or oils) (Rubio, 2003).

A new turbulent on-line flocculation system assisted with air bubbles has

been developed at LTM (Laboratory Technological Mineral) yielding aerated

flocs (flocs with entrained and entrapped bubbles). These flocs, which rapidly

‘‘float’’, are formed only in the presence of high molecular weight polymers

and bubbles and under high shearing in the flocculator (Fig. 2.3). The excess air

leaves the flotation tank (a centrifuge) at the top and the flocs float after very

short residence times (within seconds). The aerated flocs are large units (some

millimeters in diameter) having an extremely low density (Rubio, 2001).


Figure(2.3):The FF pilot system used in the removal of oils from oil-in-water

emulsions (Rubio, 2001).

Zouboulis,&Arranas, 2000, showed the treatment of oil-in-water

emulsions containing n-octane (used as simulated wastewater) was investigated

by means of dissolved-air flotation jar-tests. The effect of several parameters on

flotation efficiency for separation of the emulsified oil was examined, namely,

(a) the presence the nonionic surfactant Tween 80, used for the stabilization of

the emulsions, (b) the initial pH value of the emulsions, (c) the concentration of

chemical additives, such as polyelectrolyte (organic flocculants of cationic or

anionic type) or ferric chloride (inorganic coagulant), (d) the concentration of

sodium oleate (used as flotation collector) and (e) the recycle ratio. The use of

polyelectrolyte was not able to effectively treat the studied emulsions, while the

addition of ferric chloride and the subsequent application of dissolved-air

flotation were found very efficient. At the optimum defined experimental

conditions (recycle ratio: 30%, pH: 6, [Fe3+

]: 100 mg l−1

and [sodium oleate]:

50 mg l−1

) more than 95% of the emulsified oil was effectively separated from

an initial concentration of 500 mg l−1

. Jailton& Jorge, 2004, A new on-line

flocculation system (FF) has been developed which is coupled with a rapid

flotation to remove the aerated flocs (flocs with entrained and entrapped

bubbles). These aerated flocs are formed only in the presence of high molecular


weight polymers and bubbles and under high shearing (and head loss) in special

‘‘flocculators’’. The result showed successful examples of emulsified oil and

solids removal from water and that because in all cases were obtained high

efficiencies (>90% removal), at high hydraulic loadings (>130 m/h) it is

believed that this kind of flocculation–flotation appears to have a great potential

in solid/liquid or liquid/liquid separation. Weichun Yang et al, 2008, Aiming at

handling oily waste water of steel-making enterprise, active separation of oil-

coagulation-floatation-slag filtration technology routing was designed. Via

static test, poly aluminum chloride etc. Three kinds of coagulant were primarily

selected. Coagulant for treating effect and rational operating conditions were

determined. Optimized operating condition was: poly aluminum chloride

dropping quantity was 50~70 mg/L, air solubility was about 45 mg/L, gas-oil

ratio was 0.53 ml/mg or so, appropriate size floatation tank, slag filter column.

Under the medicine dropping quantity and air solubility, wastewater oil removal

rate reached more than 90%. Shu liu et al, 2009, In order to enhance the

pretreatment effect of dyeing wastewater, comparison experiments of

coagulation micro-bubble floatation and coagulation conventional air bubble

flotation were carried out. The results demonstrated that coagulation micro-

bubble flotation significantly reduced coagulant doses and enhanced the

pretreatment rate, because the usage of micro-bubble generator produces fog-

like micro-bubbles with diameters in tens of micrometer, which has longer

preservation time in the water. In addition, the micro-bubbles could reach a

higher oxygen transfer rate: the total mass-transfer coefficient of micro-bubbles

was 1.1754 min−1

, and that of conventional air bubbles was of 0.7535 min−1

.

Under the same conditions, the removal efficiencies of COD, color and oil for

the micro-bubble floatation increased 30%, 110% and 40% respectively,

compared with the conventional air bubble flotation. Furthermore, the

wastewater biodegradability was increased from 0.290 to 0.363 after

coagulation micro-bubble flotation and to 0.301 after coagulation conventional

air bubble flotation. The application of the micro-bubble technology in


coagulation processes may provide an efficient and cost-effective approach.

Paimanakul et al, 2010, studied the treatment of oily wastewater containing

anionic surfactant at micelle concentration (CMC) by IAF and MIAF process in

flotation column with 0.05 m in diameter and 2m in height. The MIAF process

combined between the IAF process and the coagulation process and found

interfacial area(a) and (G) values experimentally in MIAF and IAF and their

effect on the removal efficiency. It was shown that the removal efficiencies

obtained with the optimal gas flow rate(5ml/s) in MIAF process are greater

than obtained by IAF process of about(97%) , and found when (a) increase

(R%) was increased, and the velocity gradient (G) have been proven to be the

important parameter for controlling the flotation process efficiency and

operating cost.

2.7. Empirical Correlations

2.7.1. Bubble rise velocity

Zuber and Hench (1962), provided a prediction for the rise velocity of

bubble swarm under condition were the bubble swarm rises in a stagnant liquid

in laminar motion these authors proposed:

……... for db < 0.05 cm ……..……..….....….. (2.1)

… for 0.05 < db < 2 cm ……………………(2.2)

At higher Re number bubbles lose their separate identity and a region which

Zuber et al. (1967), described as the churn turbulent bubbly regime is

encountered. They recommended the following correlation:

4/1

241.1

l

br

gU

………………………………………………………...... (2.3)

G

L

G L br

g U

1 41 . 1

3

2

1 18

G L

b G L br

r

d U

g


The magnitude of the wall effects depends on the ratio of the bubble

diameter to the column diameter, db/DC. When the column diameter is large

enough, the bubbles are free from wall effects. The Davies-Taylor relationship

is found applicable, provided the ratio db/DC < 0.125. For values of db/DC

exceeding 0.125, Collins, 1967, introduced a scale correction factor, SF, into

the Davies-Taylor relationship:

dgdgU

b

bbr 71.0

2 ……………… ………………… ....….… (2.4)

)(71.0 SFdgUbbr ............................................................... (2.5)

This scale correction factor was determined empirically to be given by

Collins, 1967, as follows:

SF=1 … for 125.0D

d

C

b …………………….…….… (2.6)

for 6.0125.0 D

d

C

b ………………….....……(2.7)

d

DSF

b

C496.0 for 6.0D

d

C

b ………………………………....(2.8)

Bhatia (1969), attempted to extend Mendelson's wave analogy further to

describe the rise velocity of a swarm of bubbles they obtained the following

correlation:

…………………………………………..… (2.9)

In the column flotation, drift flux theory states that the hindered bubble rise

velocity (Ubr) is defined by:

……………………………………………….. … (2.10)

Where Jg is the superficial gas velocity, Jl is the superficial liquid velocity, and

g is the fractional air holdup.

g

l

g

g br

J J U

1

D

d

C

bexp13.1SF

3/1/125.0tanh Gtgs UU


Koide (1979) employed the electroesistivity probe to measure bubble rise

velocity locally and calculated the average bubble rise velocity. The bubble rise

velocity in the central area of the column was approximately (60-150) cm/sec.

The following equation was used:

b

br

brN

UU

……………………………………………….....…… (2.11)

Finch &Dobby 1990, provide a prediction for the rise velocity of bubbles in

flotation column for bubble size db<= 2mm (Re<=500)

(2.12) Ubr=Jg/g

Where Jg is the superficial gas velocity and g is the fractional air holdup.

The knowledge of terminal rise velocity of a single bubble is used in

conjunction with the interaction of neighboring bubbles to provide a better

assessment of the mean bubble rise velocity in the swarm as follow (Ruzicka et

al., 2003):

G

FUtgsU ………………... …………………………..……….…..… (2.13)

Where )( GF , represents the effect of the interaction of the neighboring

gas bubbles.

2.7.2. Bubble Size

For very large gas flow rate, Lehrer (1971), proposed the following

equation:


2.0

BD

4.0

Gb

g4

)C(3

N

Q05.2d

………………………….………...... (2.14)

The drag coefficient of bubbles (CD)B ranges as follows:

B

BDRe

24)C( for laminar chain bubbling ……………………...…. (2.15)

…………..………….. (2.16) for turbulent chain bubbling3

8)( BDC

Akita and Yoshida (1974), showed that the gas bubble diameter is only

slightly depends on the gas velocity in case the gas is sparged by single orifice,

or perforated or sintered plates. They determine the bubble size distribution in

bubble column using photographic technique, the gas sparged through

perforated plates and single orifices and various liquids (water, aqueous and

pure glycol, methanol, and carbon tetrachloride) were used and they proposed

the following correlation:

12.012.0

2

35.0

2

26

c

g

Lc

clc

c

b

gD

u

u

gDgD

D

d

…………………..…(2.17)

This correlation is based on data in columns up to 0.3 m in diameter and up

to superficial gas velocities of about 0.07 m/s. Though equation 2.17 indicates

that db is proportional to 3.0

cD , for Dc>0.3 m bubble diameter becomes

independent of column diameter.

Guy et al. (1986), proposed the expression of bubble diameter in

cylindrical bubble column (height of 0.9 m and diameter of 0.254 m) as a

function of Bond, Galileo, and Froude numbers as well as the ratio of orifice

diameter to the column diameter.

………………………………………… (2.18) ……..

D

dFrGaBof

D

db ,,,


Benhoosh, 2009, measured the bubble size distribution in gas-liquid bubble

column by digital camera and analyzed the result by computer programming

and Abdullah et al, 2002, studied the effect of hydrodynamic interaction in

bubbly two-phase component flow in bubble column. They measured bubble

parameter by neutron transmission technique in addition to a high speed

camera.

2.7.3. Gas Hold up

Table 2.1 shows some of the empirical correlations. The comparison

between measured and predicted gas hold up values are illustrated below in Fig.

(2.4). It can be seen that Haikita's & kikukaw correlation is the better than other

correlations for estimating gas hold up.

Table (2.1): Empirical correlations for gas hold up ((Behnoosh et al, 2009)

Author Correlation

Kumar et al,

1976

412

30975.0

2485.0728.0

glgVU

UUUg


Hikita et al ,

1980

strengthionicoffunctionaisfsolutionsionicfor

solutionseelectrolytnonandliquidspureforf

l

g

l

g

l

gllgV

fg

,1

107.0062.0

131..0

3

4578.0

672.0

Hikita&

kikukaw,1974

05.03

2

47.0 001.0072.0505.0

l

gg V

Reily et al

,1987 19.016.098.044.0296009.0 glsllgg orV

Hugmark et al

,1967

1

,1

,1

3135.02

1

cmdyningcminl

msingV

lgVg

ww

Figure (2.4): Comparison between correlations and

experimental data (Behnoosh et al, 2009)

The bed expansion technique is the most common procedure for measuring

the overall average value of gas holdup of the bubble column, where no foam is

present. The gas holdup ( g ) is measured by visually recording the dispersion

height Hf above the gas distributor, Ruzicka et al. (2001).


The following relation determines the average gas holdup as a function of

the superficial gas velocity Ug

g

HHH

f

f

…………………………………………..………….. (2.19)

Where Ho is the initial height of the liquid in the column, and Hf is the

expanded height of the liquid after aeration of the column with constant

superficial gas velocity at steady state.

The manometric method is used for the measuring of the pressure drop

across the bubble column. A glass manometers filled with mercury is connected

to the bubble column. The value of gas holdup g for each gas velocity is

estimated using experimental value of pressure drop obtained, Saxena (1989).

The equation mainly used is:

g Zg

p

gl

)(1

………………………………………………. (2.20)

2.7.4. Removal Efficiency

Couto&Massrani, 2005: The flotation efficiency of the treatment of oily

effluent (crude oil) was calculated according to the equation below:

R%= (1- C/Ca)*100 …………………………………………….…… (2.21)

Ca ,C are the oil concentrations in the feed and clarified effluent streams

respectively

Puget &Massarani2000: evaluated the efficiency of separation milk powder

in water by means of the following equation:


R%=1- [(COD)U/(COD)L]*100 ……………………………………….(2.22)

Where (COD)U&(COD)L are the Chemical Oxygen Demand in the under flow

&feed flow respectively. Painmanakul et al, 2010, analyzed the amount of oily

wastewater in term of Chemical Oxygen Demand (COD) according to the

procedures described in standard methods as a function of operation time

obtained in flotation column (standard methods for the examination of water

and wastewater, 1998). Therefore the removal efficiency at different operation

times can be calculated by:

R%= (COD)o-(COD)t/(COD)o ………………………………………….(2.23)

Puget 2005, considered the turbidity to be a good parameter for controlling

the efficiency of flotation process and it was determined using a

spectrophotometer operating at 460nm. Distillated water whose transmittance is

100% was used during the analysis. The oil removal efficiency was calculated

using equation 2.24:

R %=(TTW-TWF / TW-TWF)*100 ………………………………………….(2.24)

Where: TTW is treated waste transmittance (%)

TWF is waste feed transmittance (%)

TW is water transmittance (%)

2.8 Summary

It can be concluded from the literature review that the important

hydrodynamic characteristics in flotation column was (gas hold up, bubble size,

gas flow rate, type of the distributor). Also other parameters, such as pH, type

of surfactant, coagulants type, concentration oil of wastewater, can affect oil

removal efficiency. Although there are multi equations to correlate the


hydrodynamic parameters, but still the research work required more

experiments to consider the interaction of these parameters with adding new

surfactant and new technique to get clear water <10 ppm oil concentration or

higher removal efficiency. From above literature, the nearest papers to the

present work are Painmanakul et al, 2010, and Sulaymon& Mohammed, 2010.

The literature review for flotation processes indicates shortage to express the

experimental results in a general equation on dimensionless group, therefore in

the present work, dimensional analysis equation for the removal efficiency will

be derived to express the interaction between the variable, and another

correlation for the stirrer in the flotation column to improve removal efficiency

will be suggested namely, modified flotation by the stirrer.

Chapter three

3.1. Introduction

This chapter contains the experimental runs to measure the efficiency of oil

removal from oily wastewater from the North Oil Company at different

parameters, such as different oil concentration, different flow rates, different

additive in different concentration (alum, sodium laurel sulfate, camper) and

different pH, by using flotation column fitted at the bottom with porous

distributor (120 m) to generate bubbles. Also some experiments were carried

out by using perforated plate with hole diameter (2mm) to compare with porous

distributor.

3.2. Characteristic and Preparation of Sample Wastewater

The properties of oily wastewater (crude oil in water) from the (North Oil

Company) at different concentrations are shown in Tables.3.1 and 3.2, and to

make it stable before the treatment it was mixed with blender (3000 rpm) for

10 min, and subjected to flotation experiment. The stability of emulsion was

checked by bottle –test , the bottle test is an empirical test in which varying

amounts of potential demulsifiers are added into a series of tubes or bottles

containing sub sample of an emulsion to be broken. After some specific time,

the extent of phase separation and appearance of the interface separating the

phases are noted (Auflem, 2002).

Experimental Work

Chapter three: Experimental Work 36

Table (3.1): properties of wastewater*

Pollutants Before lagoon After lagoon PH 6 7.2

Conductivity (µs/cm) 1057 1017

Total Dissolved Solid (TDS) mg/l 739.9 711.9

COD mg/l as O2 Hi 66.4

OIL mg/l 19786 30

H2S mg/l 3.4 Nil

Turbidity (NTU) 304.7 4.04

Total Hardness (T.H) mg/l 600 475

Calcium mg/l as CaCO3 525 425

Magnesium mg/l as CaCO3 75 50

Chloride mg/l as Cl-

130.46 86.97

Sulphate mg/l as SO4-2

504 312

Total iron mg/l as Fe Nil Nil

Copper mg/l as Cu+2

Nil Nil

Manganese mg/l as Mn+2

Nil Nil

Nitrate mg/l as NO3-

Nil Nil

Table (3.2): Physical properties of the crude oil

Density(Kg/m^3) 829 Viscosity(Kg/m.sec) 0.0023 API 35.3 Surface tension(N/m) 0.0285

* All these examinations were carried out by Petroleum Research and

Development Center (Ministry of Oil).

3.3. Materials

Surfactant sodium laurel sulfate (SLS) was used as anionic emulsifier, it's

molecular weight is equal to 288.38 gm/mole and it's purity is 90%.

Aluminum sulfate (Alum) Commercial alum was used in the experiments, it

is a white dry powder, has a formula of (Al2 (SO4)3.18H2O) and molecular

weight of (594.4 gm/mole).

Surfactant camper (Cocamidopropylamine Oxide) it is an amphoteric

surfactant, its yellow oil with the molecular weight of 309.


pH adjustment was done by using (NaOH molecular weight is 40 gm/mole and

purity of 100%, HCl molecular weight is 98.08 gm/mole and purity of 100%).

Normal Hexane was used as a solvent and Anti-Foam.

Carbon tetra chloride.

Distilled water.

3.4. Experimental Set up

The experiment apparatus is shown schematically and photographically in

Figs. 3.1 and 3.2 respectively, details are given in the following section:

3.4.1. Flotation column

The experiments were performed into a cylindrical Perspex glass flotation

column with the dimensions (10 cm I.D and 150 cm in height) and operated in a

semi- batch mode (batch wastewater, continuous air). The drop oil sizes

distribution were found by using microscope and the mean drop diameter was

found to be equal to(44)m ,The inner column had (3) sample ports arranged

axially the first one (10 )cm above the bottom of the column, the other two taps

arranged at interval of 50 cm, these taps were glued by means of super glue,

also (2)pressure taps located along the column, arranged at interval of (35

)cm. The pressure taps were connected to manometer by plastic tube of (10)

mm inside diameter filled in water to measure the local gas hold up. The bottom

of the column connected to a conical joint of QVF glass by flanged joint the

conical joint contained two types of bubble generators. The first one was an

orifice gas distributor which was made of Perspex plate with (70) drilled holes

and of a diameter (2mm), the drilled holes were distributed on the Perspex plate

with suitable rectangular pitch, the design of gas distributor was cited in

appendix (C). The second one was a porous ceramic distributor of 0.09m

diameter, and with pore size (120 m). The pore size was determined by

Scanning Electron microscope Model (Olympus, BX51M) as shown in the

photograph (Fig.3.3). The porous ceramic plate and the Perspex gas distributor


were supported by epoxy resin inside the conical section. In order to achieve

effective mixing in the column the stirrer used was (50-250) rpm in rotational

speed and consisted of a shaft 120cm in height and 6 mm in diameter made

of stainless steel, and a paddle with a diameter of 8 cm and thickness of 1.5

mm . The rotational speed of the impeller is controlled by an autotransformer

connected to a D.C motor (Heidolph). The reading of the motor was calibrated

by using digital tachometer (cited in appendix B) and another calibration curve

in the same Appendix shows the relation between the velocity gradient and the

speed (rpm). The high speed camera type (SONY-DSC-HX1) was stationed in

front of the test column to measure the bubble velocity and size.

3.4.2. Gas Delivery

Air was used as the gas phase supplying to the column by means of

Compressor type (Assomel A 52-8-100/ Italy); the compressed air was

passed through a stabilizer, and then fed to the column via a filter

dryer(ELCO type) to remove water and any other impurities from

the gas before introduced into the system. The gas flow rate was

adjusted with the aid of a needle valve and a calibrated rotameter of capacity

(30) l/min was used in this work. The rotameter was calibrated by using a gas –

meter Model (Gallenkamp and with accuracy 0.025%), the calibration curve of

the rotameter is illustrated in appendix (A). The range of superficial gas

velocity which is used in these experiments was varied from (0.006363-0.0636)

m/sec.

3.4.3. Experimental Procedure

The procedure is concluded by the following steps:

Oily water with different concentrations (30 up to 800 ppm) was poured

gently at the top of the column on 70cm from the height of the column in

different gas velocity (0.006363-0.0636) and after (25) minute the samples were

taken from a sampling port 10 cm above the bottom of the column to determine


the oil removal efficiency for the sample analyzed for oil concentration using

UV-1100, and also during the run the hydrodynamic characteristics were

measured (gas hold up, bubble size and bubble rise velocity).

The experimental runs to investigate the effect of flotation time analysis

were carried out by taking the sample each 5 minute and analyzed by UV-1100.

To study the effect of different surfactants on efficiency of flotation column,

the experimental procedure above was repeated with treatment of oily

wastewater by adding the additives SLS, Camper, Alum separately.

The above experiment runs were repeated for the following cases studied:

Different pH (4.3, 7, and 8.5) at a constant gas velocity and surfactant.

By using a mixer (50-250rpm in range of speed) called Modified Induced

Air Flotation process (MIAF).

By taking the sample in different location from the column (10, 25, and

50cm).

Some experiments was carried out to show the effect of additive in different

dose on COD and BOD removal, the final COD and BOD was measured

according to standard methods for the examination of water and wastewater,

1998, using LEVIBOND spectrophotometer system.


Schematic diagram for the experimental apparatus: (Figure (3.1

(9)monometer 1) Air

compressor

10)&(11)Pressure taps) (2) filter

(12)&(13)&(14)sampling

valves (3) needle valve

(15)stirrer (4)Rota meter (16)motors (5)pressure gage (17) camera (6)check valve (18)PC 7)drain valve)

(19) Flotation column (8)distributor


3.2): Photographic diagram for the experimental apparatus. Figure.


(a) (b)

Figure (3.3): The pore size of the distributor where (a) 50 time zoom and (b)

100 time zoom

3.5 Determination of Oil Concentration

3.5.1. Outline of the Method

The oily wastewater is extracted from the water with carbon tetra chloride.

Then the absorbance of the extract is determined with the use of Ultraviolet

Spectrophotometer (Takahashi et al.1979), and the oily matter concentration

was taken from the calibration curve as shown in Fig. 3.4. The apparatus and

materials were:

- Ultraviolet spectrophotometer (UV) type 1100.

- Separating funnels of 250 ml capacity.

- Pipettes of various sizes.

- Sodium chloride analytical grade.

- Carbon tetra chloride spectroscopic grade.


3.5.2 Calibration

0.3 gm of the crude oil was dissolved in 500 ml of carbon tetra chloride that

called (stock solution). Different concentrations were obtained by dilution with

CCl4. Absorbance of those samples are measured by UV spectrophotometer at

285m. The Figure (3.4) shows the concentration against absorbance show

linear relationship for the range of concentration studied (10 to 600 ppm).

0

0.6

1.2

1.8

2.4

3

3.6

4.2

4.8

5.4

6

0 80 160 240 320 400 480 560

Concentration(mg./lit.)

Ab

so

rban

ce

Figure (3.4): Calibration curve

3.5.3 Procedure

Small quantity of NaCl was added to the wastewater in the separating

funnel in order to break the emulsion of oil. 5 ml of carbon tetra chloride was

added and followed by vigorous shaking for 3 min. After 30 min, when the

solution separated into two distinct layers, the lower (organic) layer was taken

for the absorbance measurement, and from the calibration curve, concentration

of oil was obtained.

3.6. Bubble Size and Rise Velocity Measurement

The bubble size and Rise velocity thought-out the operation was measured

using digital high speed camera type (SONY-DSC-HX1), 9.1 mega pixel, and


20X optical zoom, connected to PC (Laptop type Acer) in order to analyze the

images by computer programming. Figure (3-5) shows the image from the

present work. The mean bubble size and rise velocity were measured in this

camera in the following method:

A small spherical ball (0.001 m) outside diameter made of plastic was

immersed in the liquid of the test region of the column. Air bubbles were

introduced in the test region of the column which contained the ball. And the

pictures which appeared on the monitor of laptop were also recorded on the disk

of the video. The camera was stopped and the video was operated at slow rate

to show the pictures of the bubble and the plastic ball on the monitor. By using

the appropriate proportionality factors and the variables, bubble size and bubble

rise velocity were measured by camera and the average values were taken

through three zones.

Figure (3.5): present work


3.7. Sample wastewater treatment

Figure 3.6 shows a picture of the wastewater sample, where the first

cylinder is the emulsion before treatment and the second is the water after

treatment when adding alum and the third is water after treatment when

adding sodium laurel sulfate during the operation.

(1) (2) (3)

Figure (3.6): Samples of wastewater before and after treatment.


20 cm

20 cm

20 cm

10 cm

Chapter Four

4.1. Determination of Rate Constant

A number of complex chemical and physical interaction aspects are involved

in the flotation process. An extensive work is reported in the literature on the

study of this process, which has been studied from different angles. Of these,

kinetic approach has been highly instrumented in better understanding leading

to reasonably accurate prediction (Hernainz and Calero, 2001).

The qualification of kinetic parameters has an increasing importance in

industrial flotation to shed light on the speed of the process. Many researchers

have studied the kinetic aspects of froth flotation paying special attention to

particle size, bubbles and their complex interactions (Trahar and Warren,

1976).

Arbitor and Harris (1962) found that the flotation kinetics in the study of

the variation in amount of froth overflow product with flotation time and the

quantitative identification of all rate-controlling variables maintained constant.

The algebraic relationship between the proportion of mineral floated and

flotation time is a flotation rate equation. This contains the constant values of

all the rate determining variables implicit in one or more rate constants, which

must be evaluated from experimental data.

By analogy with chemical kinetics, the equation representing flotation

kinetics may be expressed (Hernainz and Calero, 2001) thus,

nkCdt

dC …………………………………………………………(4.1)

Where C is the concentration of oils, t is the flotation time, n is the order of the

process, and k is the flotation rate constant.

Theoretical concepts

Chapter four: Theoretical concept 47

Three approaches may be used to calculate this constant, namely first order

equation (n=1), second order equation (n=2), and non-integral-order equation.

Investigation of the flotation kinetics is an important task, which contributes

to determine process feasibility and to establish design equations for equipment

operation and scale-up purposes. Santos, 1996, proposed different approaches

for flotation kinetics investigation. The simplest one utilizes a reaction model to

represent flotation kinetics, as indicated below.

aX(Particles) + bY(Bubbles) k→ cZ(Floatable Aggregate)

Thus, the rate of “particle consumption” by flotation, for an order reaction, is

given by Equation below:

d[C(t).V(t)]/dt = -k.V(t).C(t)n …………………………………………………..(4.2)

C(t) is the concentration of particles inside the flotation tank, V(t) the tank

volume and k the flotation kinetic constant.

The column was regulated to operate in batch mode. It is of fundamental

importance to evaluate the variation of oil concentration as a function of time to

understand oil removal mechanism by the air bubbles. Based on the exposed,

the differential methodology was used (concentration dependence parameter

and column physical parameter) (Fogler, 2002), in which the concentration data

vary as a function of contact time. As the extraction column operates in an

isothermal way, at a constant volume, and assuming that the law of oil speed

extraction is

- r = κ* C, and from the combination of the molar balance with the extraction

speed, Equation (4.1) was obtained:

- (dc/dt) = k*C η

Where: k is the column physical parameter and η is the concentration

dependence parameter. Applying the logarithm in both sides of Equation (4.1),

Equation (4.3), is obtained


-ln (dc/dt) =ln k+ ηln C ………………………………………………… (4.3)

Using the experimental data of concentration versus time and applying a linear

fit, the concentration dependence parameter (η) and the column physical

parameter (κ) can be obtained.

4.2 Froth height equation

Azbel (1963) showed theoretically that the froth height (hf) above a

perforated plate was a function of Froud number based on clear liquid height on

the assumption of both spherical and elliptical bubbles as follows:

1FrHhf ………………………………………………… (4.4)

Takahashi and Miyahara (1973) showed that froth height above perforated

plate under stagnant liquid flow on the assumption of spherical capped bubble

as follows:

Fr

5

861Hhf ……………………………………………….…… (4.5)

And the experimentally froth height is:

42/1

f 105.8FrFr5.61Hh ………………………………....… (4.6)

43/1

f 105.8FrFr0.21Hh ………………………………... (4.7)

4.3 Dimensional Analyses


Dimensional analysis is used to correlate operating conditions and physical

properties which affect the removal efficiency of oily wastewater in flotation

column.

If removal efficiency (R %) is assumed to be a function of the following

parameters, then :

R% = F (CA, C S, g, Ug, db, L, L, L) …………………………..... (4.8)

The dimensionless groups are obtained using Buckingham's -theorem

(Coulson &Richardson, 1978). The resulting expression then has the form:

R% = C1 (CA/ L)C2

(CS/L)C3

(1/Re)C4

(1/We)C5

(1/Fr)C6

………………...…(4.9)

Therefore the constants C1 and the powers of the dimensions groups in Eq.4.9

were calculated and shown in chapter 5, section 5.5.

Where, Re No. =

Ud, We No. = l Ug

2d/ , Fr No. =

R

g

gd

V.

Chapter Five

Introduction

The results will be presented in five sections. The first will deal with the

effect of hydrodynamic characteristics (bubble diameter, bubble rise velocity, gas

hold up), the second section deals with the effect of various factors on the

removal efficiency (pH, initial oil concentration, gas velocities, additives,

sampling zone, and mixer), the third section deals with the effect of interfacial

area and velocity gradient on the removal efficiency, the fourth section deals with

the best condition for finding the best removal efficiency and the last one deals

with dimensionless groups for removal efficiency and finding an equation for the

removal efficiency.

5.1 Hydrodynamic Characteristics

Hydrodynamic characteristics including bubble diameter, bubble rise velocity,

gas hold-up, were measured and tabulated in Tables E.1 to E.7 in Appendix E.

5.1.1 Bubble Diameter

The relationship of the bubble diameter at the center in the axial direction of

the flotation column at different gas velocities (0.00636 to 0.0636 m/s) of tap

water and oily wastewater at concentration 30ppm are shown in Fig. 5.1. It can

be seen from this figure that increasing gas velocity resulted in an increase in

bubble diameter, that because the breaking and coalescence phenomena. Also it

shows higher bubble diameter in pure water than oily wastewater because the

Results & Discussion

Chapter five: Results and discussion 51

pure water does not contain contaminants like the oily wastewater which affects

the bubble size and rise velocity (Clift et al, 1978).

The effect of hole diameter (2 mm for perforated plate and 120 m for porous

sparger) of the gas distributor on the bubble diameters were shown in Fig. 5.2. It

can be seen that the bubble diameter increased with increasing hole diameter

since the increase in hole diameter resulted in an increase in bubble rise velocity

for a given gas flow rate. These results show that the flotation column operates

within the bubbly flow regime; the present experimental results were projected

on the homogeneous bubbly flow regime map of Shah et al, 1982.

The effect of addition of surfactant on bubble diameters was shown in Figs.

5.3. to 5.7., respectively for different concentration of oily wastewater.

Examining Fig. 5.3., it can be seen that, bubble diameters decreased with

increasing the concentration of sodium laurel sulfate (SLS), while bubbles

diameters slightly decreased with the addition of camper. These phenomena can

be explained by the addition of surfactant to the wastewater which hinders

bubbles coalescence by accumulating at the gas-liquid interface and orienting

their hydrophilic group into the liquid film surrounding the gas bubble and this

creating repulsive electric force when two bubbles come close to each other

(Keital and Onken, 1982). The experimental results show that, when adding

alum not affected because alum has no effect on the surface tension and has no

effect on the bubble size. The size of the bubble was measured when adding alum

found to be in range of (3-3.5) mm at Co=800 ppm.

5.1.2 Bubble Rise Velocity

Bubble rise velocities at different concentrations of surfactant for Co=800

ppm are shown in Fig. 5.8. , and the rise velocity was found experimentally and

also theoretically by using Eq.2.4, where SF equal to one. It can be seen that the

bubble rise velocity decreased with adding surfactants. This decrease is


explained on the basis of surface tension gradient present on the bubble surface

(Davis and Acrivos, 1966), and can be seen that the rise in velocity

experimentally was higher than that found by using Eq.2.4.

The relationship between the bubble rise velocity and the hole diameter of

the gas distributor was shown in Fig. 5.9. It was found that the bubble rise

velocity increased with increasing hole diameter at different gas velocity, that is

because the large bubbles have a small drag force, and also depend on stock's

equation, therefore the rise velocity increased, while the relationship between

bubble rise velocity and different gas velocities was plotted in Fig. 5.10. From

this figure, can be noticed that the bubble rise velocity increased with increasing

gas velocities. Also this Figure shows the results plotted by theoretical Equation

2.4 to compare between the experimental and theoretical results, and also shows

the rise velocity of pure water was higher than oily wastewater, because the

contaminants affect mass transfer via hydrodynamic and molecular effects, and

the contaminants decrease the mobility of the interface so the rise velocity

decreased (Clift et al, 1978).

5.1.3 Gas Hold-up

Gas hold-up was measured by the visual observation of liquid level. The

relationship between gas hold-up and different hole diameter of gas distributor

at different flow rates are plotted in Fig. 5.11. This figure shows that the higher

hole diameter resulted in low gas hold-up for a given volumetric flow rate. This

result is in agreement with Behnoosh et al, 2009 and Mostafa, 2004.

The effect of addition of surfactants on gas hold-up is shown in Fig. 5.12.

From this figure, it can be seen that the gas hold-up increases with increasing

surfactant concentrations. The explanation of this behavior is that adding

surfactant will lead to hinder the bubble coalescence and produce small bubbles

which cause increases in gas hold-up.


Fig. 5.13 shows the values of froth height calculated from Equations 4.4 and

compared with the experimental froth height calculated by using equation 4.6 at

Co=30 ppm, here the hf value calculated from equation 4.4 is larger than that of

equation 4.6 at the same gas velocity.

Figure 5.14 shows the effect of gas velocity on local gas hold up and

compare this value with average gas hold up at the same gas velocity, where the

local gas hold up was measured by using U-tube manometer filled with water. It

can be seen that the local gas hold up increases with increasing gas velocity, but

there values still less than the average gas hold up and a good agreement can be

noticed between the local and average gas hold up.

When these results are compared with air-water system it can be noticed a

very low difference between the local and average gas hold up, that is shown in

Fig.5.15.

0

1

2

3

4

5

6

7

8

9

10

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Gas Velocity (m/sec)

Bu

bb

le D

iam

ete

r (m

m)

Wastewater

Pure water

Figure (5.1): Effect of gas velocity on bubble diameter, H=70 cm and Co= 30 ppm.

Perforated sparger


0

1

2

3

4

5

6

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Gas Velocity(m/sec)

Bu

bb

le S

ize(m

m)

porous

perforated

Figure(5.2): Effect of hole diameter on the bubble size at different gas velocities,

H=70 cm, and Co=30 ppm

0

0.5

1

1.5

2

2.5

3

1 4 7 10 13Surfactant Dose (ppm)

Bu

bb

le D

iam

ete

r (m

m)

SLS

Camper

Figure (5.3) Effect of adding surfactant on the bubble diameter, Q=0.0113(m3/min),

H=70 cm, and Co=100 ppm


0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30

Surfactant Dose (ppm)

Bu

bb

le D

iam

ete

r (m

m)

SLS

Camper

Figure (5.4): Effect of adding surfactant on the bubble diameter, Q=0.0113(m3/min),

H=70 cm, Co=200 ppm

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100


Bu

bb

le D

iam

ete

r (m

m)

SLS

Camper

Figure (5.5): Effect of adding surfactant on the bubble diameter, Q=0.0113(m3/min),

H=70 cm, Co=400 ppm


0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100 120 140


Bu

bb

le D

iam

ete

r (m

m)

SLS

Camper


H=70 cm, Co=600 ppm

0

0.5

1

1.5

2

2.5

3

3.5

0 50 100 150 200


Bu

bb

le D

iam

ete

r (m

m)

SLS

Camper


H=70 cm, Co=800ppm


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 50 100 150 200

Surfactant Dose(ppm)

Bu

bb

le R

ise

Ve

loc

ity

(m

/se

c)

Ub (m/sec) Ex."SLS"

Ub (m/sec) Eq.2.4"SLS"

Ub (m/sec) Ex. "Camper'

Ub (m/sec) Eq.2.4"Camper"

Figure (5.8) Effect of surfactant concentration on bubble rise velocity, H=70cm,

and Co= 800ppm.

0

5

10

15

20

25

30

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Gas Vlocity (m/sec)

Bu

bb

le R

ise V

elo

cit

y (

m/s

ec)

perforated

porous

Figure (5.9): Effect of hole diameter on the bubble rise velocity at different gas

velocities, H=70 cm, and Co=30 ppm


0

0.05

0.1

0.15

0.2

0.25

0.3

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


Bu

bb

le R

ise V

elo

cit

y (

m/s

ec)

Ub (m/sec) Experimental

Ub (m/sec) Eqn.2.4

Puer water

Figure (5.10): Comparison between the experimental and theoretical bubble rise

velocity, H=70cm, Co= 30 ppm.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


Gas H

old

Up

Porous distributor

Perforated plate

Puer water

Figure (5.11): Effect of hole size at different gas velocities on gas hold-up, H=70 cm,

and Co=30 ppm


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 20 40 60 80 100 120 140 160 180


Gas H

old

Up

SLS

Camper

Figure (5.12): Effect of the surfactant concentration on the gas hold-up, H=70cm,

Q=0.0113 m3/min, and Co=800 ppm

0

10

20

30

40

50

60

70

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


Fro

th H

eig

ht

(cm

)

Eqn. (4.4 )

Eqn. (4.6 )

Figure (5.13): Froth height calculated by Equations (4.4) and (4.6), H=70 cm, and

Co=30 ppm


0

0.05

0.1

0.15

0.2

0.25

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


Gas H

old

up

local

average

Figure(5.14): Effect of gas velocity on the local gas hold up, H=70cm, Co=30ppm

0

0.05

0.1

0.15

0.2

0.25

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


Gas H

old

up

local

average

Figure (5.15): Effect of gas velocity on the local gas hold up, H=70cm, air-water

system.


5.2 Effect of Various Factors on the Removal Efficiency of Oily

Wastewater

The effect of various factors on the removal efficiency of emulsified oil

such as pH, initial oil concentration, gas velocity, adding coagulants and

flocculants agents, and the effect of the mixing by stirrer on the removal

efficiency and another parameters. The experimental value are tabulated in

Tables E.8 to E.18 in Appendix E.

5.2.1 Effect of pH

The effect of pH on the removal efficiency of emulsified oil by flotation

column is shown in Fig. 5.16. Plotting the removal efficiency (R %) versus time

at various pH values, obtained by adding an adjustment to the mixture. From

this figure it can be seen that (R%) increases suddenly at the beginning of the

run then the ratio began to increase slowly with time and it was found that the

highest removal is achieved when the pH of the emulsion was about 4.3. This

result is in agreement with the results given by Aneak& Wirach, (2009), they

concluded that oil removal efficiency 97% at the pH (4-7).

The effect of pH on the removal efficiency by adding alum in different

doses is plotted in Fig. 5.17. This figure shows that the removal efficiency at

pH=4 .3 is the highest value at alum dose 560 ppm. The removal rate constant

at various pH was found by plotting against log(C/Co) against time in Fig.5.18.

And their values are tabulated in Table 5.1.


Table (5.1): Rate constants value at different pH

pH K(1/sec)

4.3 0.206

7.2 0.148

8.5 0.057

The rate constant plotted at various pH values shown in Fig.5.18. It can be

seen that the best removal is at pH=4.3, that result is in agreement with

Sulaymon& Mohammed, 1020

5.2.2 Effect of Initial Oil Concentration

The removal rate of oil at various initial oil concentrations (30 to 800 ppm)

was studied and it was found that the removal rate increases with increasing

initial oil concentration that because when the concentration of oil increased the

contact of air bubble and oil droplet was increased. This is shown in Figs. 5.19,

and 5.20(a) which show the relationship between removal efficiency (R%) with

time of flotation at different concentrations (100-800ppm) of oily wastewater.

Also these experimental results are represented in three dimensions curve as

shown in Fig.5.20 (b). This Figure shows the combined effect of time flotation

and concentration of oily wastewater on removal efficiency. Three dimensional

representation in this work is mainly to show the classification of the optimum

surface shape of two parameters which give higher removal efficiency. The

removal rate constants at various initial oil concentrations were found and

plotted log(C/Co) against time in Fig. 5.21. The slope of the lines gives the rate

constants and their values are tabulated in Table 5.2.


Table (5.2): Rate constants at various initial oil concentrations.

Co (ppm) K (1/sec) n

100 0.012 1.05

200 0.0223 0.87

400 0.0446 0.66

600 0.0493 0.51

800 0.177 0.47

It was found that the fastest removal of oil occurred at the highest initial

concentration.

An empirical correlation from the experimental results was found by

computer programming as shown in Eqn.5.1, for initial oil concentration (100-

800), with R2=0.98, to make comparison between the experiment and predicted

results as shown in Fig. 5.22,

R% =0.053Co +33.9 ………………………………………………….… (5.1)

5.2.3 Effect of Gas Velocities on the Removal Efficiency

The removal efficiency of emulsion from wastewater was studied at

different gas velocities (0.00636 to 0.0636 m/sec) in order to show the effect of

gas velocity and air bubble diameter on the removal efficiency of oil. This

effect is shown in Fig. 5.23 by plotting R% versus time at different gas velocity

and from this figure, it can be seen that R% becomes larger at higher gas

velocity that because the higher gas velocity case to increase the collection zone

(collection oil and air bubble) and that cause to increase the froth zone and the

removal efficiency.


The dependence of removal efficiency on bubble diameter is shown in Fig.

5.24(a). From this Figure, it was found that the highest removal efficiency is

obtained at the smallest bubble diameter, the effect of bubble diameter is that

small bubbles have a large projected area which facilitate collision with oil

drops as well as the oil drop is more accessible to the smaller bubble. This

result is in agreement with Jung and Woo, 2004. Fig. 5.24(b) shows the

effectiveness of different parameters (bubble diameter and gas velocity) on each

of them.

5.2.4 Effect of Coagulant and Flocculant Agents

Fig. 5.25 shows the effect of adding sodium laurel sulfate (SLS). It can be

seen that the removal efficiency improves with adding the surfactant.

The explanation of this improvement is that surfactant reduces surface

tension and reduces the bubble diameter and increases the coalescence of larger

diameter droplets which are more easily removed, that result is in agreement

with (Gregory and Zebal, 1990). They concluded that chemical pre-treatment

of oil-water emulsions is based on the addition of chemicals that destroy the

protective action of the emulsifying agent, overcoming the repulsive effects of

the electrical double layers to allow the finally sized oil droplets to form larger

droplets through coalescence.

The removal rate constant at various concentration log(C/Co) versus time is

plotted in Fig.5.26. It can be seen that the rate constant increased with

increasing SLS concentration that result is in agreement with Lima, 2005. Table

5.3 show the value of rate constant and the order of the reaction of each

concentration of the surfactant.


Table (5.3): Rate constants at various surfactant concentrations.

C surfactant(ppm) K n

Zero 0.023 0.96

5 0.207 0.425

10 0.211 0.422

48 0.23 0.385

72 0.24 0.25

96 0.28 0.102

Coagulant Alum with concentration ranged from 80 to 560 ppm was used

alone in the experiment and used in combination with surfactant to show the

effect on the removal efficiency.

Figure 5.27 shows the effect of adding alum to the removal efficiency of

emulsion. This figure shows that R% increased with increasing concentration of

alum, also from Fig. 5.28, it can be noticed that the removal is higher when

adding alum and surfactant together as compared with adding alum alone.

Fig 5.29. Shows the effect of adding alum on COD (Chemical oxygen

demand), it can be noticed that COD decreases slowly without alum compared

with adding alum and also obtaining a good clarification.

Fig. 5.30 shows the effect of adding alum on BOD (Biological oxygen

demand), from the results obtained it can be seen that BOD decreases when

increasing alum dose.


5.2.5 Effect of Sampling Zone

Figs.5.31. and 5.32. show the effect of the sample zone where the sample

was taken at the distance 10 cm from the bottom of column flotation and the

second 25 cm and the third 50 cm through height column flotation. It can be

noticed that at the distance 10 cm, the best removal efficiency was obtained,

compared with 25 and 50 cm. and Fig.5.33 shows the comparison in removal

efficiency at the same sampling zone with and without additive to see the

difference results in each run. In this zone the bubble was very small; therefore

the contact between oil and bubble was good and as a result the removal

efficiency was high.

5.2.6. Effect of Mixing

From above experimental results as induced air flotation by porous

distributor and chemical treatment process by adding Alum and Surfactant were

the effective methods for treating oily wastewater to obtain water as effluent <

10 ppm, this value is accepted by EPA, but to modify this system, then the

flotation bubble column combined with agitator mixer has different speed and

this system is called MIAF, Painmanakul et al, 2010, studied the process and

the results were compared with the results obtained from IAF process and from

the Jar –test experiments.

Figure 5.34. show the effect of different speeds of the stirrer (50-250)

rpm(22.6-253sec-1

) on the gas hold up, where the gas hold up increases when

increasing the speed of the stirrer, Fig.5.35 shows the comparison between the

gas hold up with and without stirrer and found that the gas hold up with stirrer

was higher than without stirrer. This may be due to the formation of larger gas

bubbles where the stirrer plays a vital role in breaking of large bubbles; thereby

increasing the gas hold up, this result is in agreement with Shamugam, 2008


and Fig. 5.36. Show the effect of the mixing on the oil removal efficiency at

different time.

It can be noticed at the range (50-250) rpm that the removal efficiency

increased slowly and the high removal efficiency can be obtained at 200 rpm

and the removal efficiency decreased slowly compared with 200 at 250 rpm.

This system is called (MIAF) and R% in it was higher than (IAF). This result

can be explained that the size of oil droplets increases due to the sweep flocc

coagulation from the presence of alum content and thus accelerates the

separation flotation process. Fig.5.37 shows the effect of stirrer on the bubble

size; also a correlation has been developed as shown in Eqn.5.2 for fractional

gas hold up for stirred flotation column based on computer programming with

statistical method.

g =0.39 (Ug) 0.0163

(H/D) 0.157

(N/L) 0.473

………………………………… (5.2)

The comparison between the observed and the predicated results is shown in

Fig. 5.38, where the average error was 2%, and the correlation coefficient was

0.98.

Figure.5.39 shows a comparison between the removal of oil in the Jar-test

and in the flotation column in the same initial oil concentration equal to 800

ppm and the same dose of additive 24 SLS+80 alum and at 50 rpm, the results

shows that the removal efficiency in the flotation column is higher than the Jar-

test and that is in agreement with Puget&Massrani, 2000.


40

50

60

70

80

90

100

0 500 1000 1500 2000

Time (sec)

R%

pH=7.2

pH=8.5

pH=4.3

Figure (5.16): Effect of pH on the oil removal, Q=0.0113 m3/min, H=70 cm and

Co=800 ppm

60

65

70

75

80

85

90

95

0 100 200 300 400 500 600

Alum Dose (ppm)

R%

pH =7.2

pH =8.5

pH =4.3

Figure (5.17): Effect of adding Alum dose on the oil removal efficiency, H=70 cm,

at different pH, and Co=800 ppm , t=1500 s .


-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0 500 1000 1500 2000

Time(sec)

Lo

g(C

/Co

)

pH=7.2

pH=8.5

pH=4.3

Log.

(pH=7.2)Log.

(pH=8.5)Log.

(pH=4.3)

Figure (5.18): Log(C/Co) versus time at different pH values, Q=0.0113m3/min,

t=1500 sec, and Co=800 ppm, H-70 cm.

30

35

40

45

50

55

60

65

70

75

80

0 200 400 600 800 1000

Oil Concentration (ppm)

R%

Figure (5.19): Effect of the initial oil concentration on the removal efficiency,

pH=7.2, Q= 0.0113 m3/min, t=1500 sec.


0

10

20

30

40

50

60

70

80

0 500 1000 1500 2000Time (sec)

R%

Co =100 ppm

Co= 200 ppm

Co= 400 ppm

Co= 600 ppm

Co= 800 ppm

Figure (5.20) (a): Effect of the initial oil concentration on the removal efficiency,

pH=7.2, Q= 0.0113 m3/min, as function of time.

Figure (5.20) b: Effect of the initial oil concentration on the removal efficiency in a 3D

plot, pH=7.2, Q= 0.0113 m3/min, as function of time.

70

65

60

55

50

45

40


-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 500 1000 1500 2000

Time (sec)

Lo

g(C

/Co

)Co =100 ppm

Co =200 ppm

Co=400 ppm

Co =600 ppm

Co=800 ppm

Log. (Co

=200 ppm)Log. (Co

=100 ppm)Log. (Co=400

ppm)Log. (Co=800

ppm)Log. (Co

=600 ppm)

Figure (5.21): Log(C/Co) versus time at different Co values, Q=0.0113m3/min, t=1500

sec, and Co=800 ppm, H=70 cm.

30

35

40

45

50

55

60

65

70

75

80

30 40 50 60 70 80

Predicted Values

Ob

se

rve

d V

alu

es

Figure (5.22): Comparison between the observed vales of removal efficiency of

oily wastewater and the predicted vales.


40

45

50

55

60

65

70

75

0 500 1000 1500 2000Time (sec)

R%

Ug=0.006363 m/sec

Ug=0.017 m/sec

Ug=0.033 m/sec

Ug=0.044 m/sec

Ug=0.053 m/sec

Ug=0.06363 m/sec

Figure (5.23): Effect of Gas Velocity on the oil removal, H=70 cm and Co=30 ppm,

pH=7.2.

64

65

66

67

68

69

70

71

72

1.3 2 2.7 3.4 4.1 4.8

Bubble Diameter (mm)

R%

Figure( 5.24)(a): Effect of bubble size on the removal efficiency, Co=30 ppm , at

different gas velocities (0.00636-0.0636), pH=7.2 .


Figure( 5.24)(b): Effect of bubble size on the removal efficiency, Co=30 ppm , at

different gas velocities (0.00636-0.0636) 3Dplot, pH=7.2 .

50

55

60

65

70

75

80

0 500 1000 1500 2000

Time (sec)

R%

SLS=Zeor

SLS= 1.5 ppm

Figure (5.25): Effect of adding surfactant on the oil removal efficiency, H =70 cm, and

Co=30 ppm, pH=7.2.

40

35

30

25

20

15

10

5


-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 500 1000 1500 2000

Time(sec)

Lo

g(C

/Co

)5 sls

10 sls

48 sls

72 sls

96 sls

Log. (5

sls)Log. (10

sls)Log. (48

sls)Log. (72

sls)Log. (96

sls)

Figure (5.26): Log(C/Co) versus time at different surfactant dose (ppm),

Q=0.0113m3/min, t=1500 sec, and Co=800 ppm, H=70 cm.

60

65

70

75

80

85

90

95

0 100 200 300 400 500 600

Alum Dose (ppm)

R%

Figure(5.27): Effect of alum dose on oil removal efficiency, Co= 800 ppm, pH =7.2


60

65

70

75

80

85

90

95

100

0 500 1000 1500 2000

Time (sec)

R%

80 Alum+24 SLS

240 Alum +24 SLS

80 Alum+64 SLS

240 Alum+64 SLS

Figure (5.28): Effect of adding alum and SLS together, H=70 cm, pH=7.2 and Co=800

ppm

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 500 1000 1500 2000

Time (sec)

CO

D (

pp

m)

Alum =Zero

Alum= 560 ppm

Figure (5.29): Effect of Alum dose on Chemical oxygen demand, Co=800 ppm

, pH= 7.2.


0

100

200

300

400

500

600

700

0 500 1000 1500 2000

Time (sec)

BO

D (

pp

m)

Alum =Zero

Alum =560 ppm

Figure (5.30): Effect of Alum dose on Biological oxygen demand, Co=800 ppm

, pH= 7.2.

0

10

20

30

40

50

60

70

80

0 500 1000 1500 2000

Time (sec)

R%

X=10 cm

X=25 cm

X=50 cm

Figure (5.31): Effect of the sample zone on the removal efficiency, Co=800 ppm,

pH=7.2, Q= 0.0113 m3/min.


40

50

60

70

80

90

100

0 500 1000 1500 2000

Time (sec)

R%

X=10 cm

X=25 cm

X=50 cm

Figure (5.32): Effect of the sample zone on the removal efficiency, Co=800 ppm,

pH=7.2, and with 64 sls+240 alum, Q= 0.0113 m3/min.

56

61

66

71

76

81

86

91

96

0 500 1000 1500 2000

Time (sec)

R%

w ithout additive

w ith additive

Figure (5.33): Comparison in removal efficiency at X=10, pH =7.2, H=70 cm,

Q=0.0113 m3/min


0.08

0.09

0.1

0.11

0.12

0.13

0.14

0.15

0.16

0.17

0 50 100 150 200 250 300

Speed Of The Stirrer (rpm)

Gas H

old

Up

Figure (5.34): Effect of the speed of the stirrer on the gas hold-up, H=70 cm, Co=800

ppm

0

0.05

0.1

0.15

0.2

0.25

0.3

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


Gas H

old

Up

without stirrer

with stirrer

Figure (5.35): The comparison in gas hold up values, H=70 cm, Co=800 ppm


70

77.5

85

92.5

100

0 500 1000 1500 2000

Time (sec)

R% 50 rpm

100 rpm

150 rpm

200 rpm

250 rpm

Figure (5.36): Effect of the speed of the stirrer on the removal efficiency, pH=7.2,

Q=0.0113 m^3/min, Co=800 ppm , 64 sls+240 alum .

1

1.2

1.4

1.6

1.8

2

2.2

2.4

0 50 100 150 200 250 300

Speed Stirrer (rpm)

Bu

bb

le D

iam

ete

r (m

m)

Figure (5.37): Effect of the speed of the stirrer on the bubble size, H=70 cm, Co=800 ppm


Figure (5.38): Predicted versus observed gas hold up of Eqn.5.2.

65

70

75

80

85

90

95

0 500 1000 1500 2000Time (sec)

R%

Jar -test

Flotation column

Figure (5.39): A comparison between flotation column and the Jar-test, Co=800 ppm


5.3 Effect of Interfacial Area and Velocity Gradient on the Removal

Efficiency

Figure 5.40 shows that the interfacial areas vary between (40.4and 112) 1/m

for IAF and (65.3-143) l/m for MIAF, where the calculation of it was found in

appendix "D" while gas velocities can alter between (0.00636 and 0.0636 m/sec).

It can be noted that the obtained values are corresponded with the number of

bubbles generated and thus the available bubble surface for the interacting with

oil droplets presence in the liquid phase, therefore, these values of (a) roughly

increase linearly with the gas flow rate injected into the flotation column, but the

MIAF system give higher value of (a) than IAF. The small effect of alum

concentrations on the interfacial areas has been again observed as shown

previously in the results obtained with the variation or bubble sizes. Note that, the

values of (a) are directly linked to the bubble diameters, bubble rising velocities

and their formation frequencies, due to the variation of calculated velocity

gradient with gas flow rate as presented in Fig. (5.41). In any flotation

system, the value of G increases linearly with the gas velocities. Their values

vary between (99 and 288)1/sec whereas the gas velocities change between

(0.006363and 0.0636) m/sec; more turbulent mixing condition occurs at higher

gas flow rate. In order to take into account the available bubble surface and also

the mixing condition occurred in the flotation process, the ratio of interfacial area

(a) to velocity gradient (G) was determined and presented in Fig. (5.42). This

figure shows that the ratios of interfacial area (a) to velocity gradient (G) vary

between (0.4 - 0.38) sec/m for IAF and (0.66-0.49) for MIAF while gas flow

rates can change between (0.006363 and 0.0636)m/sec by using porous sparger.

Moreover, it can be seen that the maximum of the a/G values can be found at the

gas flow rate equal to (0.033) m/sec which corresponds to the Ug value that

provides the highest removal efficiency obtained with both IAF and MIAF


processes, therefore, the a/G ratio can be used in order to select the operating

condition of the flotation process.

Note that , the optimal chosen a/G ratio will relate to the gas flow rates that

generate ,not only high interacting opportunity/surface between oil droplets and

bubbles, but also proper mixing condition between generated bubbles, oil

droplets and applied chemical agents in the flotation processes (IAF and MIAF) ,

and thus the highest oily wastewater treatment efficiency, and the relation

between the treatment efficiency and the ratio of interfacial area to velocity

gradient (a/G) is shown in Fig. (5.43). From this figure it can be found that the

treatment efficiencies obtained with IAF and MIAF processes increase roughly

with the a/G values However, at the same a/G value, the differences of removal

efficiencies obtained with the IAF and MIAF processes can be observed. These

confirm that, not only the interacting and mixing phenomena control the overall

removal efficiency, but also the chemical dosages applied in the MIAF process

can affect the associated performances and the experimental value were tabulated

in Tables E.19 to E.26 in Appendix" E".

0

20

40

60

80

100

120

140

160

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


a (

1/m

)

IAF

MIAF

Figure (5.40): Interfacial area versus gas velocity for the IAF and MIAF processes,

Co=30 ppm , t=1500 sec, H=70 cm


0

50

100

150

200

250

300

350

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


G (

1/s

ec

)

IAF

MIAF

Figure (5.41): Velocity gradient versus gas velocity for the IAF and MIAF processes,

Co=30 ppm , t=1500 sec, H=70 cm

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07


a/G

(sec/m

)

MIAF

IAF

Figure (5.42): Ratio of interfacial area to velocity gradient versus gas velocity for the

IAF and MIAF processes, Co=30 ppm , t=1500 sec, H=70 cm


60

62

64

66

68

70

72

74

76

78

80

0.4 0.45 0.5 0.55 0.6 0.65 0.7

a/G (sec/m)

R%

IAF

MIAF

Figure (5.43): Treatment efficiency versus ratio of interfacial area to velocity gradient for

the IAF and MIAF processes.

5.4. The Best Conditions

As results, from the experimental work, the best conditions that give

maximum removal of oil, COD and BOD from wastewater, can be obtained

when the concentration of surfactant is 64ppm, alum is 240ppm with pH 4.2

and by using stirrer with 200 rpm. Then from Figs.5.44, 5.45and 5.46 the oil

concentration, COD, BOD in the treated water are nearest to the Iraqi

regulation for the preservation of water sources (act No.B (2)-2001

amendment). The results are tabulated in E.26, E.27 and E.28 in Appendix

"E", where the standard final oil concentration was <10 ppm, COD <150

ppm and BOD<40 ppm.


0

20

40

60

80

100

120

140

160

0 500 1000 1500 2000

Time(sec)

Fin

al

Oil

Co

ncen

trati

on

(pp

m) MIAF

64 SLS+240 alum

pH=4.2

standared

Figure (5.44): Effect of the best condition on oil removal, Co=800ppm, Ug=0.025m/sec.

0

100

200

300

400

500

600

700

800

900

0 500 1000 1500 2000

Time (sec)

CO

D (

pp

m)

MIAF

pH=4.2

64SLS+240 alum

standared

Figure (5.45): Effect of the best condition on COD, Co=800ppm, Ug=0.025m/sec.


0

50

100

150

200

250

300

350

0 500 1000 1500 2000

Time (sec)

BO

D (

pp

m)

MIAF

pH=4.2

64sls +240 alum

standared

Figure (5.46): Effect of the best condition on BOD, Co=800ppm, Ug=0.025m/sec.

5.5. Dimensionless Groups for Removal Efficiency

Experimental results for different parameters were correlated in the general

dimensionless Eqn.4.9 that is

R% = C1 (CA/ l )C2

(CS/L)C3

(C/Co)C4

(1/Re)C5

(1/We)C6

(1/Fr)C7…..…(4.9)

The coefficient of the equation C1, C2, C3, C4, C5, C6 and C7 are found by

using statistical programming. Values of the coefficient, correlation coefficient,

average absolute error, and variance are listed in Table5.4.

A comparison between the observed and predicted removal efficiency is

shown in Fig. 5.46.


Table (5.4): Constants and statistical analysis results of equation 5.2 for removal efficiency

Coefficient Value Coefficient Value Coefficient Value coefficient value

C1 1.67 C3 161 C5 1.48 C7 1.096

C2 145.7 C4 0.0624 C6 1.56

Average absolute error (A.A.E) =0.053%, Correlation coefficient=0.9999 ,

Variance=0.95.

Figure( 5.46): Predicted versus observed removal efficiency

Where the range of Re (43.4-90.9), We (0.013-0.025), Fr (0.0199-0.0425).

Chapter Six

6.1. Conclusions

6.1.1 Separation of Oil

The emulsified oil with concentration (30-800 ppm) can be removed by

dispersed air flotation; high percentage was achieved from 20 to 25 minutes.

Induced air flotation (IAF) and modified induced air flotation (MIAF) were

applied and analyzed in term of treatment efficiency; the removal efficiency

obtained with IAF processes was smaller than obtained in MIAF.

Bubble size increases with the increase in air flow rate, and the size of bubble

decrease with adding surfactant.

Adding alum and (SLS) together have a high coagulant effect than adding them

individually.

The best removal efficiency was found at pH 4.3.

The gas hold up increased with the increase of gas velocity and also increased

when adding surfactant, when using the stirrer. The gas hold up was correlated

according to the following equation:

g =0.39 (Ug) 0.0163

(H/D) 0.157

(N/L) 0.473

The ratio of interfacial area to velocity gradient (a/G) has been proved to be the

important parameter to consider for attaining a good performance in the

treatment of oily wastewater process.

The kinetics of flotation bubble column was studied and it was found that the

removal rate constant (K) increases with increasing oil concentration and with

dosage surfactant (SLS). Also the experimental results indicate that the order of

the kinetic flotation nearly changes between half to first order.

Conclusions & Recommendations

for future work

Chapter six: Conclusions & Recommendations for future work 89

A correlation for the removal efficiency was correlated and found acceptable

values between the experiment and observed value:

R% = 1.67 (CA/ l )145.7

(CS/L)161

(C/Co)0.0624

(1/Re)1.48

(1/We)1.54

(1/Fr)1.096

6.2 Recommendations for future work

1. Studying the oily wastewater treatment by membrane.

2. Using two or three columns in order to enhance the removal efficiency.

3. Studying the effect of temperature.

4. Using more active surfactant from recent papers and research.

5. Comparison between IAF and DAF.

6. Treatment of the oily wastewater by IAF, but in continuous operation.

7. Effect of two contaminants on the removal efficiency.

Calibration curves of the flow meters AAppendix

201

y = 0.9022x + 0.0004

R2 = 0.9964

0

0.005

0.01

0.015

0.02

0.025

0.03

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

Reading scale(m^3/min.)

Flo

wm

ete

r re

ad

ing

(m^

3/m

in.)

Figure ِ A.1: Calibration Curve of gas Rotameter

Calibration curves of the flow meters AAppendix

201

mixer Calibration curves of the BAppendix

301

y = 47.143x - 30.143

R2 = 0.9554

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6 7 8

Gage Control

Sp

ee

d(r

pm

)

Figure ِ B.1 Calibration Curve of mixer by digital tachometer

0

50

100

150

200

250

300

0 50 100 150 200 250 300

Speed (r.p.m.)

G (

1/s

ec

)

Velocity Gradient (G) at Various Speeds Figure B.2

mixer Calibration curves of the BAppendix

301

Distributor design cAppendix

401

This procedure was developed by Ruff et al. (1978) to ensure the flow

through all the openings of perforated plates for fluid dispersion. If all the

perforations of a perforated plate for dispersing a gas or liquid in a liquid

phase are occupied by the disperse, weeping, backflow etc. can occur, which

are usually undesirable. In bubble column Reactors plates are frequently

used with perforations of diameters 1 to 5mm. Ruff (1978) has investigated

perforated plates with perforation of diameters 0.3 to 1mm in the gassing of

liquids to find what minimum gas velocity in the perforations is necessary to

ensure complete flow through the openings of the sieve plates. He found that

at small perforation diameters a constant Weber number must be maintained,

while, at large perforation diameters a Froude number must be maintained in

order to ensure flow through openings or prevent weeping. The effect of the

fractional free area of the perforations varied over the range from 0.1 to 5%.

We=2 and Fr=0.37 give the minimum velocity of the disperse required in the

perforations, and significant weeping is to be prevented in the case of large

perforations.

Following steps are used to find the number of holes required to

ensure flow through all the perforations and to prevent weeping of the

continuous phase. The calculations are based on the following physical

properties:

w=993.8 Kg/m3, g=1.16 Kg/m

3, w=0.0728 N/m, Perry and Chilton

(1978).

Step 1:

Calculation of the diameter do according to eqn. (C-1):


401

8/52/1

32.2

gw

g

g

wo

gd

………………………………… (C-1)

8/52/1

16.18.993(

16.1

81.9*16.1

0728.0(32.2

od

do=0.0027 m

do=2.7 mm.

The perforation diameter selected lies below this value of do and so criterion

We= constant must be used.

Step 2:

We have:

2

2

w

oog UdWe

……………………………………………. (C-2)

og

wo

dU

22

3

2

10*0.1*16.1

)0728.0(*2

oU

oU 11.1m/sec

Applying a safety factor of 40% gives:

oU 16.65 m/sec

oo

gc

Ud

UdN ……………………………………………….. (C.3)

Ug=Upper range of experimental gas velocity

=0.063 m/sec

68.15)001.0(

063.0)1.0(2

2

N

70N


401

Free area=area of holes area of distributor

=2

2

c

o

d

Nd

=2

2

)1.0(

70)001.0( =0.007 =0.7%

This value lies between the range of (0.1 – 5) %


401

Calculations Sample of Appendix D

701

D.1. Local Gas Hold up

The particle case of gas-slurry will be considered. To make the

solution tractable it is assumed that the dynamic component of the

pressure is negligible and that the bubble are lightly, and

consequently the bubble-particle aggregate density is negligible. The

pressure above atmospheric at A and B Fig. D.1. (a) (Finch &Dobby,

1990):

PA = sl LA g (1- g gA) ………………………………… (D.1)

PB = sl LB g (1- g Gb) …………………………… ……… (D.2)

Where sl is the slurry density, and g s, g B are the gas hold up above A and B

respectively (the product L (1- g ) is the equivalent height of the slurry without

gas). Therefore, the pressure difference between A and B, the pressure

difference is:

P = sl L g (1- g ) …………………………………………… (D.3)

Where g is the gas holdup between A and B. Upon rearranging, g is

given by

g = 1- (P /sl L g) …………………………………………………. (D.4)

Note that g is measured locally over distance L and that gas holdup in other

parts of the column is not a factor. By repeating the measure at intervals along a


701

column, the profile of g with height can be established. If water-filled

manometers are used to measure pressure .Fig. D.1. (b).

PA = w g (L+h1)

PB = w g h2

Therefore

P = w g (L-h)

Where h is positive when the upper manometer level is higher than the lower

manometer level then g is given by:

g =1-(w/sl)(1-h/L) …………………………………………(D.5)

Assumed w=sl eq. (D.5) then reduces to

g = h/L


701

Fig. D.1. Measuring gas holdup by pressure difference: (a) general; (b) using

manometers.

D.2. Sample of Calculation

D.2.1 average gas holdup

For Ug 0.0636, HL=70cm, HF=86.1

Eg =F

LF

H

HH

(86.1-70)/70=0.23

D.2.2 Bubble Rise Velocity

sec/206.02.1

25.0

time

distencemU b


770

D.2.3 Local Gas Holdup

At Ug=0.0636 m/sec, then E local =5/35=0.14

D.2.4 Calculation of Interfacial Area (a) and Velocity Gradient (G)

(a)= FB *( Hl/Ub ) *( Sb/Vtotal)

For flow rate 0.000048 m3/sec, Vb 10

-8 m

3, Sb 0.000025 m

2 Ub

from the experimental 14.7 m/sec and Hl 0.7 m

Where Fb =flow rate /Vb = 4000 sec-1

, therefore the value of (a)

equal to 40.4 m-1

for IAF.

For MIAF at the same flow rate Vb 4*10-8

m3, Sb 0.000013 m

2,

Fb 11461 sec-1

, Ub 0.26 m/sec therefore the value of (a) 65.3 m-1

Now for finding (G) value for both IAF and MIAF where:

G = P/ ( *V)0.5

P = 3904* flow rate * log (3904+10.33)/10.33

P= 0.48 m3/sec

V (liquid volume in column) =0.0055 m3

(G) = 99 sec-1

Tables Figures Appendix E

111

Table (E.1): Effect of Gas Velocity on Bubble

Characteristics.

Ug

(m/s)

db

(mm)

Ub

(m/s)

Experiment

Ub

(m/s)

Theoretical

εg

(-)

εglocal

(-)

0.00636 1.4 0.147 0.083 0.056 0.02

0.017 2.1 0.159 0.101 0.085 0.028

0.033 2.4 0.166 0.108 0.14 0.055

0.044 2.8 0.175 0.12 0.18 0.085

0.053 3.4 0.1888 0.13 0.22 0.11

0.06363 4.3 0.206 0.15 0.25 0.14

Table (E.2): Effect of surfactant (sls) concentration on

bubble Characteristics.

Co CS db

(mm)

Ub

(m/s)

Experiment

Ub

(m/s)

Theoretical

εg

(-)

εglocal

(-) 100 1.5 2 0.1624 0.11 0.086 0.08

100 3.5 1.88 0.151 0.106 0.1 0.086

100 5 1.72 0.1457 0.099 0.11 0.087

100 8 1.55 0.144 0.093 0.12

0.087

100 12 1.34 0.129 0.084 0.15 0.088

200 3 2.2 0.15 0.106 0.085 0.072

200 7 1.87 0.146 0.099 0.12 0.086


111

200 10 1.81 0.137 0.096 0.13 0.088

200 16 1.62 0.135 0.088 0.135 0.089

200 24 1.44 0.127 0.083 0.2 0.09

400 12 2.3 0.1512 0.106 0.085 0.081

400 32 2.13 0.1483 0.102 0.093 0.085

400 48 2 0.1433 0.099 0.1 0.089

400 64 1.97 0.1398 0.098 0.114 0.1

400 80 1.94 0.1376 0.097 0.13 0.1

600 18 2.5 0.161 0.11 0.084 0.083

600 48 2.4 0.158 0.108 0.093 0.084

600 72 2.3 0.155 0.106 0.1 0.09

600 96 2.2 0.153 0.104 0.12 0.1

600 120 1.8 0.1512 0.099 0.13 0.1

800 24 2.7 0.1607 0.115 0.086 0.083

800 64 2.31 0.1527 0.106 0.099 0.09

800 96 2.24 0.1515 0.105 0.12 0.095

800 128 2.14 0.1496 0.103 0.135 0.1

800 160 2.11 0.147 0.102 0.14 0.11


111

Table (E.3): Effect of surfactant (camper) concentration on

bubble Characteristics.

Coil Ccamper db

(mm)

Ub

(m/s)

Experiment

Ub

(m/s)

Theoretical

εg

(-)

εglocal

(-) 100 1.5 2.45 0.0144 0.098 0.087 0.086

100 3.5 2.2 0.14 0.096 0.11 0.088

100 5 2

0.135 0.092

0.12 0.09

100 8 1.78

0.131 0.087 0.13

0.099

100 12 1.45 0.124 0.081 0.2 0.1

200 3 2.31 0.15 0.104 0.089 0.086

200 7 2 0.145 0.096 0.11 0.089

200 10 1.88 0.1411 0.09 0.12 0.09

200 16 1.73 0.1354 0.085 0.12 0.09

200 24 1.56 0.1282 0.082 0.19 0.1

400 12 2.8 0.168 0.12 0.055 0.03

400 32 2.5 0.16 0.11 0.057 0.029

400 48 2.3 0.1544 0.106 0.062 0.042

400 64 2.1 0.1513 0.101 0.077 0.06

400 80 1.99 0.1485 0.098 0.086 0.056

600 18 2.8 0.168 0.12 0.055 0.03

600 48 2.5 0.161 0.11 0.057 0.029

600 72 2.3 0.1547 0.106 0.062 0.042

600 96 2 0.1508 0.101 0.077 0.056

600 120 1.98 0.148 0.098 0.086 0.056

800 24 2.9 0.165 0.119 0.06 0.05


111

800 64 2.5 0.158 0.11 0.062 0.051

800 96 2.43 0.159 0.109 0.065 0.054

800 128 2.33 0.155 0.107 0.072 0.066

800 160 2.12 0.15 0.102 0.075 0.068

Table (E.4): Effect of Hole Diameter on Bubble

Characteristics at Liquid Height= 70cm.

Ug

(m/s)

do

(mm)

db

(mm)

Ub

(m/s)

εg

(-)

εglocal

(-)

0.00636 0.12 1.4 14.7 0.056

0.044

0.017 0.12 2.1 15.9 0.085

0.053

0.033 0.12 2.4 16.6 0.14

0.09

0.044 0.12 2.8 17.5 0.18

0.1

0.053 0.12 3.4 18.88 0.22

0.11

0.0636 0.12 4.3 20.6 0.25

0.15

0.006363 2 1.7 15.2 0.05

0.029

0.017 2 3 17.75 0.07

0.057

0.033 2 3.5 18.8 0.1

0.061

0.044 2 4.2 20.66 0.14

0.11

0.053 2 5.25 23 0.19

0.14

0.0636 2 9.4 25.7 0.23

0.153


111

Table (E.5): Effect of gas velocity on the froth height.

Ug

(m/s)

hf(m)

Eq.(4.4)

hf(m)

Eq.(4.6)

0.006363 2.32 3.34

0.017 6.79 9

0.033 13.7 20.6

0.044 20.7 30.6

0.053 35.6 51.3

0.0636 45.78 64.3

Table (E.6): Effect of the gas velocity on both average and

local gas hold up in air-water system.

Ug

(m/s)

εg

(-)

εg local

(-)

0.006363 0.029 0.05

0.017 0.057 0.07

0.033 0.11 0.11

0.044 0.15 0.15

0.053 0.2 0.2

0.0636 0.23 0.23


111

Table (E.7): Effect of gas velocity on bubble diameter,

H=70cm, Co=30 ppm.

Table (E.8): Effect of pH on the oil removal efficiency,

Ug=0.025 m/s, do= 0.12 mm and H=70 cm.

Time

(sec)

Removal efficiency (%)

pH=4.3 pH=7.5 pH=8.5

300 72 63 60

600 84 69 62

900 84.9 71 68

1200 86.67 74.5 72.3

1500 88.5 75 73.5

1800 88.49 76 73.8

Gas

velocity

(m/sec)

db

(mm) wastewater

db

(mm) pure water

0.0636 1.4 1.7

0.017 2.1 3

0.033 2.4 3.5

0.044 2.8 4.2

0.053 3.4 5.25

0.0636 4.3 9.4


111

Table (E.9): Removal efficiency of oil at difference gas

velocity, H=70cm, Co=30 ppm.

Time

(sec)


Ug

(m/s)

0.00636

Ug

(m/sec)

0.017

Ug (m/s)

0.033

Ug

(m/s)

0.044

Ug

(m/s)

0.053

Ug (m/s)

0.0636

300 46 65.3 63.22 64.55 64.7 69.3

600 51 65.8 67.11 67.7 65.66 69.6

900 58.6 66.8 67.7 68.4 66.4 70.4

1200 64 67.4 68.3 69 69 71.1

1500 64.44 68.33 69.33 69.5 69.8 71.5

1800 62.4 67.33 69.33 68.6 69.55 71.1

Table (E.10): Effect of alum dose on Chemical oxygen

demand, Co=800ppm, pH=7.2

Time

(sec)

COD (ppm) BOD(ppm)

Alum =zero

Alum =560ppm

Alum =zero

Alum =560

300 1835 1204 655 429

600 1830 915 653 326

900 1541 722 550 257

1200 1228 578 438 206

1500 1204.5 524 429 153

1800 1156 525 412 147


111

Table (E.11): Effect of sampling zone on the removal

efficiency, pH=7.2, Co=800ppm, without additive.

Time

(sec)


X=10

(cm)

X=25

(cm)

X=50

(cm)

300 62 60 40

600 65 61 55

900 68 65 61

1200 71 66 63

1500 72.5 68 65

1800 72.3 70.4 68.7

Table (E.12): Effect of sampling zone on the removal

efficiency, pH=7.2, Co=800ppm, with 64sls+240alum.

Time

(sec)


X=10

(cm)

pH=7.5

(cm)

pH=8.5

(cm)

300 72 69 67

600 81 77 72

900 87 82.34 80.11

1200 92 84 81.12

1500 93.9 88 85.6

1800 93.8 90 87.44


111

Table (E.13): Effect of the speed of the stirrer on the

hydrodynamic characteristics, Co=800ppm, H=70cm.

Speed

stirrer

(rpm)

εg

(-)

db(mm) Ub(m/sec)

50 0.11 2.2

0.149

100 0.12 2.17

0.146

150 0.14 1.97

0.144

200 0.15 1.81

0.14

250 0.16 1.85

0.141

Table (E.14): Effect of speed stirrer on the removal

efficiency, pH=7.2, Ug=0.025m/sec, Co=800ppm, 64

sls+240 alum

Time

(sec)

R (%)

50

(rpm)

100

(rpm)

150

(rpm)

200

(rpm)

250

(rpm)

300 85 80 83 88 82

600 88 86.5 88 92.11 84

900 93 90 91.2 93.8 92

1200 93.86 92.4 92.8 96 92.8

1500 94 94.86 95 98.8 95.7

1800 94 94.8 95.34 98.6 95.9


111

Table (E.15):.Effect of alum dose on oil removal efficiency

at different pH

Alum

dose

(ppm)


pH=4.3 pH=7.5 pH=8.5

80 74 69 75.5

240 85 72 86

320 87 74.5 88.6

400 88 77 89.5

560 88 79.4 89.87

Table (E.16): Effect of surfactant concentration on the

removal efficiency, pH=7.2, Co=100ppm, Ug=0.025m/sec.

Time

(sec)


SLS=zero SLS=1.5

300 63.2 72.8

600 67.11 73.2

900 67.7 74.5

1200 68.3 75.3

1500 69.33 76.5

1800 69.33 76.3


111

Table (E.17):.Effect of adding alum and sls together on the

removal efficiency, Co =800ppm, Ug =0.025m/sec

Time

(sec)

R (%)

80alum+24sls 240alum+24sls 80alum+64sls 240alum+64sls

300 75 85 81 84

600 86 90 87 91

900 89 92 91 92

1200 90 92.34 91.99 92.6

1500 92.5 93 94 95

1800 92.33 93.23 94 95.22

Table (E.18): Effect of initial oil concentration on the

removal efficiency.

Time

(sec)

R (%)

100(ppm) 200(ppm) 400(ppm) 600(ppm) 800(ppm)

300 31 33 37 51 62

600 31.8 34.4 41 62 68

900 33 36.8 44 66 71

1200 36.5 38 49 67.5 74.5

1500 42 44 52.8 69 75

1800 42.5 44.7 52.9 69.3 76


111

Table (E.19): Effect of gas velocity on interfacial area for

IAF and MIAF, Co=800ppm.

Gas

velocity

(m/sec)

a (m-1)

IAF MIAF

0.00636 40.4 65.3

0.017 71.9 88.7

0.033 108.5 134.8

0.044 109.7 140

0.053 111.8 141

0.0636 112 143

Table (E.20): Effect of gas velocity on velocity gradient for


Gas

velocity

(m/sec)

G(sec-1)

IAF MIAF

0.00636 99 99

0.017 165.34 165.34

0.033 222 222

0.044 247 247

0.053 286.7 286.7

0.0636 288 288


111

Table (E.21): Effect of gas velocity on interfacial

area/velocity gradient for IAF and MIAF, Co=800ppm.

Gas

velocity

(m/sec)

a/G (sec/m)

IAF MIAF

0.00636 0.408 0.66

0.017 0.43 0.54

0.033 0.488 0.6

0.044 0.44 0.56

0.053 0.38 0.49

0.0636 0.38 0.49

Table(E.22): Effect of a/G on the removal efficiency for


a/G

(sec/m),IAF R%,

a/G

(sec/m),MIAF

R%

0.408 64 0.66 73

0.43 67.4 0.54 74.4

0.488 68.3 0.6 75

0.44 69 0.56 76.3

0.38 69.8 0.49 76.7

0.38 71 0.49 78.4


111

Table ( E.23): Effect of treatment process on the removal

efficiency, Co=800ppm, Ug=0.025m/sec, pH=7.5.

Time

(sec)

R (%)

Flotation column Jar test

300 75 69

600 79.3 73.4

900 88 75

1200 91 79.33

1500 92.9 80.5

1800 92.87 80.4

Table (E.24): Comparison in removal efficiency at X=10,

pH =7.2, H=70 cm, Ug=0.025 m/sec

Time

(sec)

R (%)

Without additive With additive

300 62 72

600 65 81

900 68 87

1200 71 92

1500 72.5 93.9

1800 73.3 93.8


111

Table(E.25): Effect of speed stirrer on the gas hold up, Ug=

(0.00636-0.0636), Co=30ppm, pH=7.5.

Gas

velocity

(m/sec)

Hold up (%)

Without stirrer With stirrer

0.00636 0.056 0.07

0.017 0.082 0.089

0.033 0.14 0.15

0.044 0.18 0.19

0.053 0.22 0.24

0.0636 0.25 0.28

Table (E.26): Effect of the best conditions on the final oil

concentration.

Time

(sec)

Final oil concentration(ppm)

MIAF 64sls+240alum pH=4.2

300 75.2 128 136

600 63.12 72 104

900 49.6 64 96

1200 32 59.2 68.8

1500 9.6 40 48

1800 11.2 39 45.6


111

Table( E.27): Effect of the best conditions on BOD.

Time

(sec)

Final BOD (ppm)


300 161.6 275.2 292

600 135 154.8 223

900 106.6 137 206

1200 68.8 127 147

1500 20 86 103

1800 24 83.8 98

Table (E.28): Effect of the best conditions on COD.

Time

(sec)

Final COD (ppm)


300 452 770 818

600 380 433 626

900 298 385 578

1200 192 356 414

1500 57 240 289

1800 67 234 274

في العراق التي تستتهك كماتات كراترن ت المهمةالشركات إحدى( كركوك)في شركه نفط الشمال

. الزراعاتةحدوث تكوث كرار في المساحات إلىويؤدي الشركةالماء المكوث بالنفط يتصرف هذن , الماء

ت لات ل تيناته التفويتم لكمتاء كاماويته-ةبمعالجتات فازياويت كفتونانظمه لدراسةالهدف هذا العمل هو

وعمكاته التدياتر ( MIAF)وكتذل عمكاته ربتط بتا ( IAF)هتي المستتدد ةتيناه التفويم . المكوث بالنفط

قفترن التدالاكي )عمود التفويتم بواسفةالشغل العمكي لمعالجه الماء المكوث بالنفط تم . وعمل يارنه بانهم

و واستتدد وهو ثابت لا ل إجراء العمكاات سم 01دالال العمود وارتفاع السائل (سم 051سم وطوله 01

ألمييره نوع السارا ا والياناة( كم2)وبيفر ( ثيب01) ألمييره المعدناة أليفعهنوعا وزع الغاز

وعمتود تفويتم فتور استتعمل الدت ط أفضتلالحصول عكى لاكط ولأجل(. ايكر تر 021) ناعمةثيوب

لكغتتاز وكتتذل استتتعمكت ألموقعاتته ألحجماتته النستترةواستتتعمل المتتانو اتر لياتتا . الدقايتتةبدورن (51-251)

لكفتتاء المدتكفتتةلكمتغاتترات التتتيثارات. الفياعتتةوحجتتم الفياعتتةلياتتا ستترعه العالاتتة الستترعةالكتتا ارا تات

ثتتا / (1.10.0-1.110.0)الفصتتل لكمتتاء المكتتوث بتتالنفط يتتل الدتتوان الهادروداينماكاتته يتتل ستترعه الغتتاز

والدالتتةالشتتب وأضتتافهلكشتتد الستتفحي الدافضتتةوتركاتتز المتتواد جتتزء بتتالمكاو (011-1.)وتركاتتز التتنفط

.تم دراستها بالدقايةدورن (251-51)وسرعه الد ط (0.5-..3)الحا ضاه

المتتواد . لكغتتاز ألحجماتته والنستترة الفياعتتةوستترعه وتتعود الفياعتتةالدتتوان الهادرودينا اكاتته تتضتتم حجتتم

عالجته المتاء المكتوث بتالنفط . دتكفتة يجترع( لكشتد الستفحي الدافضتةالشتب والمتواد ) المضتافة تعمكةالمس

لكتتل تت التتنفط الفصتتل كفتتاء إ بانتتت الدراستتة .الدتت ط باستتتعمالدرستتت لعمتتود التفويتتم وحتتدن وكتتذل

الحا ضتاه والدالتة( لكشتد الستفحي الدافضتةالشب والمواد ) المضافةتعود لجرعه المواد BODو CODو

ووجتد ا عتدل التفويتم يتزداد باستتعمال الشتب . وسرعه الغتاز والتركاتز اتبتتدائي لكتنفط وتتاثار الدت ط

وكتذل ..3الحا ضتاه الدالتةوجتد عنتد ا تكتو الأسترعوالمعتدل . لكشتد الستفحي ستوية الدافضتةوالمواد

جتتزء 01نفط المتريتتي اقتتل التت% )80كفتتاء الفصتتل تصتتل . دور بالدقايتتة 211 بستترعةاستتتعمال الدتت ط

.جزء بالمكاو 011عند ا يكو التركاز اتبتدائي ( بالمكاو

د بزياد تركاتز التنفط وجترع المتواد الدافضتة ايزد و لا ل عمكاة التفويم وجد إ ثابت عدل الإزالة

.لكشد السفحي ووجد إ عدل التفويم يتغار النص لكواحد

برهنتت ( G)عمكاا لا ل العوا ل الهادرودينا اكاة لكفياعة وانحتدار السترعةوجدت ( a)المساحة الراناة

.الأبعاد يكت برسو ات ثنائاه وث ثاة العمكاةالنتائج . عكى عمكاة تفويم كفوء لكسافر كررا اتر هم

:الحجماة لكغاز ووجدت عند التفويم المفور وهي كالتالي لكنسرة تجريره ع قةوجدت

الخلاصة

g =0.39 (Ug) 0.0163

(H/D) 0.157

(N/L) 0.473

.عكى التوالي 1.80و% 2وكانت الع قة بمعدل لافا فكق و عا ل ارتراط

:هي( dimensionless) بع قة للإزالةوالع قة العا ة

R% = 1.67 (CA/ l )145.7

(CS/L)161

(C/Co)0.0624

(1/Re)1.48

(1/We)1.54

(1/Fr)1.096

.1.8888و عا ل ارتراط % .1.15بمعدل لافا هذن الع قة وجدت

هيدروديناميكية على عملية ال تأثير الخواص التطويف للماء الملوث بالنفط

رسالة مقدمة الى

الجامعة التكنولوجية كجزء من متطلبات –قسم الهندسة الكيمياوية تكرير / الدراسة لنيل درجة ماجستير علوم في الهندسة الكيمياوية

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اعـــــداد

محمدشهد سالم

2012

وزارة التعليم العالي والبحث العلمي

الجامعة التكنولوجية

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effect of hydrodynamic characteristics on flotation

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