CIV 264 - Lecture

Introduction to Environmental Engineering

Kodwo Beedu Keelson Msc Env Eng

MODULE CONTENTS

Microbial Processes

Reactor Hydraulics

Water Quality Parameters

Microbial Processs

CONTENTS

Role of microorganisms

Biological conversions in treatment plants

Bacteria (most important in wastewater treatment)

Algae

Fungi

Protozoa

Types of Microorganisms

The removal of carbonaceous BOD, nitrogen, phosphorous

and the stabilization of organic matter are accomplished

biologically by using a variety of microorganisms, mainly

bacteria

The microorganisms convert the colloidal and dissolved

carbonaceous organic matter into cells, more or less

degraded organic compounds, various minerals and gases

The cells in the suspended sludge can be removed from the

treated liquid by gravity settling, because cells have a

specific gravity greater than that of water.

Role of Microorganisms

Energy and carbon are both required for the

maintenance of the cell and for the synthesis of new

cellular material

Autotrophic organisms use inorganic carbon as carbon

source it is called autotrophic.

Heterotrophic organisms use organic carbon as carbon

source

Energy and Carbon Sources for Microorganisms

Biological growth

Hydrolysis

Decay

Conversions in Biological Treatment Plants

Bacteria are only able to utilize very small and simply

built molecules directly for growth

Acetic acid, ethanol, methanol, propionic acid, glucose

and ammonium, nitrate etc.

Bigger molecules have to be hydrolyzed first

Biological Growth

Conversion of large molecules into small, directlydegradable molecules

The hydrolysis process is a slow process compared tothe biological growth process

Therefore, the hydrolysis will often be the rate-limitingstep in biological wastewater processes

Hydrolysis can be described as a first order process

Hydrolysis

Slowly biodegradable material is released and then

hydrolyzed to soluble substrate

Soluble substrate is used by the viable biomass for

growth, yielding new cell material

Decay of biomass is described as a first order process

with respect to the biomass concentration

Decay

Reactors

MODULE CONTENTS

Reaction Kinetics

Reactor Vessels

Reaction Kinetics

Zero Order Reaction Kinetics

Rate of reaction is independent of proportional to

the concentration of reactant

Occurs in reactions in which a catalyst comes into

plays a part

dC/dt = K

First Order Reaction Kinetics

Rate of reaction is proportional to the concentration

dC/dt = -Kc

k is the first order reaction rate constant (1/T)

c is the concentration (M/L3)

Reactions in water and wastewater treatment plants

are assumed to follow first order reaction kinetics

Second Order Reaction Kinetics

Reactions involving two species A and B

dCA/dt = -KCACB

dCB/dt = -KCACB

k is the second order reaction rate constant (L3/T.M)

Reaction Vessels

What is a reactor vessel?

Any natural water body or artificial tank or enclosure

that receives and discharges water

Biogeochemical transformations occur in reactors

such that the effluent has characteristics different

from the influent

Fully mixed tank

Plug-flow

Types of Reactor

Influent concentration (Cin)

Effluent concentration (C)

Residence time (tR)

Reaction rate constant (k)

Volumetric loading rate (v)

Reactor Variables

Reactor volume (V)

Flow rate (Q)

Reactor liquid depth (D)

Dispersion factor (d)

Surface loading rate (s)

Characteristics of Fully-mixed Tanks

Influent is mixed instantly and completely

Uniform concentration in tank = Concentration in outflow

Treatment Efficiency in Fully-mixed Tanks

Characteristics of Plug-flow Tanks

Long tank of small cross-section

There is little or no longitudinal mixing of the influent

Uniform concentration in tank is different from outflow

Treatment Efficiency in Plug-flow Tanks

Non-ideal Flow in Reactors

Short circuiting - density currents, wind-driven currents

can cause flow to go directly from inlet to outlet, by

passing much of the tank volume

Dead zones Short circuiting - density corners, stagnant

zones, swirling eddies are parts of tank not contributing

much to treatment, shortening effective detention time

Water Quality Parameters

MODULE CONTENTS

Physical Water Quality Parameters

Chemical Water Quality Parameters

Biological Water Quality Parameters

The term water quality relates to all the constituentsof water including both dissolved substances andany other substances carried by the water.

Water pollution may be defined as the presence inwater of impurities in such quantities and of suchnature as to impair the use of the water for a statedpurpose.

The concentration of the pollutant is given by theexpression c = Mass/Volume. usually expressed inmg/L

What is Water Quality?

All receiving waters can assimilate wastes to some extentdepending on the natural selfpurification capacity

Water quality problems or issues arise when the pollutantloads exceed this capacity

Water quality parameters makes it possible to assessextent of water pollution and hence water/wastewatertreatment methods

3 types of water quality parameters physical, chemical,biological

Significance of water quality parameters

Physical Water Quality Parameters

Physical parameters define those

characteristics of water that respond to the

senses of sight, touch, taste, or smell.

Parameters that fall into this category include

suspended solids, colour, taste, odour,

temperature, turbidity

Physical Water Quality Parameters

Categories of solids

Type of Solid Size (m) Specific Gravity

Gross > 6000 0.9 1.2

Grit > 150 2.6

Suspended 0.45 1.4 2.0

Dissolved < 0.45 -

Gross sanitary solids also known as aesthetic, refractory orintractable solids include faecal matter, toilet paper, sanitarypads and condoms.

The particular concern about gross solids these solids istheir aesthetic impact when they are discharged into waterbodies.

Grit which is also called sewer sediment includes sand,gravel and any other solids that have higher specific gravitythan organic biodegradable solids.

The problems associated with grit include partial or totalblockage of pipes which leads to a loss of hydraulic capacity.

Gross solids and Grit

The total suspended solids (TSS) content is the organic andinorganic solid matter which is maintained in suspension, andretained when the sample is filtered (0.45 m pore size)

The retained filter material that can be volatized and burnedoff when ignited at 500C is classified as volatile

Volatile solids, VS, are presumed to be organic matter andfixed solids, FS, is the inert residue

The ratio of VS to FS, typically, 70%, is used to characterizewastewater with respect to the amount of organic matterpresent

Suspended and Dissolved solids

The total suspended solids (TSS) is used

to measure the quality of wastewater

Total suspended solids

Turbidity is a measure of the light-transmittingproperties of water

Turbidity is used to indicate water quality withrespect to colloidal and residual suspendedmatter

Turbid water is aesthetically displeasing

Turbidity measurements are usually made onclean water

Turbidity

Pure water is colourless, but water in nature is often

coloured by foreign substances.

Water whose colour is partly due to suspended matter is

said to have apparent color.

Colour contributed by dissolved solids that remain after

removal of suspended matter is known as true colour

True colour may be measured in potable water analysis

Colour

The terms taste and odour are themselves definitive ofthis parameter.

Substances that produce an odour in water will almostinvariably impart a taste.

However, there are many mineral substances thatproduce a taste but no odour.

Odours produced by organic substances may pose morethan a problem of simple aesthetics, since some of thosesubstances may be carcinogenic.

The taste and odour parameter is associated with potablewater

Taste and Odour

Temperature is not typically used to evaluate directlyeither potable water or wastewater.

It is, however, one of the most important parameters innatural surface-water systems.

The temperature of surface waters governs to a largeextent the biological species present and their rates ofactivity.

Temperature also has a pronounced effect on solubilityof gases.

Wastewater is typically warmer than the local watersupply because of warm wash water and industrialcontributions

Temperature

Chemical Water Quality Parameters

The chemical parameters refer to those parameters

associated with the solvent capabilities of water

Parameters that fall into this category include total

dissolved solids, alkalinity, hardness, organics and

nutrients (nitrogen and phosphorus)

Chemical Water Quality Parameters

This refers to the material remaining in water after

filtration for suspended solids analysis (0.45 m pore

size)

Dissolved solids may be organic or inorganic in nature

Dissolved solids may produce odour, taste and colour in

water

TDS is used in analysis of water and wastewater

Total dissolved solids

Alkalinity is defined as the quantity of ions in water that

will react to neutralise hydrogen ions

Alkalinity is the measure of the ability of water to

neutralise acids

Main constituents of alkalinity include hydroxides (OH-),

carbonates (CO32-), bicarbonates (HCO3

-)

Alkalinity is used in analysis of natural waters to

determine buffering capacity

Alkalinity

Hardness is defined as the concentration of multivalentmetallic cations in solution

Hardness is classified as carbonate hardness andnoncarbonated hardness, depending upon the anionswith which it associates

Carbonate hardness in the hardness that is equivalentto the alkalinity

Noncarbonated hardness refers to any hardness inexcess of the carbonated hardness

Analysis for hardness is made on natural waters and onwaters intended for potable supplies and certainindustrial uses

Hardness

Organic compounds in water are unstable and arereadily oxidized either biologically or chemically

End products include such as carbon dioxide, nitrates,sulphates and water

Decomposition of organic matter in wastewater bymicro-organisms consumes dissolved oxygen (DO)

An indirect indication of the amount of organic materialin wastewater can be derived from the BOD,COD, TOCtests

Organics

Biochemical Oxygen Demand (BOD) - indicates the amount

of oxygen required by aerobic micro-organisms to

decompose the organic matter in a sample of water in a

defined time period e.g. 5 days

Chemical Oxygen Demand (COD) measures the oxygen

equivalent of organic matter that can be oxidized by a string

oxidizing agent e.g. potassium dichromate

Total Organic Carbon (TOC) measures the total organic

content of a compound

Tests for Organics

Phosphorus is an aquatic plant nutrient

Phosphorus can contribute to eutrophication and

reduction of dissolved oxygen

Phosphorus can be expressed as total, organic or

inorganic (ortho- and poly-) phosphorus

Most of the phosphorus occurring in wastewater is in

the inorganic form

Phosphorus

Nitrogen is also an aquatic plant nutrient that cancontribute to eutrophication and reduction of dissolvedoxygen

Nitrogen exists in four main forms: organic nitrogen,ammonia nitrogen, nitrite and nitrate

The term total nitrogen is used to refer to the sum of allthese forms in a sample of wastewater

Organic and ammonia nitrogen make up most of thetotal nitrogen in wastewater

Nitrogen

Biological Water Quality Parameters

This refers to those parameters associated with the absenceor presence of aquatic organisms in a given body of water

Aquatic organisms range in size and complexity from thesmallest single-cell microorganism to the largest fish

Based on their known tolerance for a given pollutant, certainorganisms can be used as indicators of the presence ofpollutants

A body of water hosting large numbers of species with wellbalanced numbers of individuals (species-diversity) isconsidered to be a healthy system

Pathogens present in aquatic environments are capable ofinfecting, or transmitting diseases to humans

Biological Water Quality Parameters

Bacteria

Viruses

Protozoa

Helminths (worms)

Types of Pathogens

Bacteria are single-celled microorganisms,usually colorless

Bacteria are the lowest form of life capable ofsynthesizing protoplasm from the surroundingenvironment

Gastrointestinal disorders are commonsymptoms of most diseases transmitted bywater-borne pathogenic bacteria.

Bacteria

Viruses are the smallest biological structures known tocontain all the genetic information necessary for their ownproduction.

Viruses are only visible with aid of electronic microscopes

Viruses are obligate parasites that require a host in whichto live

Waterborne viral infections usually involve disorders ofthe nervous system rather than of the gastrointestinaltract

Viruses

Protozoa are the lowest form of plant life

Protozoa are unicellular organisms more complex intheir functional activity than bacteria or viruses

Protozoa can be free-living or parasitic, pathogenic ornonpathogenic

Protozoal infections are usually characterized bygastrointestinal disorders of a milder form than thoseassociated with bacterial infections

Protozoa

Helminth is a term used to describe parasitic worms

The life cycles of helminths, often involve two ormore animal hosts, one of which can be human

Water contamination may result from human oranimal waste that contains helminths.

Helminths pose hazards primarily to those personswho come into direct contact with untreated water

Helminths

Analysis of water of all the known pathogens would bevery time-consuming and expensive proposition

Tests for specific pathogens are usually made onlywhen there is a reason to suspect that those particularorganisms are present

At other times, the purity of water is checked usingindicator organisms

An indicator organism is one whose presence presumesthat contamination has occurred and suggests thenature and extent of contaminant(s).

Pathogen Indicators

Faecal coliforms (FC) - is an indicator of watercontamination with faecal matter. The common leadindicator is the bacteria Escherichia coli or E. coli.

Total coliforms (TC) this encompasses faecalcoliforms as well as common soil microorganisms, andis a broad indicator of possible water contamination.

Helminth analysis investigates the presence for wormseggs in water.

Microbiological indicator tests