A

report on

Anaerobic Process in Industrial Wastewater Treatment

Master of Technology

in

Environmental Engineering

Under the guidance of

Dr. Athar Hussain

HOD CIVIL

School of engineering

Gautam Buddha University

Submitted by-

14EEN 001 ABHISHEK SINGH KHEVARIYA

14EEN 002 AVANEESH KUMAR

14EEN 004 NITIN YADAV

14EEN 005 SANJAY KUMAR

CERTIFICATE

This is certify that the report entitled “Anaerobic Process in Industrial Wastewater

Treatment” is submitted by Abhishek Singh Khevariya, Avaneesh Kumar, Nitin

Yadav and Sanjay Kumar for the project in Master of Technology (Environmental

Engineering) submitted to Gautam Buddha University, Greater Noida.

This matter embodied in this report is original & has not been submitted earlier.

Date: 13 / 12/ 2014

Mr Athar Hussain

HOD

(CIVIL DEPARTMENT)

CONTENTS

Certificate (ii)

Abstract (v)

Introduction Inorganic Industrial Wastewater Treatment 01

Organic Industrial Wastewater Treatment 02

Literature review

Sources of Industrial Wastewater Treatment 03

Anaerobic Treatment 07

Aerobic Treatment 07

Difference between Aerobic & Anaerobic Process 08

Anaerobic Fermentation 09

Aerobic Respiration 10

Process Microbiology

Fermentative Bacteria 11

Acetogenic 11

Homoactegenes 12

Methenogenes 13

Factors Affecting Anaerobic Process

Temperature 14

pH Control 15

Nutrients 15

Toxicity 15

Retention Time 16

Feeding Strategy 16

Agitation Strategy 16

Types of Anaerobic Reactors

Anaerobic Filter Bed Reactors 17

Anaerobic Contact Process Reactors 18

Anaerobic Fluidized Bed Reactors 18

UASB 18

Design of Anaerobic Reactors

Conditions 20

Design Parameters 20

Design Procedure 22

Advantages of Anaerobic Process 24

Limitations of Anaerobic Process 25

Applications in the Industries 26

Bibliography 27

ABSTRACT

The motivations for treatment of wastewater are manifold. Treatment

and reuse of wastewater conserves the supply of freshwater and this

presents clear advantages with respect to environmental protection. The

main objective of this project report was to study Anaerobic Process in

Wastewater Treatment Process.

Anaerobic Process is a biological process that can degrade waste

organic material by the concerted action of a wide range of

microorganisms in the absence of oxygen. The process consists of a

complex series of reactions that convert a wide array of polymeric

substances such as carbohydrates, proteins, and lipids, having carbon

atoms at various oxidation and/or reduction states, to one-carbon

molecules in its most oxidized state (CO2) and its most reduced state

(CH4).

1 Anaerobic Process in Industrial Wastewater Treatment

INTRODUCTION

During the last century a huge amount of industrial wastewater was discharged into

rivers, lakes and coastal areas. This resulted in serious pollution problems in the water

environment and caused negative effects to the eco-system and human’s life.

Until the mid-18th century, water pollution was essentially limited to small, localized

areas. Then came the Industrial Revolution, the development of the internal combustion

engine, and the petroleum-fuelled explosion of the chemical industry. With the rapid

development of various industries, a huge amount of fresh water is used as a raw

material, as a means of production (process water), and for cooling purposes. Many

kinds of raw material, intermediate products and wastes are brought into the water

when water passes through the industrial process. So in fact the wastewater is an

"essential by-product” of modern industry, and it plays a major role as a pollution

sources in the pollution of water environment.

There are many types of industrial wastewater based on different industries and

contaminants; each sector produces its own particular combination of pollutants.

Generally, industrial wastewater can be divided into two types: inorganic industrial

wastewater and organic industrial wastewater.

Inorganic industrial wastewater

Inorganic industrial wastewater is produced mainly in the coal and steel industry, in the

nonmetallic minerals industry, and in commercial enterprises and industries for the

surface processing of metals (iron picking works and electroplating plants).

These wastewaters contain a large proportion of suspended matter, which can be

eliminated by sedimentation, often together with chemical flocculation through the

addition of iron or aluminum salts, flocculation agents and some kinds of organic

polymers. The purification of warm and dust-laden waste gases from blast furnaces,

converters, cupola furnaces, refuse and sludge incineration plants, and aluminum works

results in wastewater containing mineral and inorganic substances in dissolved and un-

2 Anaerobic Process in Industrial Wastewater Treatment

dissolved form. Other wastewater from rolling mills contain mineral oil and require

additional installations, such as scum boards and skim-off apparatus, for the retention

and removal of mineral oils. Residues of emulsified oil remaining in the water also need

chemical flocculation. In many cases, wastewater is produced in addition to solid

substances and oils, and also contains extremely harmful solutes. These include blast-

furnace gas-washing wastewater containing cyanide, wastes from the metal processing

industry containing acids or alkaline solutions (mostly containing non-ferrous metals and

often cyanide or chromate), wastewater from eloxal works and from the waste gas

purification of aluminum works, which in both cases contain fluoride.

Organic industrial wastewater

Organic industrial wastewater contains organic industrial waste flow from those

chemical industries and large-scale chemical works, which mainly use organic

substances for chemical reactions. The effluents contain organic substances having

various origins and properties. These can only be removed by special pretreatment of

the wastewater, followed by biological treatment. Most organic industrial wastewaters

are produced by the following industries and plants: pharmaceuticals, cosmetics,

organic dye-stuffs, glue and adhesives, soaps, synthetic detergents, pesticides and

herbicides, Tanneries and leather factories.

Industrial wastewater treatment covers the mechanisms and processes used

to treat waters that have been contaminated in some way

by anthropogenic industrial or commercial activities prior to its release into the

environment or its re-use.

3 Anaerobic Process in Industrial Wastewater Treatment

LITERATURE REVIEW

SOURCES OF INDUSTRIAL WASTEWATER

Various sources of Industrial wastewater are listed in the table below –

1. Iron and steel Industry: The production of iron from its ores involves

powerful reduction reactions in blast furnaces. Cooling waters are inevitably

contaminated with products especially ammonia and cyanide. Production

of coke from coal in coking plants also requires water cooling and the use of

water in by-products separation. Contamination of waste streams includes

Sector Pollutants

Iron & Steel BOD, COD, Oil, Metal, Cyanide, Phenols &

Acids

Textile & Leather BOD, Solids, Sulfates & Chromium

Pulp & Paper BOD, COD, Solids, Chlorinated Organic

Compound

Petrochemical & Refineries BOD, COD, Phenols & Chromium

Chemicals COD, Heavy Metals, Cyanide, SS

Non- Ferrous Metal Fluoride & SS

Microelectronics COD & Organic Chemicals

Mining Metal, SS, Acids & Salts

4 Anaerobic Process in Industrial Wastewater Treatment

gasification products such as benzene, naphthalene, cyanide,

ammonia, phenols, cresols together with a range of more complex organic

compounds known collectively as polycyclic aromatic hydrocarbons (PAH). Wastewaters include acidic rinse waters together

with waste acid. Although many plants operate acid recovery plants (particularly

those using hydrochloric acid), where the mineral acid is boiled away from the

iron salts, there remains a large volume of highly acid ferrous sulfate or ferrous

chloride to be disposed of. Many steel industry wastewaters are contaminated by

hydraulic oil, also known as soluble oil.

2. Mines and quarries: The principal waste-waters associated

with mines and quarries are slurries of rock particles in water. These arise from

rainfall washing exposed surfaces and haul roads and also from rock washing

and grading processes. Volumes of water can be very high, especially rainfall

related arising on large sites. Some specialized separation operations, such

as coal washing to separate coal from native rock using density gradients, can

produce wastewater contaminated by fine particulate hematite and surfactants.

3. Pulp and paper Industry: Effluent from the pulp and paper

industry is generally high in suspended solids and BOD. Standalone paper mills

using imported pulp may only require simple primary treatment, such

as sedimentation or dissolved air flotation. Increased BOD or chemical oxygen

demand (COD) loadings, as well as organic pollutants, may require biological

treatment such as activated sludge or up flow anaerobic sludge blanket reactors.

For mills with high inorganic loadings like salt, tertiary treatments may be

required, either general membrane treatments like ultrafiltration or reverse

osmosis or treatments to remove specific contaminants, such as nutrients.

5 Anaerobic Process in Industrial Wastewater Treatment

4. Textile Industry: Dye bath wastewater generated by textile mills is

often rated as the most polluting among all industrial sectors. The pollution load

is characterized by high color content, suspended solids, salts, nutrients and

toxic substances such as heavy metals and chlorinated organic compounds.

Many textile mills in the state currently discharge their wastewater to local

wastewater treatment plants with minimum treatment such as pH neutralization.

This process removes much of the residual dye color. Larger mills can discharge

more than 2 million gallons of wastewater of this kind per day.

5. Petrochemical Refineries: Refineries can generate a significant

amount of wastewater that has been in contact with hydrocarbons. Wastewater

can also include water rejected from boiler feed water pretreatment processes (or

generated during regenerations). Wastewater can also refer to cooling tower

blow downstream, or even once-through cooling water that leaves the refinery.

Once-through cooling water typically does not receive any treatment before

discharge. Cooling tower blow down water and wastewater from raw water

treating may or may not receive treatment at the wastewater treatment plant

(WWTP) before discharge. Contaminated wastewater is typically sent to either a

wastewater treatment plant that is located at the facility, or it can be pretreated

and sent to the local publicly owned treatment works or third-party treatment

facility for further treatment. Water that has not been in direct contact with

hydrocarbons or which has only minimal.

6 Anaerobic Process in Industrial Wastewater Treatment

7 Anaerobic Process in Industrial Wastewater Treatment

INDUSTRIAL WASTEWATER TREATMENT PROCESS

AEROBIC TREATMENT: Organic material decomposing with oxygen is an

"aerobic" process. When organisms that use oxygen feed upon organic matter, they

develop cell protoplasm from the nitrogen, phosphorus, some of the carbon, and other

required nutrients. Carbon serves as a source of energy for organisms and is burned up

and respired as carbon dioxide (CO2). Since carbon serves both as a source of energy

and as an element in the cell protoplasm, much more carbon than nitrogen is needed.

Generally, organisms respire about two-thirds of the carbon they consume as CO2,

while the other third is combined with nitrogen in the living cells.

In nature, the aerobic process is most common in areas

such as the forest floor, where droppings from trees and animals are converted into

relatively stable organic matter. This decomposition doesn’t smell when adequate

oxygen is present. We can try to imitate these natural systems when we plan and

maintain our landscapes. As we learn more about the biology and chemistry of

composting, we can actually hasten the decomposition process.

ANAEROBIC TREATMENT: Anaerobic process is a collection of

processes by which microorganisms break down biodegradable material in the absence

of oxygen. The process is used for industrial or domestic purposes to manage waste

and/or to produce fuels. Much of the fermentation used industrially to produce food and

drink products, as well as home fermentation, uses anaerobic digestion.

Anaerobic digestion occurs naturally in some soils and in lake and oceanic basin

sediments, where it is usually referred to as "anaerobic activity". The digestion process

begins with bacterial hydrolysis of the input materials. Insoluble organic polymers, such

as carbohydrates, are broken down to soluble derivatives that become available for

other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon

dioxide, hydrogen, ammonia, and organic acids. These bacteria convert these resulting

8 Anaerobic Process in Industrial Wastewater Treatment

organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon

dioxide. Finally, methanogens convert these products to methane and carbon dioxide.

The methanogenic archaea populations play an indispensable role in anaerobic

wastewater treatments.

Difference between Anaerobic & Aerobic Process:

Anaerobic Aerobic

Biomass yield

Organic loading rate

Low biomass yield:0.05-0.15 kg VSS/kg COD High biomass yield:0.35-0.45 kg VSS/kg COD

(Biomass yield is not constant but depends on types of substrates metabolized)

(Biomass yield is fairly constant irrespective

of types of substrates metabolized)

Specific substrate utilization rate

High rate: 0.75-1.5 kg COD/kg VSS-day Low rate: 0.15-0.75 kg COD/kg VSS-day

Long start-up: 1-2 months for mesophilic Short start-up: 1-2 weeks

High loading rates:10-40 kg COD/m3-day Low loading rates:0.5-1.5 kg COD/m

3-day

SRT

Longer SRT is essential to retain the slow

growing methanogens within the reactor SRT of 4-10 days is enough for the activated sludge process

Start-up time

9 Anaerobic Process in Industrial Wastewater Treatment

ANAEROBIC PROCESS

Anaerobic treatment is a biological process carried out in the absence of O2 for the

stabilization of organic materials by conversion to CH4 and inorganic end-products such

as CO2 and NH3.

Anaerobic Fermentation

In anaerobic fermentation, there is no external electron acceptor. The product

generated during the process accepts the electrons released during the breakdown of

organic matter. Thus, organic matter acts as both electron donor and acceptor. The

process releases less energy and the major portion of the energy is still contained in the

fermentative product such as ethanol.

Through this method, a cell is able to regenerate nicotinamide adenine dinucleotide

(NAD+) from the reduced form of nicotinamide adenine dinucleotide (NADH), a

molecule necessary to continue glycolysis. Anaerobic fermentation relies on enzymes to

add a phosphate group to an individual adenosine diphosphate (ADP) molecule to

produce ATP, which means it is a form of substrate-level phosphorylation. This

contrasts with oxidative phosphorylation, which uses energy from an established proton

gradient to produce ATP. There are two major types of anaerobic fermentation: ethanol

Anaerobic processes

Anaerobic fermentation Anaerobic respiration

10 Anaerobic Process in Industrial Wastewater Treatment

fermentation and lactic acid fermentation. Both restore NAD+ to allow a cell to continue

generating ATP through glycolysis.

Anaerobic Respiration

Anaerobic respiration on the other hand requires external electron acceptor. The

electron acceptors in this case could be SO42-, NO3

- or CO2. These terminal acceptors

have smaller reduction potentials than O2, meaning that less energy is released per

oxidized molecule. The energy released under such a condition is higher than anaerobic

fermentation. In order for the electron transport chain to function, an exogenous final

electron acceptor must be present to allow electrons to pass through the system. In

aerobic organisms, this final electron acceptor is oxygen. Molecular oxygen is a highly

oxidizing agent and, therefore, is an excellent acceptor. Anaerobic respiration is,

therefore, in general energetically less efficient than aerobic respiration.

Anaerobic respiration is used mainly by prokaryotes that live in environments devoid of

oxygen. Many anaerobic organisms are obligate anaerobes, meaning that they can

respire only using anaerobic compounds and will die in the presence of oxygen.

11 Anaerobic Process in Industrial Wastewater Treatment

PROCESS MICROBIOLOGY

The anaerobic degradation of complex matter is carried out by a series of bacteria.

There exists a coordinated interaction among these microbes. The process may fail if

certain of these organisms are inhibited.

TYPES OF BACTERIA ON THE BASIS OF PROCESS

MICROBIOLOGY

Fermentative bacteria: This group of bacteria is responsible for the

first stage of anaerobic digestion - hydrolysis and acidogenesis. Fermentation bacteria

are anaerobic, but use organic molecules as their final electron acceptor to produce

fermentation end-products. Streptococcus, Lactobacillus, and Bacillus, for example,

produce lactic acid, while Escherichia and Salmonella produce ethanol, lactic acid,

succinic acid, acetic acid, CO2, and H2.

Fermenting bacteria have characteristic sugar fermentation patterns, i.e., they can

metabolize some sugars but not others. For example, Neisseria meningitidis ferments

glucose and maltose, but not sucrose and lactose, while Neisseria gonorrhoea ferments

glucose, but not maltose, sucrose or lactose. Such fermentation patterns can be used to

identify and classify bacteria. The anaerobic species belonging to the family of

Streptococcaceae and Enterobacteriaceae and to the genera of Bacteroides,

Clostridium, Butyrivibrio, Eubacterium, Bifidobacterium and Lactobacillus are most

common.

Hydrogen producing acetogenic bacteria: Acetogenic bacteria

are a specialized group of strictly anaerobic bacteria that are ubiquitous in nature.

Together with the methane‐forming archaea they constitute the last limbs in the

anaerobic food web that leads to the production of methane from polymers in the

12 Anaerobic Process in Industrial Wastewater Treatment

absence of oxygen. Acetogens are characterized by a unique pathway, the Wood–

Ljungdahl pathway of carbon dioxide reduction with the acetyl‐CoA synthase as the key

enzyme. This pathway also allows chemolitho-autotrophic growth on hydrogen and

carbon dioxide and it is the only pathway known that combines carbon dioxide fixation

with adenosine triphosphate (ATP) synthesis. Thus, it is considered the first biochemical

pathway on earth. ATP is synthesized by a chemi-osmotic mechanism with Na+ or H+ as

coupling ion, depending on the organism. In cytochrome‐free acetogens, energy is

conserved by reduction followed by dependent Na+ (or H+) translocation across the

membrane (Rnf complex). Acetogens may represent ancestors of the first bio

energetically active cells in evolution.

CH3CH2COO - CH3COO - + CO2 + H2

Homoacetogenes: The homoacetogens are much more adaptable

than methanogens because in addition to being autotrophic they can also live

as chemoheterotrophs. Clostridium aceticum and Acetobacterium woodii are the two

homoacetogenic bacteria isolated from the sludge.

In the heterotrophic growth mode they can ferment glucose and derive some ATP by substrate level phosphorylation. In so doing they generate carbon dioxide and hydrogen which can then be used to power the chemiosmotic mechanism which allows them to derive some ATP also by anaerobic respiration.

The overall stoichiometry of this growth mode of homoacetogens is shown below.

13 Anaerobic Process in Industrial Wastewater Treatment

Methanogens: Methanogens are autotrophic archebacteria that use anaerobic

respiration for ATP synthesis. Methanogens use CO2 taken up from their growth

environment as the carbon substrate for growth. They use some CO2 as the ultimate

oxidizing agent of an electron transport chain which, by a chemiosmotic mechanism,

maintains a transmembrane electrochemical ion gradient which powers ATP

production. Methanogens use this hydrogen and this process maintains a lowered

hydrogen partial pressure in the reticulo-rumen. Some of the hydrogen producing

heterotrophic microorganisms show altered patterns of metabolism because of

methanogen usage of the hydrogen they produce.

Methanogens affect the growth of some but not all hydrogen producing species of

microorganism in the reticulo-rumen. The equation shows the reduction of CO2 by H2 to

produce methane. This redox reaction sustains anaerobic respiration which allows the

production of ATP.

The methane produced by reduction of the carbon dioxide is lost from the reticulo-

rumen by eructation. It is a waste of feed carbon because the rumen does not have

methanotrophic bacteria and the host ruminant cannot utilize this gas.

14 Anaerobic Process in Industrial Wastewater Treatment

FACTORS AFFECTING ANAEROBIC PROCESS

The successful operation of anaerobic reactor depends on maintaining the

environmental factors close to the comfort of the microorganisms involved in the

process. They are as follows-

1. Temperature: Anaerobic processes like other biological processes operate

in certain temperature ranges. Mesophilic (25-450C) and thermophilic (45-650C)

anaerobic digestion are commonly applied in the field. Most full-scale anaerobic

digesters are operated at mesophilic temperature. Since wastewater and bio

solids is discharged at relatively low temperature (e.g., 18 0C), recent research

toward anaerobic treatment under psychrophilical condition becomes attractive.

For instance, microbial communities involved in digestion are sensitive to

temperature changes. The rate of anaerobic degradation of organic substrates

generally increases in the order of psychrophilic, mesophilic and thermophilic

digestion.

15 Anaerobic Process in Industrial Wastewater Treatment

2. pH Control: pH is an important factor for keeping functional anaerobic

digestion. A typical pH is in the range of 6.5-7.6. The accumulation of

intermediate acids leads to pH drop during fermentation. In order to maintain

stable operation, it is necessary to add bicarbonate or carbonate as an alkalinity

buffer to neutralize volatile fatty acids and carbon dioxide.

3. Nutrients: Macronutrients are the elements that the cellular material of the

anaerobic microorganisms comprises, including hydrogen, nitrogen, oxygen,

carbon, sulfur, phosphorus, potassium, calcium, magnesium and iron. Normally,

anaerobic microorganisms require these elements presented with a

concentration around 10-4

M. In addition to the micronutrients, a number of other

elements, such as Ni and Co must be present in small amount, i.e. below10-4

M.

This is because that these elements are important for the growth of anaerobic

organisms. For example, Ni is necessary for activating factor F430

, which is a co

factor involved in methanogenesis. But it can be inhibitory for fermentative as

well as methanogens if it is present in high concentration.

4. Toxicity: Besides ammonia and nitrate/nitrite, heavy metals, such as Zn, Cu

and Cd can be toxic to acidogenic bacteria. However, many of these elements

and compounds can be tolerated in relatively high concentration due to

absorption in inert material contained in the reactor.

16 Anaerobic Process in Industrial Wastewater Treatment

5. Retention Time: For the CSTR reactors, which are the most prevailingly

used types of reactors, hydraulic and solid retention time is the same. Retention

time is an important operational parameter that is easy to operate and control.

Tremendous efforts have been put into the research of the effect of retention time

on anaerobic digestion. Biologically, only those who are doubling time are shorter

than the retention time can be kept in the reactor, so retention time is one of the

best parameter to be manipulated for separating and enriching different groups of

the microbes involved in the anaerobic process. Also, retention time determines

the time that substrates can be attacked by the enzymes in the reactor.

6. Feeding Strategy: Practically, anaerobic reactors treating sewage sludge

in wastewater treatment plants are fed semi-continuously instead of continuously.

Feeding frequency determines the ratio of food to microbe (F/M) when the

retention time and the working volume have been fixed. Normally, the ratio can

be satisfied so that there is no negative effect on the stability and on the

performance of the anaerobic reactors.

7. Agitation Strategy: It is normally believed that agitation is necessary to

help the diffusion of substrate and increase their contacts with the microbes,

especially when raw sludge is intermittently fed into the reactor. Agitation

strategy can affect anaerobic digestion of sewage sludge and optimum agitation

strategy should be found. In addition, it was also found that mixing levels might

be used as an operational tool to stabilize unstable anaerobic reactor.

17 Anaerobic Process in Industrial Wastewater Treatment

TYPES OF ANAEROBIC REACTORS

There are five principal process variants which are proper in anaerobic wastewater

treatment. These are as follows:

Anaerobic Filter Reactor: The anaerobic filter is similar to a trickling filter in

that a biofilm is generated on media. The bed is fully submerged and can be operated

either upflow or down flow. As wastewater flows through the filter, particles are trapped

and organic matter is degraded by the active biomass that is attached to the surface of

the filter material.

With this technology, suspended solids and BOD removal can be as high as 90%, but is

typically between 50% and 80%. Nitrogen removal is limited and normally does not

exceed 15% in terms of total nitrogen (TN).

Anaerobic filters are usually operated in upflow mode because there is less risk that the

fixed biomass will be washed out. The water level should cover the filter media by at

least 0.3 m to guarantee an even flow regime. The hydraulic retention time (HRT) is the

most important design parameter influencing filter performance. An HRT of 12 to 36

hours is recommended. The ideal filter should have a large surface area for bacteria to

grow, with pores large enough to prevent clogging. The surface area ensures increased

contact between the organic matter and the attached biomass that effectively degrades

it. Ideally, the material should provide between 90 to 300 m2 of surface area per m3 of

occupied reactor volume. Typical filter material sizes range from 12 to 55 mm in

diameter. Materials commonly used include gravel, crushed rocks or bricks, cinder,

pumice, or specially formed plastic pieces, depending on local availability.

18 Anaerobic Process in Industrial Wastewater Treatment

Anaerobic Contact Process Reactor: This process can be considered as

an anaerobic activated sludge because sludge is recycled from a clarifier or separator to

the reactor. Since the material leaving the reactor is a gas-liquid-solid mixture, a

vacuum Degasifier is required to separate the gas and avoid floating sludge in the

clarifier. Here a set of reactors are created in series, often with recycling. This recycled

material is pumped up into the bottom of the first reactor, an upflow reactor. The upflow

anaerobic process is a large reactor which allows the waste to flow up from the bottom

and separates the waste into 3 zones. At the very top is the biogas zone where the gas

is collected. Bacteria digest waste in the lowest portion of the upflow reactor;

the bioreactor zone. In between these two stages is the clarifier zone where the which

exports the stabilized waste.

Fluidized Bed Reactor: This reactor consists of a sand bed on which the

biomass is grown. Since the sand particles are small, a very large biomass can be

developed in a small volume of reactor. In order to fluidize the bed, a high recycle is

required. In this type of reactor, a fluid (gas or liquid) is passed through a granular solid

material (usually a catalyst possibly shaped as tiny spheres) at high enough velocities to

suspend the solid and cause it to behave as though it were a fluid. This process, known

as fluidization, imparts many important advantages to the FBR. As a result, the fluidized

bed reactor is now used in many industrial applications.

Upflow Anaerobic Sludge Blanket Reactor: Under proper conditions

anaerobic sludge will develop as high density granules. These will form a sludge blanket

in the reactor. The wastewater is passed upward through the blanket. Because of its

density, a high concentration of biomass can be developed in the blanket. The UASB

reactor is a methanogenic (methane-producing) digester that evolved from the clarifier.

A similar but variant technology to UASB is the expanded granular sludge bed (EGSB)

digester.

19 Anaerobic Process in Industrial Wastewater Treatment

UASB uses an anaerobic process whilst forming a blanket of granular sludge which

suspends in the tank. Wastewater flows upwards through the blanket and is processed

(degraded) by the anaerobic microorganisms. The upward flow combined with the

settling action of gravity suspends the blanket with the aid of flocculants. The blanket

begins to reach maturity at around 3 months. Small sludge granules begin to form

whose surface area is covered in aggregations of bacteria. In the absence of any

support matrix, the flow conditions create a selective environment in which only those

microorganisms, capable of attaching to each other, survive and proliferate. Eventually

the aggregates form into dense compact biofilms referred to as "granules".

Schematic diagrams of anaerobic wastewater treatment processes: (a) anaerobic filter reactor; (b)

anaerobic contact reactor; (c) fluidized-bed reactor; (d) upflow anaerobic sludge blanket (UASB).

20 Anaerobic Process in Industrial Wastewater Treatment

DESIGN OF ANAEROBIC REACTORS

Conditions for efficient anaerobic treatment –

DESIGN PARAMETERS

Anaerobic Filter:

Width to diameter ratio of reactor =2-6(usually)

Height of reactor =2-12 m(usually)

Hydraulic retention time =20-30 d(for domestic wastewater)

Volumetric loading =0.2-0.8 kg COD/m3 –d

Specific area for the media =100 m2/m3 of volume

• Enough nutrients (N & P) and trace metals especially, Fe, Co, Ni, etc.

COD - N: P = 350:7:1 (for highly loaded system) 1000:7:1 (lightly loaded system)

• Avoid excessive air/O2 exposure

• No toxic/inhibitory compounds present in the influent

• Maintain pH between 6.8 –7.2

• Sufficient alkalinity present (mainly bicarbonates)

• Low volatile fatty acids (VFAs)

• Temperature around mesophilic range (30-38 o

C)

• SRT/HRT >>1 (use high rate anaerobic reactors)

21 Anaerobic Process in Industrial Wastewater Treatment

Fluidized Bed Reactor:

Up –flow velocity =2.0 m/h

Specific area of media =10000 m2/m3 of media volume

Void space =50%

Organic loading =4-5 kg COD/m3-d

Anaerobic Contact Process:

Up-flow velocity =15-20 m/h

Rector depth =3-6 m

Volumetric loading =10-30 kg COD/m3.d

Reactor biomass =15000-20000 mg MLVSS/L

HRT =3-6 h

UASB:

Up-flow velocity =0.5-0.9 m/h

Volumetric loading =6-20 kg COD/m3.d

HRT =6-48 hr

MLSS concentration (i) at the bottom of reactor =100000-150000 mg/l

(ii) at the top of reactor =5000-4000 mg/l

Reactor depth = 3-5 m (for domestic water)

Biomass production =0.2-0.5 m3/kg of COD removed

22 Anaerobic Process in Industrial Wastewater Treatment

DESIGN PROCEDURE

a) Design based on volumetric organic loading rate (VOLR)

VOLR: Volumetric organic loading rate (kg COD/m3-day)

So : Wastewater biodegradable COD (mg/L)

Q : Wastewater flow rate (m3/day)

V : Bioreactor volume (m3)

b) Design based on hydraulic loading rate

H : Reactor height (m)

a : Allowable hydraulic retention time (hr)

Q : Wastewater flow rate (m3/h)

A : Surface area of the reactor (m2)

23 Anaerobic Process in Industrial Wastewater Treatment

,

24 Anaerobic Process in Industrial Wastewater Treatment

ADVANTAGES OF ANAEROBIC PROCESS

• Less energy requirement as no aeration is needed.

• Energy generation in the form of methane gas.

• Less biomass (sludge) generation.

• Less nutrients (N & P) required.

• Application of higher organic loading rate.

• Space saving.

• Ability to transform several hazardous solvents.

25 Anaerobic Process in Industrial Wastewater Treatment

LIMITATIONS OF ANAEROBIC PROCESS

• Long start-up time.

• Long recovery time.

• Specific nutrients/trace metal requirements.

• More susceptible to changes in environmental conditions.

• Effluent quality of treated wastewater.

• Treatment of high protein & nitrogen containing

wastewater.

26 Anaerobic Process in Industrial Wastewater Treatment

APPLICATIONS OF ANAEROBIC PROCESS

(INDUSTRIES)

• Alcohol production

• Brewery and Winery

• Sugar processing

• Starch (barley, corn, potato, wheat, tapioca)

• Waste from textile industry.

• Food processing

• Bakery plant

• Pulp and paper

• Dairy

• Slaughterhouse

• Petrochemical waste

27 Anaerobic Process in Industrial Wastewater Treatment

BIBLIOGRAPHY

en.wikipedia.org/wiki/AnaerobicProcess

books.google.com

Metcalf and Eddy, 1981. Wastewater Engineering:

Collection and pumping of Wastewater. McGraw Hill

Inc., New York.

Research Paper- Anaerobic Treatment of Industrial Effluents, by Mustafa Evren Ersahin, Istanbul Technical University, Turkey.

Research Paper- ANAEROBIC DIGESTION TECHNOLOGY FOR INDUSTRIAL WASTEWATER TREATMENT by Medhat M. A. Saleh and Usama F. Mahmood, El Azhar Univ., Egypt.