Remember me and also my parents in your pray friends

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SAQIB IMRAN 0341-7549889 1
Assala mu alykum My Name is saqib imran and I
am the student of b.tech (civil) in sarhad
univeristy of science and technology peshawer.
I have written this notes by different websites
and some by self and prepare it for the student
and also for engineer who work on field to get
some knowledge from it.
I hope you all students may like it.
Remember me in your pray, allah bless me and
all of you friends.
If u have any confusion in this notes contact me
on my gmail id: Saqibimran43@gmail.com
or text me on 0341-7549889.
Saqib imran.

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Environmental Engineering
Environment:
The physical and biotic habitat which surrounds us; that which can be seen,
heard, touched, smelled and tasted.
Environmental Science:
An integrative applied science that draws upon nearly all of the natural
sciences to address environmental quality and health issues.
Environmental Engineering:
Uses environmental science principles, along with engineering concepts and
techniques, to assess the impacts of social activities on the environment,
people, and to protect both human and environmental health. Environmental
engineering requires a sound foundation in the environmental sciences and
consists of;
 Provision of safe, palatable and ample water supplies
 Proper disposal of or recycling of wastewater and solid wastes
 Control of water, soil and atmospheric pollution.
Scope, Benefits and Problems in Environmental
Impact Assessment

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Benefits of Environmental Impact Assessment
The main benefits of EIA process are:
 Improved project design / siting
 More informed decision making with improved opportunities for public involvement in
decision making.
 More environmentally sensitive decisions;
 Increased accountability and transparency during the development process;
 Improved integration of projects into their environmental and social setting;
 Reduced environmental damage;
 More effective projects in terms of meeting their financial and/or socio-economic
objectives; and
 A positive contribution towards achieving sustainability.
The study of EIA effectiveness shows a number of difficulties and constraints, generally,
although not universally applicable, that continue to prevent and hinder EIA from
consistently delivering these advantages and benefits:
Scope of EIA
Small scale projects not included in most environmental impact assessment systems
although their cumulative impacts may be significant over time.
Problems in Environmental Impact Assessment
 Difficulties in ensuring adequate and useful public involvement (or participation);
 Insufficient integration of EIA work at key decision points in relation to feasibility and
similar studies in the project life-cycle; with some major decisions being made even before
EIAs are completed;
 Lack of consistency in selection of developments requiring specific environmental impact
assessment studies;
 Inadequate understanding of the relative roles of baseline description and impact
prediction;
 Poor integration of biophysical environmental impacts with social, economic and health
effects also adds to the Problems in Environmental Impact Assessment;
 Production of EIA reports which are not easily understood by decision makers and the
public because of their length and technical complexity;
 Lack of mechanisms to ensure that EIA reports are considered in decision-making;
 Weak linkages between environmental impact assessment report recommendations on
mitigation and monitoring and project implementation and operation; and
 Limited technical and managerial capacities in many countries to implement EIAs result
in Problems in carrying out Environmental Impact Assessment.

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What is Environmental Impact Assessment and
its Objectives
Definition of EIA
A systematic identification and evaluation of the potential impacts of proposed projects,
plans, programs, or legislative action relative to physical-chemical, biological, cultural and
socioeconomic components of environment is called Environmental Impact Assessment.
OR
The process of predicting, identifying, evaluating and mitigating the biological, social and
other relevant effects of developmental proposals prior to major decision being taken and
commitment made. It is an important procedure for ensuring that the likely effects of new
developmental activities on the environment are fully understood and taken into account
before the development is allowed to go ahead.
Environmental impact Assessment is an event or effect, which results from a prior event.
It can be described as the change in an environmental parameter, over a specific period and
within a defined area, resulting from a particular activity compared with the situation which
would have occurred had the activity not been initiated.

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Objectives of Environmental Impact Assessment (EIA)
 To ensure that Environmental considerations are addressed properly and incorporated into
decision making process.
 To avoid, minimize or balance the adverse significant bio-physical, social and other
relevant effects of developmental projects.
 To protect the productivity and capacity of natural system and ecological processes with
maintain their function.
 To promote development that is sustainable and optimize resources use and management
opportunities.
Characteristics of Environmental Impact Assessment
An ideal EIA should have the following characteristics:
 Apply to all activities that have significant environmental impact and address all the
impacts that are expected to be significant.
 Compare alternatives to a proposed project (including the possibility of not developing the
site), management, techniques and mitigation measures.
 Clear EIS mentioning importance of impacts and their specific characteristics to experts as
well as to non expert in the field.
 Public participation and stringent administrative review procedure
 Be on time so as to provide information for decision making and be enforceable.
 Including monitoring and feed back procedures.
Types of Activated Sludge Process - Plug Flow,
Complete Mix, SBR
Following are the types of Activated Sludge Process

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1. Plug Flow
2. Complete Mix
3. Sequencing Batch Reactor
Plug Flow (PF) Process
Involves relatively long and narrow aeration basins so that concentration of soluble
substances and colloidal and suspended solids varies along reactor length.
Complete-Mix Activated Sludge (CMAS) Process
In CMAS, mixing of tank contents is sufficient so that ideally concentrations of mixed-
liquor constituents, soluble substances (COD, BOD, NH4-N), and colloidal and suspended
solids do not vary with location in aeration basin.
Sequencing Batch Reactor (SBR) Process
 With development of program logic controllers (PLCs) and availability of level sensors
and automatically operated valves, SBR process became widely used by late 1970s.
 Sequencing Batch Reactor process is fill-and-draw type of reactor system involving single
complete-mix reactor in which all steps of ASP occur.
 Mixed liquor remains in reactor during all cycles, eliminating need for separate
sedimentation tanks.
Membrane technology has found increasing application for enhanced solids separation for
water reuse and use in suspended growth reactors for wastewater treatment. Membrane
biological reactors (MBRs) may change look of wastewater treatment in the future.
Microbial Metabolism in Biological Waste Water
Treatment

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Carbon and Energy Sources for Microbial Growth:
 Organism must have sources of energy, carbon for synthesis of new cellular
material, and inorganic elements (nutrients) such as nitrogen, phosphorus, sulfur,
potassium, calcium and magnesium;
Carbon Sources:
 Organisms that use organic carbon for formation of new biomass are called
heterotrophs; Organisms that derive cell carbon from carbon dioxide are called
autotrophs
Energy Sources:
 Energy needed for cell synthesis supplied by light or by chemical oxidation reaction;
Those organisms that are able to use light as energy source are called phototrophs;
Phototrophic organisms either heterotrophic or autotrophic;

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 Organisms that derive energy from chemical reactions are known as chemotrophs;
Chemoautotrophs obtain energy from oxidation of reduced inorganic compounds
(ammonia, nitrite, ferrous iron and sulfide); Chemoheterotrophs derive their energy
from oxidation of organic compounds
 Oxidation‐reduction reactions involve transfer of electrons from electron donor to
electron acceptor; Electron donor is oxidized and electron acceptor is reduced;
Electron acceptor available within cell during metabolism (endogenous) or it
obtained from outside cell (i.e., dissolved oxygen) (exogenous);
Respiratory Metabolism:
 Organisms that generate energy by enzyme‐mediated electron transport to external
electron acceptor
Fermentative Metabolism:
Use of internal electron acceptor and is less efficient energy yielding process than
respiration
Aerobic:
 When oxygen is used as electron acceptor the reaction is termed aerobic;
Anaerobic:
 When electron acceptors other than oxygen are involved, reaction is considered
anaerobic;
Anoxic:
 When nitrite or nitrate is used as electron acceptor, reaction is termed anoxic; Under
anoxic conditions nitrite or nitrate reduction to gaseous nitrogen occurs, also
referred to as biological denitrification.
 Organisms that can only meet their energy needs with oxygen are called obligate
aerobes
 Bacteria that can use oxygen or nitrite/nitrate as electron acceptor in absence of
oxygen are called facultative aerobes
 Organisms that generate energy by fermentation and that can exist only in
environment devoid of oxygen are obligate anaerobes
 Organisms having ability to grow in either presence or absence of oxygen are
facultative anaerobes.

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Biological De-Nitrification Process in Waste
Water Treatment System
Denitrification
 Biological reduction of nitrate to nitric oxide, nitrousoxide, and nitrogen gas
 Involves both nitrification and denitrification
 Biological nitrogen removal (BNR) is more cost effective and used more often as
compared to ammonia stripping, breakpoint chlorination and ion exchange;
 BNR is used in wastewater treatment where
o there are concerns for eutrophication;
o where groundwater must be protected against elevated NO3‐N concentration;
o where WWTP effluent is used for groundwater recharge and other reclaimed
water applications
Process Description
Two modes of nitrate removal can occur in biological processes:
1. Assimilating and
2. Dissimilating nitrate reduction
Assimilating nitrate reduction
 Involves reduction of nitrate to ammonia for use in cell synthesis;
 Occurs when NH4‐N is not available and is independent of DO concentration
Dissimilating nitrate reduction

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 Nitrate or nitrite is used as electron acceptor for oxidation of variety of organic or
inorganic electron donors
Substrate driven (preanoxic denitrification)
 Figure 7‐21 (a) most common process used for biological nitrogen removal (BNR) in
municipal WWT;
 Process consists of anoxic tank followed by aeration tank;
 Nitrate produced in aeration tank is recycled back to anoxic tank;
 Organic substrate in influent WW provides electron donor for oxidation reduction
reactions using nitrate; Process is termed substrate denitrification;
 Furthermore, process is known as preanoxic denitrification because anoxic process
precedes aeration tank
Endogenous driven (postanoxic denitrification)
 Figure 7‐21 (b), denitrification occurs after nitrification
 and electron donor source is from endogenous decay;
 Process is termed as postanoxic denitrification as BOD removal has occurred first and is
not available to drive nitrate reduction reaction
 Depends on endogenous respiration for energy
 Much slower rate of reaction than preanoxic processes
 Exogenous carbon source such as methanol or acetate is added to provide sufficient BOD
for nitrate reduction and to increase rate of denitrification
 Include suspended and attached growth systems
Biological Nitrification Process in Waste Water
Treatment System

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Definition
The removal of nitrogen by biological nitrification and denitrification is a two-step process.
In the first step (nitrification), ammonia is converted aerobically to nitrate (NO3−). In the
second step (denitrification), nitrates are converted to N2O or nitrogen gas (N2) under
anoxic conditions. Two‐step biological process in which ammonia (NH4‐N) is oxidized to
nitrite (NO2) and nitrite is oxidized to nitrate (NO3‐N).
Purpose of Nitrification
1. Effect of ammonia on receiving water with respect to DO concentrations and fish toxicity
2. Need to provide nitrogen removal to control eutrophication
3. Need to provide nitrogen control for water‐reuse applications including groundwater
recharge
4. Drinking water maximum MCL for nitrate nitrogen is 45 mg/L as nitrate or 10 mg/L as
nitrogen
5. Total concentration of organic and ammonia nitrogen in municipal wastewater in the
range 25‐ 45 mg/L as nitrogen based on flowrate of 450 L/capita.d (120 gal/capita.d)
6. With limited water supplies, total nitrogen in excess of 200 mg/L as N measured in
domestic wastewater
Nitrification Process
Nitrification process in waste water treatment is accomplished in both suspended growth
and attached growth biological processes
Suspended Growth Processes
Nitrification along with BOD removal in single‐sludge process can be achieved, consisting
of aeration tank, clarifier, and sludge recycle system
In case of toxic and inhibitory substances in wastewater, two‐sludge suspended growth
system may be considered, consisting of two aeration tanks and two clarifiers in series. The
first aeration tank/clarifier unit operated at short SRT for BOD and toxic substances
removal, followed by nitrification in second aeration tank/clarifier unit operated at long
SRT; Nitrifying bacteria grow much more slowly than heterotrophic bacteria.
Attached Growth Processes
 For nitrification, most of BOD must be removed before nitrifying organisms can be
established
 Heterotrophic bacteria higher biomass yield and dominate surface area of fixed‐film
systems over nitrifying bacteria;
 Nitrification accomplished in attached growth reactor after BOD removal or in separate
attached growth system designed for nitrification.

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 The nitrification rate for the attached-growth processes is higher than for the suspended-
growth processes. Attached-growth processes normally carry more suspended solids in the
effluent than the suspended-growth processes.
Microbiology of Nitrification
 Aerobic autotrophic bacteria are responsible for nitrification in activated sludge and
biofilm processes;
 Two‐step process in nitrication involve two groups of bacteria; First stage, ammonia is
oxidized to nitrite by one group (Nitrosomonas) and second stage, nitrite is oxidized to
nitrate by another group of autotrophic bacteria (Nitrobacter)
 Other autotrophic bacteria for oxidation of ammonia to nitrite (prefix with Nitroso‐):
Nitrosococcus, Nitrosospira, Nitrosolobus, and Nitrosorobrio
 Other autotrophic bacteria for oxidation of nitrite to nitrate (prefix with Nitro‐):
Nitrococcus, Nitrospira, Nitrospina, and Nitroeystis
Factors affecting Process of Nitrification
Environmental Factors: pH
 Nitrification process in waste water treatment is pH sensitive and rates decline significantly
at pH values below 6.8; Optimal nitrification rates occur at pH values in 7.5‐8.0 range; pH
of 7.0 to 7.2 is normally used;
 Low alkaline waters require alkalinity to be added to maintain acceptable pH values;
 Amount of alkalinity added depends on initial alkalinity concentration and amount of NH4‐
N to be oxidized;
 Alkalinity added in form of lime, soda ash, sodium bicarbonate, or magnesium hydroxide.
Environmental Factors: Toxicity
 Nitrifiers are good indicators of presence of organic toxic compounds at low
concentrations;
 Toxic compounds include: Solvent organic chemicals, amines, proteins, tannins, phenolic
compounds, alcohols, cyanates, ethers, carbamates, and benzene
Environmental Factors: Metals
 Complete inhibition of ammonia oxidation at 0.25 mg/L nickel, 0.25 mg/L chromium, and
0.10 mg/L copper
 Environmental Factors: Un‐ionized Ammonia
 Nitrification is also inhibited by un‐ionized ammonia (NH3) or free ammonia, and un‐
ionized nitrous acid (HNO2);
 Inhibition effects are dependent on total nitrogen species concentration, temperature, and
pH.

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Sources of Drinking Water
Water for drinking and domestic use may be obtained from natural sources like surface
water, groundwater and rainwater.
Surface water
Streams, rivers and lakes are the major sources of surface waters. Usually these sources
fulfill the requirements of municipal supplies. Water in these sources originates partly
from groundwater outflows and partly from rainwater which flows over the terrestrial
areas into the surface water bodies. Outflows from groundwater brings in, the dissolved
solids.
The surface run off contributes turbidity, organic matter and pathogenic organisms.
Usually in surface water bodies, the dissolved mineral particles will remain unchanged
while the organic impurities are degraded by chemical and microbial action. In slow-
flowing or impounded surface waters sedimentation of suspended solids occurs naturally.
Due to the lack of nutrients micro-organisms wil1 die off.
Although clear water from rivers and lakes requires no treatment, on taking into account
the risk of incidental contamination, it is better to practice chlorination. Unpolluted surface
water of low turbidity may be purified by slow sand filtration alone. Alternatively, rapid
sand filtration followed by chlorination can be practiced.

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Groundwater
Wells and springs constitute groundwater supplies. Groundwater mostly originates from
infiltrated rainwater which after reaching the aquifer flows through the underground.
Groundwater provides water to meet the requirements of individual household supplies as
well as municipal supplies.
The treatment processes also differ in these two cases with simply boiling the water before
use for household supplies. However, municipal supplies require one or more treatment
processes depending upon the impurities found in the water. A little contamination of
groundwater occurs from organic and inorganic soil particles, animal and plant debris,
fertilizers, pesticides, microorganisms, etc. as it flows through the soil layers. In spite of
this contamination, infiltration causes partial removal of suspended particles including
microorganisms. Organic substances are also degraded by oxidation. Partial removal of
microorganisms occurs by the death of cells due to lack of nutrients.
Thus, properly withdrawn groundwater will be free from turbidity and pathogenic
microorganisms. It is important to select the location of groundwater supply at a safe
distance from other sources of contamination.. If done so, groundwater will be of high
quality and can be used directly without any treatment.
Rainwater
Rainwater runoff from roofs can be collected and stored for domestic use. Rainwater will
be of high quality and the only possible source of contamination is airborne
microorganisms that too will be present in very low numbers.
Upland Lakes and Reservoirs
Typically located in the headwaters of river systems, upland reservoirs are usually sited
above any human habitation and may be surrounded by a protective zone to restrict the
opportunities for contamination. Bacteria and pathogen levels are usually low, but some
bacteria, protozoa or algae will be present. Where uplands are forested or peaty, humic acid
can color the water.
Many upland sources have low PH which requires adjustment.
Rivers, Canals and Low Land Reservoirs
Low land surface waters will have a significant bacterial load and may also contain algae,
suspended solids and a variety of dissolved constituents.

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Atmospheric Water Generation
It is a new technology that can provide high quality drinking water by extracting water
from the air by cooling the air and thus condensing water vapor
What is Disinfection and Methods of Disinfection
of Water
Definition of Disinfection
Disinfection is a process to destroy the disease causing organisms or
pathogens.
Methods of Disinfection of water
Disinfection of water can be done by

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1. Boiling the water
2. Physical method (Ultraviolet radiation)
3. A chemical inactivation of pathogen
In the water treatment processes, pathogens & other organisms can be partly physically
eliminated through coagulation, flocculation, sedimentation, & filtration, in addition to the
natural die-off. After filtration, to ensure pathogen free water, the chemical addition of
chlorine (so called chlorination), rightly or wrongly, is most widely used for disinfection of
drinking water. This less expensive & powerful disinfection of drinking water provides
more benefits than its short coming due to disinfection by-product (DBPs). DBPs have
to be controlled. The use of ozone & ultraviolet for disinfection of water & waste water is
increasing in the United States.
Chemical Characteristics of Sewage - BOD, COD,
Nutrients, DO
Sewerage characteristics can be divided into three broad categories:
 Physical (Temperature, colour, smell, solids)
 Chemical (BOD, COD, Nutrients and dissolved solids; and

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 Biological
Chemical Characteristics of Sewage (Waste Water)
 In sanitary sewage about 75 % of suspended solids and 40% of filterable solids are organic.
 These solids are derived from both animals, plant and humans. Organic compounds usually
consist of C; H; O; N along with S; P and Iron.
 The organic substances found in sewage are Protein (40-60%); Carbohydrates (25-50%),
fats and oils (10%).
 Along with these organic compounds small amount of synthetic organic compounds like
VOCs, pesticides, insecticides, Organic Priority Pollutants are also presents in sewage.
 Sewage also contain inorganic substances.
 Tests like BOD, COD, Nitrogen, phosphorus, alkalinity etc. give the chemical
characteristics of sewage.
BOD (Biochemical Oxygen Demand):
When biodegradable organic matter is released into a water body, microorganisms feed on
the wastes, breaking them into simpler organic and inorganic substances. When this
decomposition occurs in aerobic environment the process produces non-objectionable,
stable end products like CO2, SO4, PO4 and NO3. A simplified form of Aerobic
decomposition is
O.M + O2 + Microorganisms
CO2 + H2O + C5 H7 NO2 (New Cells) = stable Products like NO3; PO4; NO3)
When sufficient O2 is not available Anaerobic decomposition occurs by different
microorganisms. They produce end products that can be highly objectionable, including
H2S; NH3 and CH4.
The reaction is O.M + Microorganisms
CO2 + H2O + C5 H7 NO2 (New Cells) = Unstable Products (NH3; H2S; CH4
 Such products are usually unstable.
 Bacteria placed in contact with organic matter will utilize it as food source.
 In the utilization of the organic material it will eventually be oxidized to stable end products
such as CO2 and H2O etc.
 The amount of oxygen required by the bacteria to oxidize the organic matter present in
sewage to stable end products is known as biochemical oxygen demand.
 BODu is the maximum amount of oxygen usage by microorganisms over a long period of
time. A good measure of maximum bioavailability.
 BOD5 is the amount of oxygen consumed (in mg/L) over a 5-day period at 20 o
C (in the
dark). BOD5 is a measure of the bioavailability over a 5-day period under controlled
conditions.

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CBOD
Carbonaceous biochemical oxygen demand or CBOD is a method defined test measured
by the depletion of dissolved oxygen by biological organisms in a body of water in which
the contribution from nitrogenous bacteria has been suppressed. CBOD is a method defined
parameter is widely used as an indication of the pollutant removal from wastewater. It is
listed as a conventional pollutant in the U.S. Clean Water Act.
Chemical Oxygen Demand
 In addition to CBOD and NBOD measured, there are two other indicators to describe the
oxygen demands of wastewater. They are Chemical oxygen demand and theoretical oxygen
demand.
 The biodegradable organic matters are degraded completely by microorganisms either by
CBOD or NBOD.
 There are some organic matters like cellulose, phenols, benzene and tannic acid which are
resistant to biodegradation. Similarly, other organic matters like pesticides, insecticides
and various industrial chemicals are non biodegradable and they are toxic to
microorganisms.
 The COD is a measured quantity that does not depend on microorganisms. To calculate the
concentration of oxygen for non biodegradable materials a strong oxidizing agent known
as potassium dichromate will be used.
 The reaction is Organic matter (CaHbOc) + Cr2O7
-2
+ H2O – Cr +3
+ CO2 + H2O
 The COD test is much quicker than BOD test, but it does not distinguish between the
biodegradable and non biodegradable organic matter. The measured COD is usually more
than BOD if there is non biodegradable impurity present. If all are the biodegradable
organic matter, then COD remains the same as that of BOD. Roughly the BOD/COD is 0.4
to 0.8.
Theoretical Oxygen Demand (TheoD):
Organic matter of animal or vegetable origin in wastewater is generally a combination of
carbon, hydrogen, oxygen, nitrogen and other elements. If the chemical composition of an
organic matter is known then the amount of oxygen required to oxidize it to carbon dioxide
and water can be calculated using stoichiometry. This amount of oxygen is known as
Theoretical Oxygen Demand. If that oxidation is carried out by bacteria then it is BOD, if
by chemical process then it is COD. If a combination of both then it is TheoD.
Physical Characteristics of Sewage

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Sewage Characteristics
Sewerage characteristics can be divided into three broad categories:
1. Physical (Temperature, colour, smell, solids)
2. Chemical (BOD, COD, Nutrients and dissolved solids; and
3. Biological
Physical Characteristics of Sewage
Following are the detailed physical characteristics of Sewage:
Temperature:
 The normal temperature of sewage is commonly higher than water supply due to domestic
and industrial activities. Depending on geographical location, the mean annual temperature
of sewage is in the range of 10 to 21°C. Temperature of sewage is an important parameter
because of its effect on chemical reaction rates and aquatic life.
 Increase temperature can cause a change in fish species that are present in water bodies.

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 Similarly, oxygen is less soluble in warm water, while some species of aquatic life
population increases with temperature causing more demand of oxygen and result in
depletion of dissolved oxygen in summer.
 Similarly, sudden change of temperature cause mortality of species.
Colour:
 Fresh sewage is light brownish grey colour.
 At a temperature of above 20 °C, sewage will change from fresh to old in 2 - 6 hours.
 The old sewage is converted to dark grey and black color due to anaerobic activities, known
as stale or septic color.
 Some industrial sewage also add color to domestic wastewater.
 The grey, dark grey and black color is due to formation of sulfide produced under anaerobic
conditions reacts with the metals present in wastewater.
Odor:
 Fresh domestic sewage has a slightly soapy or oil odour.
 Stale sewage has a pronounced odour of Hydrogen Sulphide (H2S).
 The odor at low concentration has no effect, but high concentration causes poor appetite
for food, lower water consumption, impaired respiration, vomiting etc.
Solids:
 Solids comprise matter suspended or dissolved in water and wastewater.
 Solids are divided into several different fractions and their concentration provide useful
information for characterization of wastewater and control of treatment processes.
Total solids:
 Total solids (TS) are the sum of total suspended solids and total dissolved solids (TDS).
Each of these groups can further be divided into volatile and fixed fractions.
 Total solids (TS) is the material left in the evaporation dish after it has dried at 103-105
°C.
 Total solids can be expressed in mg/L.
Total suspended solids:
 Total suspended solids (TSS) are referred to as non-filterable residue.
 It is determined by filtering a well mixed sample through 0.45μm to 2 μm pore sized
membrane. The residue retained on the filter is dried in an oven at a temperature of 103-
105 °C for at least 1 hour.
 TSS is expressed in the unit mg/L.
Fixed and Volatile Solids:

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 The residue for total solids, total suspended solids or total dissolved solids tests is ignited
to constant weight at 500 o
C ± 50.
 The weight lost on ignition is called volatile solids, whereas the remaining solids represent
the fixed total suspended or dissolved solids.
 The determination of volatile portion of solids is useful in controlling waster water
treatment plant operations because it gives a rough estimation of the amount of organic
matter present in the solid fraction of waster water, activated sludge and industrial waste.
Absorption
 Measure of amount of light, of specified wavelength, absorbed by constituents in
solution;
 Absorbance measured with spectrophotometer using specified wavelength (254 nm)
 Absorbance, measured using spectrophotometer and fixed path length (usually 1 cm) is
given by:
Absorbance
where A = absorbance, absorbance units (au)/cm
Io = initial detector reading for blank (distilled water) after passing through solution of
known depth I = final detector reading after passing through solution containing
constituents of interest
Turbidity
 Measure of light‐transmitting properties of water, used to indicate quality of waste
discharges and natural waters with respect to colloidal and residential suspended matter
 Measurement based on comparison of intensity of light scattered by a sample to the light
scattered by reference suspension under same conditions. Formazin suspensions are used
as primary reference standard
 Results of turbidity reported as nephelometric turbidity units (NTU)
 Relationship between turbidity and TSS for settled and filtered secondary effluent from
activated sludge process:
Relationship between turbidity and TSS for settled and filtered secondary effluent from
activated sludge process

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 TSSf vary for each treatment plant; TSSf for settled secondary effluent and for secondary
effluent filtered with granular medium depth filter vary from 2.3 to 2.4 and 1.3 to 1.6,
respectively
Conductivity
 Electrical conductivity (EC) is measure of ability of solution to conduct electrical current
 Electrical current is transported by ions in solution, conductivity increases as concentration
of ions increases;
 EC value is used to substitute measure of TDS concentration; EC of water important
parameter to determine its suitability for irrigation;
 Salinity of treated wastewater to be used for irrigation is estimated by its EC;
 SI units: millisiemens per meter (mS/m);
 Estimation of TDS of water sample based on measured EC value:
TDS (mg / L) ≅ EC (dS / m)×(0.55 − 0.70)
Density and Specific Gravity
Physical Characteristics of Sewage also include aspects like density and specific gravity
of the sewage.
Density: Mass per unit volume expressed as g/L or kg/m3; density of domestic
wastewater is the same as that of water at same temperature;
Specific Gravity: sw =ρw/ρo
where ρw = density of wastewater
ρo = density of water
Both density and specific gravity are temperature dependent and will vary with
concentration of TSS in wastewater.
Types of Grit Chambers in Waste Water
Treatment
The objectives of Grit Chambers are:
1. Protect moving mechanical equipment from abrasion and abnormal wear
2. Reduce formation of heavy deposits in pipelines, channels and conduits
3. Reduce the frequency of digester cleaning caused by excessive accumulation of grit
Types of Grit Chamber
1. Horizontal flow (Rectangular or square) (configuration type)

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Designing a Rectangular horizontal flow type grit chamber:
 Cross-sectional area, Ax = (Qdesign / Vh) for each unit (Vh ≈ 1 ft/sec), depth ≈ 3-5 ft
 Assuming (tD = 1-2 minutes), determine the length L = Vh * tD (Add 10% additional)
 Check the SLR (1200-1700 m3
/m2
-day) and Vs (≥ 0.01 m/sec). Grit produced is about 1.5
ft3
/ML of wastewater flow. Add to depth {1ft FB + grit}
2. Aerated Grit Chamber
Basic Info
 Air is introduced along one side of a rectangular tank to create a spiral flow pattern
perpendicular to the flow through the tank.
 If the velocity is too great, grit will be carried out of the chamber; if it is too small,
organic material will be removed with the grit.
 Normally designed to remove 0.21-mm-diameter or larger, with 2-5-minute
detention periods at the peak hourly rate of flow
 Air diffusers are located about 0.45 to 0.6m above the normal plane of the bottom.

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Aerated Grit Chamber
Designing an Aerated grit chamber:
 Assume a “tD” (3-4 min), determine the volume of the basin.
 Assume a depth (D = 08-15 ft), determine the surface area of the basin. And check the
SLR (1200-1700 m3
/m2
-day)
 The amount of grit produced is about 1.5 ft3
/ML of wastewater flow. Add suitable depth
from grit and free board.
 Calculate the amount of air required (0.2-0.5 m3
/min/m length of the tank)
Advantages & Disadvantages of Comminutors
Advantages
 Elimination of extra steps and problems involved in the excavation of the disposals of
screening (screened material)
 Often difficult to dispose highly polluted screenings - In USA if buried, 6 inches of cover
material should be used
 Highly suitable for small treatment plants. e.g. : mountain or beach resorts.
Disadvantages
 Frequent maintenance of cutting tools ( delicate equipment)
 Risk accumulation of comminuted materials (textiles, vegetable fibers) eventual clogging
of pumps and piping.
 These materials to form floating scum in anaerobic digestion
 Problems in trickling filter (clogging of distribution pipe holes) mainly used in activated
sludge process.

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Definitions in Waste Water Treatment
Sludge Volume Index (SVI-TEST)
It is the measure of the settleability and compatibility of sludge and is made from a
laboratory column setting test.
Definition
The sludge volume index is defined as ‘the volume in mm occupied by 1 gm of sludge
after it has settled for a specified period of time’ generally ranging from 20 min to 1 or 2
hr in a 1 – or 2-l cylinder. One-half hour is most common setting time allowed to the
mixed liquor to settle for 30 min. ( larger cylinder is desirable to minimize bridging of
sludge floe and war effects). Take the reading let Vs is the settled volume of sludge (ml/l)
in 30 min.
* If SVI is 50 - 150 ml/mg, the sludge settle ability is Good.
Return Activated Sludge System:
1. The activated sludge form the underflow of the final setting tanks should be returned to the
inlet of the aeration tanks at a rote sufficient to maintain the MLSS concentration at the
design value.
2. The flow are needed for return-sludge is determined form the incoming sewage flow rate
and the concentration at which the sludge is with drawn form the final setting tanks.
Hence a simple measure of the underflow concentration form the setting tanks is required.
The parameter conventionally employed for this purpose the sludge volume index, SVI
which is defined as 4 the volume occupied by sludge containing 1.0g of sludge soiled (dry
weight) after 30 min setting and thus it has ht units ml/g. Some time represented as SDI
i.e sludge density index. Once the SVI and operating MLSS concentration (x) is known,
the required rate of activated sludge return can be determined
R = 100 / [ 106/ (x) (SVI) -1] where r = return sludge flow rate as a % age of incoming
sewage flow.
SEDIMENTATION:
It is the removal of solid particles form a suspension by settling under gravity.
CLARIFICATION:
It is a similar term which refers specifically to the function of a sedimentation removal.

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THICKENING:
It means the separation of water from Suspended Solids where R = return sludge flow
rate (ML/D) for Q in ML/D)
SURFACE GEOMETRY OF FINAL SEDIMENTATION TANKS:
VARIATION OF THE ACTIVATED SLUDGE PROCESS:
1. Activated sludge was introduced in 1941 and has undergone many variations and
adaptations.
2. The main objective of many modifications has been to increase the loading capacity of the
basic plug flow activated sludge plant by provision of optimum condition design
parameters for different variations are summarized in table. It is worthy of note that 5
modifications tapered aeration step aeration the CMAS process, the pure oxygen system
and the deep shaft process all aim at either the improvement of oxygen transfer efficiency
t the efficient distribution of available oxygen to match demand. A flow sheet of most of
the commonly used variations is similar to that of CAS (Conventional Activated Sludge).
CONVENTIONAL ACTIVATED SLUDGE:
Volumetric loading = kg of BOD
m3
-d
Aerial loading rate = gm of BOD
m3
-d
Td = V/Q in days and grater than 5 days.
ALGAL-BACTERIAL SYMBOPSTS:
The combined and mutually- been facial action of algae and bacteria in this process is
called algal-bacterial symbioses.
 Shock loading (CSTR)
 BODu
Aerated Lagoons:
Aerate lagoons are activated sludge units operated without sludge return. Historically they
were developed from waste stabilization ponds in temperate climate where mechanical
aeration was used to supplement the algal oxygen supply in winter. It was found, however
that soon after the aerations were put into operation the algal disappeared and the microbial
flora resembled that of activated sludge. Aerated lagoons were now usually design as
completely mixed not-return activated sludge units. Floating aerates are most commonly
used to supply the necessary oxygen and mixing power.

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Sludge Treatment:
Anaerobic sludge treatment cell Primary Sedimentation Tank and Secondary
Sedimentation Tank are basically organic these can treated to aerobic.
 Anaerobic ponds and septic tank are for waste water treatment .
 Sludge treatment = Anaerobic sludge treatment.
COLD DIGESTION:
 Two stage digestion up
 High rate digestion up
 Fixed film processes. A swm zone
SLUDGE DIGESTION:
SLUDGE: the concentrated impurities settled at the bottom of the flower bed of
sedimentation tanks.
Digestion:
To decompose or breakdown by heat and moisture or chemical action. (to invent food
equable forms)
Sludge treatment:
Aerobic digestion it is defined as ‘it is the use of microbial organisms in the absence of
oxygen I for the stabilization of oxygen materials by conversion to mean and inure produce
including CO2.
Organic matter + H2O (amoebas) CH4+ CO2 + NH3+ H2S + heat
Benefices of anaerobic digestion. Types of anabolic detectors. It’s of two types:
 Conventional (stranded) or low-rate digester or cold digester.
 High rate digesters / two stage digester are characterized by continuous miring except at
time of sludge with draw.
What is the Composition of Wastewater?

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Constituents of Waste Water
Constituents of Waste Water are characterized in terms of its physical, chemical and
biological composition
Physical Characteristics
Solids content
 Floating matter
 Settleable matter
 Colloidal matter
 Matter in solution
Particle size distribution; Turbidity; Color; Transmittance; Temperature; Conductivity;
Density; Specific gravity; Specific Weight
Solids classification
Solids interrelationships
Settleable solids: Placing 1‐L sample in Imhoff cone and noting volume of solids in mm
that settle after 1 h; Typically 60% of suspended solids (SS) in municipal wastewater are
settleable
Total solids (TS): Obtained by evaporating wastewater sample to dryness (at 103‐ 105°C)
and measuring mass of residue
Total suspended solids (TSS): Filtration step is used to separate TSS from total dissolved
solids (TDS); Portion of TS retained on filter (e.g., Whatman fiber glass filter‐GF/C)
measured after being dried at 105°C
Total Suspended Solids (TSS)
More TSS measured as pore size of filter used is reduced;
Important to note filter paper pore size, when comparing TSS values;
TSS and BOD universal effluent standards by which performance of treatment plants is
judged for regulatory control purposes
Total Dissolved Solids (TDS)

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Solids contained in filtrate that passes through a filter with nominal pore size of 2 μm or
less are classified as dissolved; Size of colloidal particles in wastewater typically in range
from 0.01‐1 μm
Volatile and Fixed Solids (VS and FS) Material volatilized and burned off when ignited
at 500 ± 50oC classified as volatile solids (VS);
In general, VS are organic matter
Residue that remains after sample is ignited at 500 ± 50oC classified as fixed solids (FS);
TS, TSS, and TDS comprised of both VS and FS Ratio of VS to FS used to characterize
wastewater with respect to amount of organic matter present
Particle Size Distribution (PSD)
To understand nature of particles that comprise TSS in wastewater, measurement of
particle size is undertaken
PSD important in assessing effectiveness of treatment processes (secondary sedimentation,
effluent filtration, and effluent disinfection)
PSD methods can be divided into two general categories:
1. Methods based on observation and measurement
2. Methods based on separation and analysis techniques
Commonly used methods for particle size analysis:
1. Serial filtration: Wastewater sample is passed sequentially through series of membrane
filters with circular openings of known diameter, and amount of suspended solids retained
in each filter is measured.
Electronic Particle Counting
 Particles in wastewater are counted by diluting a sample and then passing diluted sample
through calibrated orifice or past laser beams;
 As particles pass through orifice, conductivity of fluid changes, owing to presence of
particle. Change in conductivity is correlated to size of equivalent sphere;
 Similarly, as particle passes by laser beam, it reduces intensity of laser because of light
scattering. Reduced intensity is correlated to diameter of particle. Particles counted are
grouped into particle size ranges. In turn, volume fraction corresponding to each particle
size range is computed.

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Microscopic Observation:
Placing small wastewater sample in particle counting chamber and counting individual
particles;
 To aid in differentiating different types of particles, various types of stains are used;
 In general, microscopic particle counting is impractical on routine basis;
 However, it can be used to qualitatively assess nature and size of particles in wastewater
The typical composition of wastewater based on strength. The important characteristics
measured in wastewater included...
 Biochemical Oxygen Demand (BOD) [100-300 mg/L as O2]
 Suspended solids (SS) [100 – 350 mg/L]
 Settleable solids [5-20 mL/L]
 Total Kjeldahl nitrogen (TKN) [20-80 mg/L]
 Total Phosphorus [5-20 mg/L as P]
A typical solids analysis of wastewater, of the total solids, 50% is dissolved, 50%
suspended. Of the suspended solids, 50% will settle. Industrial activity changes the
composition of wastewater, often introducing toxic substances such as chromium and
cadmium from plating operations.
Food to Microorganisms Ratio (F/M)
Definition
A parameter of organic loading rate in the design aerated sludge parameter in the design of
Trickling Filter in organic loading rate = kg of BOD / m3-d
F/M ratio =
F/M ratio = BOD / MLSS x t kg of BOD / Kg of MLSS/day
FM ratio varies between 0.2 -0.5 day-1
 F/M ratio -0.5 day-1 has a good settleabilty of a sludge. ( even in some cases it can go to
1)
 F/M ratio -<0.2 Food is very limited so the bacteria will die.
 F/M ratio 70.5 day-1
Food is more so the bacteria will move the effluent (failure of the
system)
 If high F/M ratio, filamentous bacteria will also grow. They not settle easily because of
long tails, get entangled with each other. Food to micro organism ratio(F/M) is a common

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used parameter in the activated-sludge process which is defined as the kg of BOD5applied
per kg MLSS per day.
Derivation of F/M Ratio:
Q = Flow of Sewage (m3/day)
BOD = organic matter (mg/l)
FOOD = Q (m3/day) x BOD (mg/l)
FOOD = Q x BOD / 1000 (Kg of BOD/ day)
V = Volume of Aeration (m3)
MLSS = Mixed liquor suspended solids (mg/l)
Micro-organisms = V (m3) x MLSS (log/l) / 1000 = V x MLSS / 1000 (kg of MLSS in
aeration tank)
Uses & Design of Flow Equalization Tank
Definition:
Flow equalization is method used to overcome the operational problems and flow rate
variations to improve the performance of downstream processes and to reduce the size &
cost of downstream treatment facilities. To prevent flow rate, temperature, and
contaminant concentrations from varying widely, flow equalization is often used.

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Objective
Give a relatively constant flowrate to the downstream operations and processes
Functions of FET
 Dampen the daily variation in flowrate and loadings
 Reduce the required size of the downstream treatment facilities
 Feasible dry weather flows in separate sewer system and sometimes for storm
Effects of flow equalization
 10-20% of BOD entering is stabilized in the equalization basin
 23-47% of SS is further removed in the primary clarifier
 reduce shock load on biological process
Why to Use flow Equalization Tanks
Variations occur characteristically in domestic wastewater flow rate and composition as a
result of cyclic activities of the human population. Additional variations are commonly
imposed by a combination of:
1. Random and cyclic activities in the collective industrial-wastewater-generating segment of
the community and
2. By storm-related effects of infiltration and inflow
3. In addition, the average waste water flow rate at typical municipal treatment plants may be
expected to increase by 25 to 100 percent or more over the design life of the facilities.
4. Operation of waste water treatment plant at uniform conditions is assumed to be
advantageous. It results in improved efficiency, reliability, and control of various physical,
chemical and biological treatment processes. Costs can also be reduced by elimination of
excessive peak treatment capacity and from reduced periods of operation under peaking
conditions.

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Design of Flow Equalization Tanks
The design of equalization facilities requires evaluation and selection of a number of
features:
1. Type and magnitude of input variations
2. Required volume
3. Facility configuration
4. Pumping/control mode
5. Type of construction
6. Appurtenances; aeration, mixing, odor control, cover, flushing
7. Cost and benefits
Benefits - Advantages of Flow Equalization Tank
1. Reduction of peaking requirements
2. Reduction of process overloads at existing plants under some conditions
3. Protection against toxic upsets
4. Potential reduction of operational problems
5. Provides increasing benefits with increasing plant complexity
6. Placement of equalization following primary treatment minimizes operation and
maintenance, and minimizes requirements for solids removal, aeration, and odor control
equipment.
To Measure COD of WasteWater using Open
Reflux Method
History of COD :
KMnO4 was used as oxidizing agent for many time pb with KMnO4 was that different value
of COD obtained due to strength change of KMnO4. BOD value obtained greater than COD
with KMnO4 means KMnO4 was not oxidizing all the substances. Tthen ceric sulphate
potassium loadate and potassium dichromate all tested separately and at the end potassium
sichromate was found practical.
Pottassium dichromate is used in excess a mount to oxidize all the organic matter, this
excess aomunt can be found at the end by using ferrousiion.
Method for cod test :
1. open reflux (drawback: end product is dangerous and cannot be discharged in open
draws)

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2. close reflux (same chemicals as for open reflux but sample and chemicals used in less
quantity) spectro photometric (septrophotometer) titremetric ( titration)
Chemicals/ regents in open reflux method:
1. Potassium di-chromate (oxidation agents)
2. Sulphuric acid.
3. Mercuri sulphate (Hgs04)
4. Ferrous ammonium sulphate (Fe NH4)2 (So4)2 0.25 N used as tritrante,
5. Fezroin indicator.
Limitations of COD:
 cannot differentiate between biodegradable and non-biodegradable material
 N-value cannot be accurately found.
Advantages of COD:
1. can be performed in short time i.e 30 min can be correlated with BOD with a factor.
2. More biological resistant matter, more will be the difference in Bod and Cod results,
Apparatus
1. Digestion vessels (vial)
2. COD Reactor
3. Spectro-photometer
4. Premixed Reagents in Digestion Vessel (vials)
5. K2G2O7
6. Concentrated H2SO4
7. HgSO4
8. Ag2SO4
Procedure:
1. Place Approximately 500ml Of Sample In a clean blender bowl and homogenize
at high speed for two minutes. blending the sample ensures a uniform distribution
of suspended solids and thus improves the accuracy of test results.
2. Pre heat the COD reaction to Iso c
3. Carefully remove the cap of COD digestion Reagent vial.
4. While holding The vial at a 45 degree angle carefully pipette 2 ml sample into the
vial.
5. Replace and tighten the cap.
6. Holding the vial by the cap in an empty sink, gently invert several times to mix the
contents they will become very hot during mixing.
7. Place the vial in preheated COD reaction.

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8. Prepare a reagent blank by repeating step 3 through 6, substituting2 ml of distilled
water in place of sample.
9. Incubate the vial for two hours at size.
10.Turn off the reaction off and allow the vials to cool to 120 degree and less. invert
each vial several times while still warm place vial in a cooling reach and allow
them to room temp.
11.Measure the COD using spetrcophotometer method.
Public Health Engineering
The public health engineering sector is responsible for the Collection of water, purification,
transmission and distribution of water. A Public Health Engineer has to perform his job by
calculating design flow, design population, design area and population density
1. Collection of water
2. Purification works
3. Transmission works
4. Distribution works
Water Works Explained
1. Collection of water:
This includes the collection of water from all available sources to ensure continuous
supply of water to the community.
2. Purification works:
Quality of the collected water is checked by physical and chemical tests on water and if
the quantity is not satisfactory and according to WHO standards then, purification or
treatment of water is done to make it suitable for its intended use e.g. cooking, drinking,
bathing, washing etc.
3. Transmission works:
Transmission works includes measure taken to ensure the purified supply of water by
laying out conduits, which do not affect the quality of water
4. Distribution works:
Water is then distributed to the consumers in desired quantity at adequate pressure. The
quantity of water may be different for residential, commercial and industrial zones. So
accordingly, there should be a difference between the quantities of water that they will
receive and hence the transmission works.Similarly, the pressure of water is also
important in industries, storied buildings, and hilly areas.
Design population:
It is the no. of people for whom the project is designed. The population should be
considered as it would be at the end of design period.
Design Flows:

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The maximum discharge required at the end of transmission system is called design flow.
Per capita consumption is the average intake of water per person. It may be for a single
day, a week, a month or annually. It can be found out by dividing the total consumption of
water by the number of individuals in population using that water. The flow of water for
design is calculated by multiplying the average per capita consumption annually with the
design period (in years) and the design population.
Design period:
It is the number of years in future for which the excess capacity is provided. For this amount
of time the proposed system, its component structures and equipment should be appropriate
and adequate. The design period depends upon:
 Life of components system structures used.
 Ease of expansion of the project
 The type of technology used
 The rate of increase of population
 The rate of increase in water demand.
The flow required for design period must be estimated and not over-estimated, to prevent
the project from becoming un-economical and over-burdening the community with extra
cost.
Population density
The number of persons per unit area – e.g. persons/Km2
Population Forecasting Methods & Techniques
Population is one of the most important factors for design of the water systems, so it should
be estimated, so as to know the increasing demand and ensure continuous supply to them.
Population data is obtained by previous records and the rate of increase is found out and
this used for further analysis, which may be by using the methods described below
1. Arithmetic growth method
2. Geometric growth method
3. Curvilinear method
4. Logistic method
5. Decline growth method
6. Ratio growth

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Arithmetic growth method:
It is based on the assumption that the rate of growth of population is constant. It means that
the each year population increase by the same increment.
Mathematically;
dp / dt = Ka
Where,
dp / dt is the rate of change of population
Ka = the constant arithmetic increment
Ka can be determined by finding the slop of the graph of population against time. The
population in the future is thus estimated.
Geometric method:
It is based on the hypothesis that rate of change of population is proportional to the
population. According to this, method it is assumed that the rate of increase of population
growth in a community is proportional to the present population.
Mathematically:
dP /dt ∝ P => dp / dt = Kg where Kg = Geometric Growth constant.
If P0 is the population at any time t0 and Pf is the population at time tf then
∫Pf P0 dp/p = Kg ∫ tf t0 dt = Ln (Pf/P0 = Kg (tf/t0)
=> Ln (Pf/P0 = Kg Δt
=> (Pf/P0 = (e) Kg Δt and Pf = P0 (e) Kg Δt
This method gives somewhat larger value as compared to arithmetic method and can be
used for new cities with rapid growth. In normal practice, arithmetic and geometric growth
average is taken.

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Curvilinear method:
In this it is assumed that the population of a city will grow, in the same manner as in other
cities in the past. This similarity between the cities includes geographical proximity,
similarity of economic base, access to similar transportation system etc. In practice it is
difficult to find similar cities.
Logistic method:
When the growth rate of population due to birth, death and migration are under normal
situation and not subjected to extraordinary changes due to unusual situation like war,
epidemics earth quakes and refugees etc. Then this method is used:
According to this method
P = P sat / (1+ ea
+ bΔt), where P sat is the saturation population, of the community and a, b are
constants. P sat, a and b can be determined from three successive census populations and
the equations are
Psat = 2 P0 P1P2 - P1
2
(P0 + P2) / (P0 P2 - P1
2
)
Decline growth method:
This method like, logistic, assumes that the city has some limiting saturation population
and that its rate of growth is a function of population deficit;
Ratio method:
Ratio method of fore casting is based on the assumption that the population of a certain
area or a city will increase in the same manner to a larger entity like a province, or a country.
It requires calculation of ratio of locals to required population in a series of census years.
Projection of the trend line using any of the technique and application of projected ratio to
the estimated required population of projected ratio to the estimated required population in
the year of interest. This method of forecasting does not take into account some special
calculations in certain area but have the following advantages.
Estimation of Water Demand
While estimating the water demand, the above factors should be considered e.g. the size of
the city; its population does matter when estimating the water demand. The more the size
of population, more will be the demand. Estimation of water demand is necessary to:
 Calculate design flow

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 Determine the pumping power of machines to be used
 Reservoir capacity
 Pipe capacity
To estimate water demand, following parameters must be determined or calculated.
To determine the maximum water demand during a fire, the required fir flow must be added
to the maximum daily consumption rate. The shortage is fulfilled by elevated storage tanks
which have been filled during lower demand in usual days
Keywords: county population forecasts, population forecasting, forecasting population
growth, population forecasting methods, growth forecasting, demographic forecasting, fire
water demand, fire flow demand, firefighter demand,
1. Average daily water consumption: It is based on complete one year supply of water. It
is the total consumption during one year, divided by the population.
q = (Q / P x 365) lpcd (liters per capita per day)
2. Maximum daily consumption: It is the maximum amount of water used during one day
in the year. This amount is 180% of the average daily consumption
MDC = 1.8 x Avg. daily consumption. It is usually a working day (Monday) of summer
season.
3. Maximum weekly demand: The amount of water used by a population during a whole
single week in a study span of 1 year.
Maximum weekly demand = 1.48 x Avg. D. C
Maximum monthly demand = 1.28 x Avg. D. C
Maximum hourly demand = 1.5 x Avg. D. C
Maximum daily demand = 1.8 x Avg. D. C
4. Fire water demand | Fire Demand: The amount of water used for fire fighting is termed
as fire demand. Although, the amount of water used in fire fighting is a negligible part of
the combine uses of water but the rate of flow and the volume required may be so high
during fire that it is a deciding factor for pumps, reservoirs and distribution mains.
Minimum fire flow should be 500 gpm (1890 L/m)
Minimum fire flow should be 8000 gpm (32, 400 L/m)
Additional flow may be required to protect adjacent buildings.
Sectoral Consumption of Water
1. Domestic use
2. Commercial use
3. Public use
4. Loss and waste

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Domestic use of water:
Domestic uses of water include the consumption of water for drinking, washing, cooking,
toilets, livestock etc. the domestic average use per capita per day is 50 – 90 gallons (70 –
380 liters per capita per day). This use is increasing by 0.5% - 1.0% per year and at this
time comprises 50% of all the uses of water. Water uses are for drinking, cooking, meeting
of sanitary needs in houses and hotels, irrigating lawns etc. Residential water use rates
fluctuate regularly. Average daily winter consumption is less than annual daily average,
whereas summer consumption averages are greater. Similarly, peak hourly demand, is
higher than maximum. No universally applied rule for prediction
Commercial and industrial:
This is the amount of water used by the shops, markets, industries, factories etc. It
contributes 15 – 24% of total use of water. It includes factories, offices and commercial
places demand. It is based on either having a separate or combined water supply
system. Demand of water based on unit production: No. of persons working and floor area
Public use:
The public use of water is that one which is used by city halls, jails, hospitals, offices,
schools etc. This consumes 9% of total use of water. Its water demand is 50 – 75 liters per
capita per day. Fire protection's need of water is also fulfilled by this sector. The fire
demand does not greatly affect the average consumption but has a considerable effect on
peak rates. Schools, hospitals, fire fighting etc
Loss and wastes:
: Unauthorized, connections; leakage in distribution system, Hydrant flushing, major line
breakage and cleaning of streets, irrigating parks. Total consumption is sum of the above
demands. The water which is not intended for specific purpose or use is also called "Un-
accounted for". Loss and wastage of water is due to:
1. Errors in measurements
2. Leakages, evaporation or overflow
3. Un-metered uses e.g. fire fighting, main flushing
4. Un-authorized connections
Factors affecting the use of water
 Size of the city
 Industry and commerce
 Climate

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 Time of the day
 Day of the week or month
Factors Affecting Selection of Water Source
Quantity of water:
The quantity of water available at the source must be sufficient to meet various demands
and requirements of the design population during the entire design period. Plans should be
made to bring water from other sources if the available water is insufficient.
Quality of water:
The water available at the source must not be toxic, poisonous or in anyway injurious to
health. The impurities should be as minimum as possible and such that, can be removed
easily and economically.
Distance of water supply source:
The source of supply must be situated as near to the city as possible. Hence, less length of
pipes needs to be installed and thus economical transfer and supply of water. The source
nearest to the city is usually selected.
Topography of city and its surroundings:
The area or land between the source and the city should not be highly uneven i.e. it should
not have steep slopes because cost of construction or laying or pipes is very high in these
areas.
Elevation of source of water supply:
The source of water must be on a high elevation than the city so as to provide sufficient
pressure in the water for daily requirements. When the water is available at lower levels,
then pumps are used to pressurize water. This requires an excess developmental and
operational tasks and cost. It may also have breakdowns and need repairs.
Water quality
 Impurities present in water and their health significance
 Water quality standards set by U.S and W.H.O
 Water quality tests

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Sources of Fresh Water in Environmentl Engg.
Flowchart of the sources of clean drinking water
WasteWater Treatment Disposal & Management
The quantity of water required for a community depends upon:
1. Forecasted population
2. Types and variation in demand (e.g. seasonal variation)
3. Maximum demand (Per day/Per month)
4. Fire demand
5. Rural demand and supplies
6. Appropriate / Available technology
Main sources of water are
 Surface water sources: Lakes impounding reservoirs, streams, seas, irrigation canals
 Ground water sources: Springs, wells, infiltration wells
Above are the common sources of clean drinking water, other different sources of drinking
water are

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Merits of surface sources
Merits of ground water sources
1. Being underground, the ground water supply has less chance of being contaminated by
atmospheric pollution.
2. The water quality is good and better than surface source.
3. Prevention of water through evaporation is ensured and thus loss of water is reduced.
4. Ground water supply is available and can even be maintained in deserted areas.
5. The land above ground water source can be used for other purposes and has less
environmental impacts.
Demerits of ground water source
1. The water obtained from ground water source is always pressure less. A mump is required
to take the water out and is then again pumped for daily use.
2. The transport / transmission of ground water is a problem and an expensive work. The
water has to be surfaced or underground conduits are required.
3. Boring and excavation for finding and using ground water is expensive work.
4. The modeling, analysis and calculation of ground water is less reliable and based on the
past experience, thus posing high risk of uncertainty.
Chemical Characteristics of Water
1. Acidity
2. Alkalinity
3. Hardness
4. Turbidity

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Acidity:
Acidity or alkalinity is measured by pH. PH measures the concentration of Hydrogen ions
in water. Ionization of water is
HOH H+ + OH-
In neutral solutions [OH] = [H] hence pH = 7
If acidity is increased, [H] increases and pH reduces from 7 (because H is log of [H]). The
value of pH of water is important in the operations of many water and waste water treatment
processes and in the control of corrosion.
Alkalinity:
The values of pH higher than 7, shows alkalinity. The alkaline species in water can
neutralize acids. The major constituents of alkalinity (or causticity) are OH-, CO32- and
bicarbonates HCO3 ions. Alkalinity in water is usually caused by bicarbonate ions.
Hardness of water:
Definition of hard water
Hardness is the property that makes water to require more soap to produce a foam or
lather. Hardness of water is not harmful for human health but can be precipitated by
heating so can produce damaging effects in boilers, hot pipes etc by depositing the material
and reducing the water storage and carriage capacity. Absolute soft water on the other
hand is not acceptable for humans because it may cause ailments, especially to heart
patients. Hardness in water is commonly classified in terms of the amount of CaCO3
(Calcium Carbonate) in it.
Concentration of CaCO3 Degree of hardness
0 – 75 mg / L Soft
75 – 150 mg / L Moderately hard
150 – 300 mg / L Hard
300 up mg / L Very Hard
Table 1 - Degree of Hardness
Low level of hardness can be removed just by boiling but high degree of hardness can be
removed by addition of lime. This method has also the benefit that iron and manganese
contents are removed and suspended particles including micro-organisms are reduced.

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Turbidity:
Keywords: study and interpretation of the chemical characteristics of natural water,
chemical characteristics of water, chemical characteristics of natural water, water chemical
properties.
Municipal Wastewater Treatment Systems
Objectives of Wastewater Treatment
 To kill the pathogens
 To improve the quality of waste-water
 To avoid unhygienic conditions
 To protect the aquatic life from the toxicity wastes
 To make the waste water usable for agricultural, aquaculture etc
There are three constituents and interrelated aspects of waste water management.
1. Collection of Wastewater
o Collection of domestic wastewater is best achieved by a full sewerage water drain
age system. Unfortunately this method is most expensive and there is relatively few

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communities in hot climate which afford it. A modern hygienic method of night
soil collection is the only realistic alternative.
2. Treatment of Wastewater
o Treatment is required principally to destroy pathogenic agents in sewage or night
soil and to encore that it is suitable for whatever re-use process is secreted for it.
3. Re-use of wastewater (Recycling of wastewater)
o The responsible re-use of night soil and sewage effluent is aqua culture and crop
irrigation can make a significant contribution to a community food supply and
hence it’s general social development. The best example is china where over 90%
of waste after treatment is applied to land
Performance criteria for Wastewater Treatment Management System
The ideal system would satisfy all of the following criteria.
i. Health criteria
ii. Water Recycling criteria
iii. Ecological criteria
iv. Nuisance criteria
v. Cultural criteria
vi. Operational criteria
vii. Cost criteria
i. Health Criteria:
Pathogenic organisms should not be spread either by direct contact with right soil or
sewage or indirectly via soil, water or food. The treatment chosen should achieve a high
degree of pathogen destruction.
ii. Re-use/Recycle Criteria:
The treatment process should yield a safe product for re-use, preferably in aquaculture and
agriculture.
iii. Ecological criteria:
In those cases land the should be considered exception when the waste cannot be re-use,
the discharge of effluent into a surface water should not exceed the self-purification
capacity of the recipient water.
iv. Nuisance Criteria:
The degree of odor release must be below the nuisance threshold. No part of the system
should become aesthetically offensive.

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v. Cultural Criteria.
The methods chosen for waste collection, treatment and re-use should be compatible with
local habits and social (religious) practice.
vi. Operational Criteria:
The skills required for the routine operation and maintenance of the system components
must be available locally or are such that they can be acquired with only minimum training.
vii. Cost criteria:
Capital and running costs must not exceed the community’s ability to pay. The financial
return from re-use schemes is an important factor is an important factor in this regard.
However, no one system completely satisfies all these demands. The problem becomes one
of minimizing disadvantages.
Waste Water Treatment Processes
Municipal wastewater is primarily organic in content and a significant number of industries
including chemical pharmaceutical and food have high organic waste load. This means that
the main treatment processes are geared towards organic removal. In a typical treatment
plant, the wastewater is directed through a series of physical, chemical and biological
processes each with specific waste load reduction task. The tasks are typically.
1. Pre-treatment ==> Physical and / or chemical
2. Primary treatment ==> Physical
3. Secondary treatment ==> Biological
4. Advanced treatment ==> Physical and / or chemical and / or biological.
Conventional Wastewater Treatment Plant Processes
Municipal Wastewater Treatment
Conventional treatment or conventional mechanical wastewater treatment is the term used
to describe the standard method of treatment designed to remove organic matter and solid
from solution. It comprises four stages of treatment.
 Preliminary treatment ( influent flow measurement, screening (Bar racks),
Shredders, comminutors (maceratours), pumping, grit removal)
 Primary treatment (sedimentation)
 Secondary treatment (biofitration or activated sludge)
 Sludge treatment (anaerobic digestion of the sludge produced in primary and
biological treatment)

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Preliminary Treatment of Waste Water
Preliminary treatment of wastewater consists of the following steps:
1. Screening
2. Comminution
3. Grit Removal

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4. Flow Equalization
5. Oil and Grease Removal
6. Pre-Aeration
1. Screening
The first unit operation generally encountered in wastewater treatment plants is screening.
A screen is a device with openings, generally of uniform size, that is used to retain solids
found in the influent wastewater to the treatment pant. The principal role of screening is to
remove coarse materials (pieces of wood, plastics, rags, papers, leaves, roots etc.) from the
flow stream that could:
1. Damage subsequent process equipment e.g. pumps, valves, pipe lines, impellers.
2. Reduce overall treatment process reliability & effectiveness, or
3. Contaminate waste way
Design of screening chamber:
The objective of screens is to remove large floating material and coarse solids from
wastewater. It may consist of parallel bars, wires or grating placed across the flow inclined
at 30o-60o. According to method of cleaning; the screens are hand cleaned screens or
mechanically cleaned screens. Whereas, according to the size of clear opening, they are
coarse screens (≥ 50 mm), medium screens (25-50 mm) and fine screens (10-25 mm).
Normally, medium screens are used in domestic wastewater treatment.
Dimensions of an approach channel
Used in wastewater treatment is mostly rectangular in shape. Wastewater from the wet well
of the pumping station is pumped into the approach channel from where it flows by gravity

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to the treatment plant. Its main function is to provide a steady and uniform flow after
pumping.
 Select the size of bar/clear opening, say 10mm x 10 mm (medium screens)
 No. of bars; {(n + 1) + (n) = B}, and {Be = B – (width of bar)(n)}
 Head loss, hL = 0.0729 (V2 – Vh2) ------ {Vh 0.75m/sec, hL ≤ 0.5 ft}
 For perforated plate; amount of screening produce = (1-2) ft3/MG
 Length of bar; L = D/sinθ, and Lh = L * cosθ.
 Screen chamber. Lc = inlet zone (2-3 ft) + Lh + outlet zone {outlet zone = width of p
plate + (0.5-1.0 ft)}
2. Wastewater treatment through Coarse Solids Reduction:
As an alternative to coarse bar screens or fine screens, communitors and macerators be use
to intercept coarse solids and grind or shred them in the screen channel. High – speed
grinders are used in conjunction with mechanically cleaned screens to grin and shred
screenings that are cit up into a smaller, more uniform size for return to the flow stream for
subsequent removal by downstream treatment operations and processes, communitors,
macerators and grinders can theoretically eliminate the messy and offensive task of
screening handling and disposal.
Comminutors – small WWT (0.2 m3
/s or 5 MGD) 6 - 20 mm (0.25 N 0.77in)
a. Comminutors:
Comminutors are used commonly in small wastewater treatment plants having discharge
less than (0.2m3
/s or 5MGD). They are installed in a wastewater flow channel to screen and
shred material to sizes from 6 to 20 mm (0.25 to 0.77 in) without removing the shredded
solids from the flow stream. It cuts them to a relatively uniform size and prevents the solids
from freezing/clogging in the flow.
Comminutors are always placed before the grit chamber to reduce wear and tear occurring
on the surfaces.
b. Macerators:
Macerators are slow speed grinders that typically consist of two sets of counter rotating
assemblies with blades. The assemblies are mounted vertically in the flow channel. The
blades or teeth on the rotation assembles have a close tolerance that effectively chop
material as it passes through the unit.
c. Grinders:

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High speed grinders typically referred to as fiammermills, receive screened materials from
base screen. The materials are pulverized by a high speed rotation assembly that wets the
materials passing through the unit.

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3. Grit Removal system from Wastewater:
It is a Unit operation (physical). Removal of grit form waste Swater may be accomplished
in grit chambers or by centrifugal separation of solids. Grit chambers are designed to
remove grit, consisting of sand, gravel, sanders, or other heavy solid materials that have
specific gravities or setting velocities substantially greater than those of organic particles
in wastewater. Grit chambers are most commonly located after the bar screens and before
the primary sedimentation.
These are just like sedimentation tanks, design mainly to remove heavier particles or coarse
inert and relatively dry suspended solids from the wastewater. There are two main types of
grit chambers like rectangular horizontal flow types and aerated grit chambers. In the
aerated grit chamber the organic solids are kept in suspension by rising aerted system
provided at the bottom of the tank.
Purpose of Grit Chamber
Grit chambers are provided to:
1. Protect moving mechanical equipment from abrasion and accompanying abnormal wear.
2. Reduce formation of heavy deposits in pipelines, channels and conduits.
3. Reduce the frequency of digester.
Flow Equalization tank

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Flow equalization is method used to overcome the operational problems and flow rate
variations to improve the performance of downstream processes and to reduce the size &
cost of downstream treatment facilities. To prevent flow rate, temperature, and contaminant
concentrations from varying widely, flow equalization is often used. It achieves its
objective by providing storage to hold water when it is arriving too rapidly, and to supply
additional water when it is arriving less rapidly than desired. A smaller the screen opening,
greater will be the amount of material screened.
In order to improve the performance of a reactor, particularly the biological processes, it
is required to equalize the strength of wastewater and to provide uniform flow, an
equalization tank is design after screen and grit chamber. This may be in the line-off or
off-line, as shown in the figure;
5. Primary Sedimentation Tank
Sedimentation or setting tanks that receive raw wastewater prior to biological treatment are
called primary tanks. The objective of the primary sedimentation tank is to remove readily
settleable organic solids and floating material and thus reduce the suspended solid content.
Efficiently designed and operated primary sedimentation tanks should remove from 50 to
70% the suspended solids and 25 to 40% of the BOD.

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Sedimentation is carried out in variety of tank configurations including:
 Circular sedimentation tank
 Rectangular sedimentation tank
 Square sedimentation tank
Primary sedimentation is among the oldest wastewater treatment process. Traditionally the
design criteria for sizing setting tanks are:
Average overflow rate: 30 - 50 m3
/m2
/d (Typical 40 m3
/m2
/d) [800-1200 gal/ft2
-d
(Typical 1000 gal/ft2
-d]
Peak hourly overflow rate: 50 - 120 m3
/m2
/d (Typical 100 m3
/m2
/d) [2000-3000 gal/ft2
-d
(Typical 2500 gal/ft2
-d]
Weir loading rate: 1.5 - 2.5h (Typical 2.0 h) [1.5 - 2.5 h (Typical 2.0h)]
Types of Primary Sedimentation Tanks
Primary Sedimentation takes place in the sedimentation tanks with the objective to remove
readily settleable solids and floating materials and thus reduce the suspended solids
content. The removal rate is 50-70% of suspended solids and 25-40% of BOD whereas,
generally more than two rectangular or circular tanks are used.

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Rectangular Horizontal Flow Tanks
These are most commonly used for primary sedimentation, since they
 Occupy less space than circular tanks.
 They can be economically built side-by-side with common walls.
 Length ranges 15 to 100m an width from 3 to 24m (length/ width ratio 3:1 to 5:1)
 The maximum forward velocity to avoid the risk of scouring settled sludge is 10 to 15
mm/s (06 to 09m/min or 2 to 3 ft/ min), indicating that the ratio of length to width l/w
should referrals be about.
 The maximum weir loading rate, to limit the influence of draw-down currents, is preferably
about 300 m3
/d-m, this figure is sometime increased where the design flow is great then 3
ADWF.
 Inlets should be baffled to dissipate the momentum of the incoming flow and to assist in
establishing uniform forward flow.
 Sludge is removed by scraping it into collecting hoppers at the inlet end of the tank.
 Some removal is essential in primary sedimentation tanks because of the grease and other
floating matter which is present in wastewater. The sludge serapes can return along the
length of the tank a the water surface. As they move towards the outlet end of the bank, the
flights then move the sum towards a skimmer located just upstream of the effluent weirs.
Rectangular Sedimentation Tank
Circular Radial Flow Tanks
These are also used for primary sedimentation.
 Most common-have diameters from 3 to 60m (side water depth range from 3 to 5m)
 Careful design of the inlet stilling well is needed to active a stable radial flow pattern
without causing excessive turbulence in the vicinity of the central sludge hopper.

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 The weir length aroid the perimeter of the tank is usually sufficient to give a sates
factory weir loading rate at maximum flow, but at low flows, very low flow depths
may result.
 To overcome the sensitivity of these tanks to slight errors in weir level and wind
effects, it is common to provide v-much wares.
 Sludge removal is effected by means of a rotary sludge scrapper who moves the
sludge into a central hopper, form which it is with drown.
 Scum removal is carried out by surface skimming board attached to the sludge
scrapper mechanism and positioned so that scum is moved towards a collecting
hopper at the surface.
Up Flow Tanks:
 Up flow tanks, usually square in plan and with deep hopper bottoms, are common
in small treatment plants.
 Their main advantage is that sludge removal is cared out entirely by activity and no
mechanical parts are required for cleaning them.
 The steeply sloping sides usually to to horizontal concentrate the sludge at the
bottom of the hopper.
 Weir loading rate is a problem only at low flows. So that v-match weirs are
desirable.
 The required up flow pattern is maintained by weir troughs.
 True up flow tanks have an disadvantage on that hydraulic over loading may have
more serious effects than in horizontal flow tanks.
 Any practical with a velocity lower than VP = Q/A will not removed in an up flow
tank, but will escape in the effluent.
 In a horizontal flow tank assuming that such particles were uniformly distributed to
the flow, particle with Vp=Q/A still be removed in proportion.
Square sedimentation tank
They may be flat bottomed or hopper bottomed. Wastewater enters the tanks, usually at the
center, through a well or diffusion box. The tank is sized so that retention time is about 24
(range 20 minutes to 3h). In the quiescent period, the suspended part ides settle to the
bottom as sludge and are raked towards a central hopper from where the sludge is
withdrawn.
Primary sedimentation is among the oldest wastewater treatment process. Traditionally the
design criteria for sizing setting tanks are:
Average overflow rate: 30 - 50 m3
/m2
/d (Typical 40 m3
/m2
/d) [800-1200 gal/ft2
-d
(Typical 1000 gal/ft2
-d]

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Peak hourly overflow rate: 50 - 120 m3
/m2
/d (Typical 100 m3
/m2
/d) [2000-3000 gal/ft2
-d
(Typical 2500 gal/ft2
-d]
Weir loading rate: 1.5 - 2.5h (Typical 2.0 h) [1.5 - 2.5 h (Typical 2.0h)]
Rectangular Sedimentation Tanks Circular Sedimentation Tanks
Depth
10-16 ft (Typical 14) 3 - 3.9 m
(Typical 4.3)
10-6 (Typical 14)3.39m (Typical 4.3 m)
Length 50-300 ft (Typical 80-30 ft)
Diameter 10-200 (Typical 40-150ft) 3-
60 m (Typical 12-45m
Flight speed
2-4 ft/min (Typical 3 ft/min) or
(Typical 0.9 m/min)
Scraper’s speed 0.02-0.05/min (Typical
0.03 Rev/min)
Bottom
Slope
1in/ft or Typical 0.9m/m check 1.12 ft
 Always provide minimum of 2 sedimentation tanks.
 Sludge accumulation is same for both.
 Sludgy accumulation 2.5kg of wet solids per m3
of flow.
Secondary Biological Wastewater Treatment
Process

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1. Objectives of Secondary Treatment of waste water
Main objective
The main objective of secondary treatment: To remove most of the fine suspended and
dissolved degradable organic matter that remains after primary treatment, so that the
effluent may be rendered suitable for discharge. Conventional secondary treatment can
reduce the BOD's to below 20mg/l and Suspended Solids to below 30mg/l which is
acceptable in many cases.
Second objective
The second objective of secondary treatment: The reduction of ammonia toxicity and
nitrification oxygen demand in the stream. This is achieved by oxidation of most of the
ammonia to nitrate during treatment (nitrification).
2. Nitrification:
Means the oxidation of ammonia to nitrate. Nitrification is possible with aerobic biological
processes. If they are operated at low organic load rates-hence the units must be large than
those which would be required for oxidation of carbonaceous matter alone.
1. Conventional sedimentation the major process in primary wastewater treatment, normally
removes 60 to 70 % of suspended solids matter containing 30% to 40% of the BOD present
in municipal wastewater, leaving 150 to 200 mg/ l of BOD's and about 100mg/l SS in the
primary effluent.
2. Discharge or effluent of this quality with exceeding the assimilative capacity of the
receiving the assimilative capacity of the receiving environment is only possible where
very large volumes of water are available for delectation or where the effluent may be
irrigated over a large land area.
3. For discharge to inland streams or lakes, a considerably higher quality is necessary.
Assimilative capacity of O2 in H2O = 9mg/l not less then 2mg/l.
Biological Wastewater Treatment Processes
1. Aerobic biological processed
2. Anaerobic biological processed
3. Facultative biological processed
1. Aerobic Biological Processes
Are those where sufficed amount of dissolved oxygen is required into the wastewater to
sustain aerobic action, as one of the major polluting effects of wastewater on streams results
form the depletion of dissolved oxygen by the action of aerobic organisms in degrading the
organic content of the waste. Practical aerobic biological treatment processes seek to to

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this, within the constraints of available land area and economic resources available to
construct and operate treatment works.
2. Anaerobic Biological Processes
Are those where micro-organisms oxidize organic matter in the completed absence of
dissolved oxygen. The micro-organisms take oxygen form inorganic salts which contain
bound oxygen (Nitrate NO3, Sulphate So4
2-
, Phosphate PO4
2-
). This mode of operation is
termed as anaerobic processes. Sufficiently fore dissolved oxygen is either physically
difficult or economically impracticable to transfer into the wastewater to sustain aerobic
action to biodegrade strong organic wastes.
Tip: Assimilative capacity of BOD in water is not more than or should be less then 4mg/l.
Aerobic Biological Treatment Processes
There are five types of aerobic biological treatment processes used to treat municipal
sewage
1. Tricking filters
2. Rotating biological contactors (filter)
3. Activated sludge.
4. Oxidization ponds.
5. Aerated lagoons (used for pre treat ion industrial effluent)
Trickling Filter
Introduction to trickling filter system:
It is the most common attached growth process. The trickling filter is like a circular well
having depth up to 2 meter filled with granular media like stone, plastic sheets and
redwood, slag, slate. The first tricking filter was placed in operation in England in 1893.
the concept of a tricking filter was grew form the of contact frets which were water tight
basins filled with broken stones. The limitation the contact filters included a relatively.
 Wastewater is distributed over top area of vessel containing non-submerged packing
material;
 Historically, rock was used with typical depths 1.25‐ 2 m
 Modern trickling filters 5 to 10 m and filled with plastic packing material for biofilm
attachment;
 90‐95% of volume in tower consists of void space;
 Air circulation in void space provides oxygen for microorganisms growing as attached
biofilm;

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 Excess biomass sloughs from attached growth periodically and clarification is required for
liquid/solids separation
 High incidence of clogging,
 The long retention time (a typical cycle required 12 hours, 6 hours for operation and 6
hours for resting) and relatively
 Low loading rate. life cycle/ biological circle of bacteria: 20-30 mints. The tricking filter
itself consists of a bed of coarse material, such as stones, slates or plastic materials (media)
over which wastewater is applied. Because the micro-organisms that biodegrade the waste
form a film on the media this process is known as an attached growth process.
Tricking filters have been a popular biological treatment processes the must widely used
design for many years are:
Design diameter of Rock filters = 60m (2007t) and for Rock size Design diameter = 25 to
100mm
Activated Sludge Process
 It involves production of activated mass of microorganisms capable of stabilizing waste
under aerobic conditions;
 In aeration tank, contact time is provided for mixing and aerating influent wastewater with
microbial suspension, generally referred to mixed liquor suspended solids (MLSS) or
mixed liquor volatile suspended solids (MLVSS)
 Mixed liquor than flows to clarifier where microbial suspension is settled and thickened;
 Settled biomass (activated sludge) is returned to aeration tank to continue biodegradation
of influent;
 Portion of thickened solids is removed daily or periodically as process produces excess
biomass;
 Formation of floc particles, ranging in size from 50 to 200 μm, removed by gravity settling,
leaving relatively clear liquid as treated effluent;
 Typically 99% of suspended solids removed by clarification step;
Biological Treatment systems
1. Attached growth processes
2. Suspended growth processes
3. Dual (hybrid) biological treatment processes.
Attached growth process
 Microorganisms responsible for conversion of organic material or nutrients are attached
to an inert packing material;
 Organic material and nutrients are removed from wastewater flowing past attached
growth also known as biofilm
 Packing materials used in attached growth processes include rock, gravel, slag, sand,
redwood and wide range of plastic and other synthetic materials

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Suspended Growth (SG) Processes
 Microorganisms responsible for treatment are maintained in liquid suspension by
appropriate mixing methods;
 Many SG processes are operated with positive dissolved oxygen concentration;
 Most common SG process is activated sludge process
Activated Sludge Wastewater Treatment Process
It is a:
 Unit process
 Biological treatment process
 Suspended growth process
 Aerobic process
Activated Sludge:
Definition
Is defined as a ‘Suspension’ of microorganisms, both living and dead’ in a wastewater.
The microorganisms are active by an input of air (oxygen) thus known as activated-sludge.

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Activate-sludge is that sludge which settle down in a secondary sedimentation tank after
the sewage has been freely aerated and agitated for a certain time in an Aeration tank.
Working Mechanism of Activated Sludge
The activated-sludge contains numerous bacteria and other microorganisms, when it is
mixed with raw sewage saturated with oxygen, the bacteria perform the following function.
1. Oxidize the organic solids.
2. Promote coagulation and flocculation and convert dissolved, colloid and suspended solids
into settle able solids. In practice the following operations are carried out in an activated -
sludge process.
3. The sewage is given treatment in the primary sedimentation tank. The detention time is
kept as short as 1-1/2 hours.
4. The settled sewage form the Primary Sedimentation Tank is the mixed with the required
quantity of activated-sludge in the aeration tank. The mixture of activated-sludge and
wastewater in the aeration tank is called ‘mixed liquor or mixed liquor suspended
solids MLSS or MLVSS mixed liquor volatile suspended solids’.
5. The Mixed Liquor Suspended Solids is aerated for 6-8 hours in the aeration tank, called
the hydraulic detention timeaccording to the degree of purification. About 8m3
of air is
provided from each m3 of waste-water treated. The volumes of sludge returned to the
aeration basin is typically 20 to 30% of waste water flow air supply 8-10 m3
of sewage
6. The aerated Mixed Liquor Suspended Solids resulting in the formation of flock particles,
ranging in size from 50 to 200pm.which is then removed in the secondary sedimentation
tank by gravity settling, leeching a relatively clear liquid as the treated effluent. Typically
greater than 99% of suspend solids can be removed in the clarification step.
7. Most of the settled sludge is returned to the aeration tank (and is called return sludge) to
maintain the high population of microbes that permits rapid breakdown of the organic
compounds. Because more activated-sludge is produced tan is desirable in the process,
some of the return sludge is diverted or wasted to the sludge handling system for treatment
and disposal.
Activated Sludge Process
Consists of three basic components:

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1. Reactor in which microorganisms responsible for treatment are kept in suspension and
aerated;
2. Liquid-solids separation usually in sedimentation tank;
3. Recycle system for returning solids removed from liquid-solids separation unit back to
reactor;
Important feature is formation of flocculent settleable solids removed by gravity settling in
sedimentation tanks. Pretreatment with primary sedimentation removes settleable solids
whereas biological processes remove soluble, colloidal, and particulate (suspended)
organic substances; for biological nitrification and denitrification; and for biological
phosphorus removal.
Activated Sludge Process Design
Design of Activated Sludge Systems:
Design of activated-sludge process involves details of sizing and operation
of the following main elements.
1. Aeration tank (reactor)-capacity and dimensions.
2. Aeration system-oxygen requirements and oxygen transfer system.
3. Final sedimentation tank – (deifier)
4. Return activated sludge system.SV1
5. Excess activated sludge withdrawal system and subsequent treatment and
disposal of waste sludge. Since the whole process takes place in a liquid medium
the hydraulic regime essentially in the aeration tank and final sedimentation tank.
6. MLSS – a mixture of settled sewage + activated sludge dissolved oxygen < 2mg/l
Design Criteria
1. F/M ratio = 0.2 – 0.5 day -1 or 0.2 – 0.5 kg BOD's / kg MLSS – d
2. Detention time (aeration time) of sewage = 6 to 6 hours
3. MLVSS or MLSS = 1500 -3000 mg/l
4. Air supply = 10m3/m3 sewage treated
5. return sludge = 0.25 -10 of Q (influent sewage flow) Qr / Q = 0.20-0.30 =
Vs/100Vs (Volume of sludge)
6. Depth = 3-5m
7. L=W ratio =5:1
8. SVI 50-150 ml/gm
Bacterial Classification in Wastewater Treatment

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Microbiology in Waste Water Treatment:
It is the branch of biology which deals with micro organisms which is unclear or cluster of
cell microscopic organisms.
MICROORGANISMS:
Microorganisms are significant in water and wastewater because of their roles in different
transmission and they are the primary agents of biological treatment. They are the most
divers group of living organisms on earth and occupy important place in the ecosystem.
Are called OMNIPRESENT.
Classification of Bacteria in Waste Water Treatment Process
1. Classification of bacteria based on Oxygen requirements (ORP)
The heterotrophic bacteria are grouped into three classification, depending on their action
toward free oxygen (O4) or more precisely oxygen-reduction potential (ORP) for survival
and optimum growth.
1. Obligate aerobe or Aerobes or bacteria are micro-organisms require free dissolved oxygen
to oxidize organic mate and to live and multiply. These conditions are referred to as aerobic
processes.
2. Anaerobes or anaerobic bacteria are micro-organisms oxidize organic matter in the
complete absence of dissolved oxygen. The micro-organisms take oxygen from inorganic
sates which contain bound oxygen (Nitrate NO3, Sulphate So4
2-
, Phosphate PO4
2-
). This
mode of operation is termed as anaerobic process.
3. Facultative bacteria are a class of batter that use free dissolved oxygen when available but
can also Respire and multiply in the absence. "Escherichia Coli" a facile coli from is a
facultative elaterium. (Facultative Bacteria = Aerobic anaerobic bacteria)
2. Classification of Microorganisms by Kingdom:
Microorganisms are organized into five broad groups based on their structural functional
differences. The groups are called “Kingdoms”. The five kingdoms are animals, plants,
protista fungi and bacteria.
Representative examples and characteristics of differentiation are shown:

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3. Classification by their preferred Temperature Regimes:
Each specie of bacteria reproduces best within a limited range of temperatures. Four
temperature ranges for bacteria:
1. That best at temperatures below 20°C are called psychrophiles.
2. Grows best in between 25°C and 40°C are called Mesophiles.
3. Between 45°C and 60°C thermopiles can grow.
4. Above 60 °C stenothermophiles grow best.
BACTERIA: