Sewage

1. INTRODDUCTION
Thisstudyaimsto harnessrain waterthroughrainwater harvesting
systemaffordable byall segmentsof society.The studywasmade by
identifyingthe characteristicsof waterandrainwaterharvestingto
ensure qualitycompliance with waterqualitystandardssetbythe
Departmentof Environment(DOE).However,the industrial
developmentandgrowingcause rainwatercontainspollutantsthat
can affecthumanor livingthinghealth.Therefore,the ideaof usinga
filterthatmade of natural materialsshouldbe appropriatetoeliminate
or reduce generatedpollutantsfoundinrainwaterandtomake it
affordable byusers.
issues for
Water, food and energy securities are emerging as increasingly important and vital issues for
Bangladesh and the world. Most of the river and canals in Bangladesh is polluted and
experiencing moderate to severe water shortages, brought on by the simultaneous effects of
agricultural growth, industrialization and urbanization. Sewage is a major point source of
pollution. Current and future fresh water demand could be met by enhancing water use efficiency
and demand management. Thus, wastewater/low quality water is emerging as potential source
for demand management after essential treatment. Also, sewage can be viewed as a source of
water that can be used for various beneficial uses including ground water recharge through
surface storage of treated water and/or rain/flood water in an unlined reservoir. In order to reduce
substantial expenditure on long distance conveyance of sewage as well as treated water for
recycling, decentralized treatment of sewage is advisable. Sewage / wastewater treatment consist
of different processes which protect the environment & human through cleansing the water
pollutant.
Sewage is the wastewater generated by a community, namely: a) domestic wastewater, from
bathrooms, toilets, kitchens, etc., b) raw or treated industrial wastewater discharged in the
sewerage system, and sometimes c) rain-water and urban runoff. Domestic wastewater is the
main component of sewage, and it is often taken as a synonym. The sewage flow rate and
composition vary considerably from place to place, depending on economic aspects, social
behavior, type and number of industries in the area, climatic conditions, water consumption, type
ofsewers system, etc. The main pollutants in sewage are suspended solids, soluble organic
compounds, and fecal pathogenic microorganisms, but sewage is not just made up of human
excrement and water. A variety of chemicals like heavy metals, trace elements, detergents,
solvents,pesticides, and other unusual compounds like pharmaceuticals, antibiotics, and
hormones can alsobe detected in sewage. With urban runoff come potentially toxic compounds
like oil from cars andpesticides that may reach the treatment plant and, eventually, a water body.

2. Sewage treatment is a multi-stage process designed to treat sewage and protect natural water
bodies. Municipal sewage contains various wastes. If improperly collected and improperly
treated, this sewage and its related solids could hurt human health and the environment. A
treatment plant’s primary objectives are to clean the sewage and meet the plant’s discharge
standards The treatment plant personnel do this by reducing the concentrations of solids, organic
matter, nutrients, pathogens and other pollutants in sewage. The plant must also help protect the
receiving water body, which can only absorb a certain level of pollutants before it begins to
degrade, as well as the human health and environment of its employees and neighbours. One of
the challenges of sewage treatment is that the volume and physical, chemical, a limited quantity
of pollutants and biological characteristics of sewage continually change. Some changes are the
temporary results of seasonal, monthly, weekly or daily fluctuations in the sewage volume and
composition. Other changes are long-term, being the results of alterations in local populations,
social characteristics, economies, and industrial production or technology. The quality of the
receiving water and the public health and well-being may depend on a treatment plant operator’s
ability to recognize and respond to potential problems. These responsibilities demand a thorough
knowledge of existing treatment facilities and sewage treatment technology.
COMPOSITION OF SEWAGE
1.1CLASSIFICATION OF SEWAGE
Sewage may be classified mainly into three types, namely, domestic sewage, industrial sewage,
and storm sewage.
Sewage
Water
(99.9)
Solids
(0.01)
Organic
(70)
Proteins
(65)
Carbohydrate
(25)
Fats (10)
Inorganic
(30)
Grit
Metals

3. 1.4.1 Domestic or Sanitary Sewage
Domestic sewage consists of liquid wastes originating from urinals, latrines, bathrooms, kitchen
sinks, wash basins, etc. of the residential, commercial or institutional buildings. This sewage is
generally extremely foul, because of the presence of human excreta in it.
1.4.2. Industrial Sewage or Wastewater
Industrial sewage consists of liquid wastes originating from the industrial processes of various
industries, such as Dyeing, Paper making, brewing, etc. The quality of the industrial sewage
depends largely upon the type of industry and the chemicals used in their process waters.
Sometimes, they may be very foul and may require extensive treatment before being disposed of
in public sewers.
1.4.3. Storm Sewage
Storm sewage means water that is discharged from a surface as a result of rainfall, snow melt or
snowfall.
WHY TREAT WASTEWATER?
 It's a matter of caring for our environment and for our own health.
 To prevent groundwater pollution
 To prevent sea shore
 To prevent marine life
 Protection of public life
 To reuse the treated effluent, for agriculture, for groundwater recharge, for industrial
recycle
 Solving social problem caused by the accumulation of wastewater.
If wastewater is not properly treated, then the environment and human health can be negatively
impacted.
1.1WASTEWATER CHARACTERISTICS
Wastewater is characterized in terms of its:
 Physical
 Chemical
 Biological
1.6.1 PhysicalCharacteristicsofWastewater
The physical characteristics of wastewater are based on color, odor, temperature, solids and
turbidity.
 Color: Fresh wastewater is usually a light brownish-gray color. However, typical
wastewater is gray and has a cloudy appearance. The color of the wastewater will change

4. significantly if allowed to go septic (if travel time in the collection system increases).
Typical septic wastewater will have a black color.
 Odor: Fresh domestic wastewater has a musty odor. If the wastewater is allowed to go
septic, this odor will significantly change to a rotten egg odor associated with the
production of hydrogen sulfide (H2S).
 Temperature: The temperature of wastewater is commonly higher than that of the water
supply because of the addition of warm water from households and industrial plants.
However, significant amounts of infiltration or storm water flow can cause major
temperature fluctuations. The ideal temperature of sewage for the biological activities is
20°c.
 Solids: All the materials in the liquid except water are called as solids. Solids are classified
into three main types. All the matter that remains as residue upon evaporation at 103̊ C to
105̊ C is called total solids. Those solids that are not dissolved in wastewater are called
suspended solids. When suspended solids float, they are called floatable solids or scum.
Those suspended solids that settle are called settleable solids, grit, or sludge. All solids that
burn or evaporate at 500°C to 600°C are called volatile solids. Those solids that do not
burn or evaporate at 500°C to 600°C, but remain as a residue, are called fixed solids. Fixed
solids are usually inorganic in nature and may be composed of grit, clay, salts, and metals.
 Turbidity: Turbidity is a measure of water clarity how much the material suspended in
water decreases the passage of light through the water.
2 ChemicalCharacteristics ofWastewater
Chemical characteristics of wastewater are: organic matter, measurements of organic matter,
inorganic matter, gases, pH.
 pH: This is a method of expressing the acid condition of the wastewater. pH is expressed
on a scale of 1 to 14. For proper treatment, wastewater pH should normally be in the range
of 6.5 to 9.0. The determination of pH value of sewage is important, because of the fact
that efficiency of certain treatment methods depends upon the availability of a suitable pH
value.
 Gases: These are gases that are dissolved in wastewater. The specific gases and normal
concentrations are based upon the composition of the wastewater. Typical domestic
wastewater contains oxygen in relatively low concentrations, carbon dioxide, and hydrogen
sulfide.
 Inorganic Matter: The main inorganic materials of concern in wastewater are chloride,
nitrogen, phosphorus, sulfur, toxic inorganic compounds, and heavy metals.
 Organic Matter: Organic matter consists of Carbohydrates such as cellulose, cotton, fiber,
starch, sugar, etc. Fats and oils received from kitchens, laundries, garages, shops, etc.
Nitrogenous compounds like proteins and their decomposed products.
 Oxygen Demand: There are three ways of expressing oxygen demand as like as
Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Theoretical
Oxygen Demand (ThOD).

5. 1.6.3 BiologicalCharacteristicsofWastewater
The biological characteristics of sewage are due to the presence of bacteria and other living
microorganisms, such as algae, fungi, protozoa, etc. The former are more active.
CHARACTERIZATION OF SEWAGE
Wastes are usually treated by supplying them with oxygen so that bacteria can utilize the waste
as food.
The general equation is:
Waste+ Oxygen bacteria Treated waste + new bacteria
OXYGEN DEMAND
The amount of oxygen used by bacteria and other wastewater organisms as they feed upon the
organic solids in the wastewater.
There are three ways of expressing oxygen demand
1. Theoretical Oxygen Demand (ThOD)
2. Biochemical Oxygen Demand (BOD)
3. Chemical Oxygen Demand (COD)
TheoreticalOxygenDemand
Theoretical oxygen demand is the amount of oxygen required to oxidize the organic fraction of
the wastewater completely to carbon dioxide and water. The equation for the total oxidation of,
say, glucose is:
C6H12O6 + 6O2 → 6CO2 +6H2O
With C = 12, H = 1 and O = 16, C6H12O6 is 180 and 6O2 is 192; we can thus calculate that the
ThOD of, for example, a 300 mg/l solution of glucose is 1.07∗300 = 321 mg/l. Because
wastewater is so complex in nature its ThOD cannot be calculated, but in practice it is
approximated by the chemical oxygen demand.
ChemicalOxygen Demand (COD)
Chemical oxygen demand (COD) is the amount of chemical oxidation required to convert
organic matter in water and wastewater to carbon dioxide. The chemical oxygen demand (COD)
of a raw water or a wastewater is determined by performing a laboratory test on the given
wastewater with a strong oxidant like dichromate solution; and the theoretical computations of
COD are only performed on water solutions prepared with the known amounts of specific

6. organic compounds in laboratory situations to compare the theoretical and test results, and to
establish the limitations of the test procedures.
The laboratory determination of COD, as said above, lies in using a strong oxidant like
potassium dichromate (K2Cr2O7) or potassium permanganate (KMnO4) solution to stabilize the
organic matter to determine the molecular oxygen used from the oxidant solution in oxidizing the
organic matter present in the given wastewater.
In order to perform this test, a known quantity of wastewater is mixed with a known quantity of
standard solution of potassium dichromate, and the mixture is heated. The organic matter is
oxidized by K2Cr2O7 (in the presence of H2SO4 (helps to digest/break down the complex
molecules)). The resulting solution of K2Cr2O7 is titrated with standard ferrous ammonium
sulphate [Fe(NH4)2.(SO4)2.6H2O)], and the oxygen used in oxidizing the wastewater is
determined. This is called the chemical oxygen demand (COD) and is a measure of organic
matter present in sewage.
The advantage of COD measurements is that they are obtained very quickly (within 3 hours), but
they have the disadvantages that they do not give any information on the proportion of the
wastewater that can be oxidized by bacteria, nor on the rate at which bio-oxidation occurs.
Biochemicaloxygendemand (BOD)
Biochemical oxygen demand is used as a measure of the quantity of oxygen required for
oxidation of biodegradable organic matter present in the wastewater by aerobic biochemical
action. The BOD value is most commonly expressed in milligrams of oxygen consumed per liter
of sample during 5 days of incubation at 20 °. The rate of oxygen consumption in a wastewater is
affected by a number of variables: temperature, pH, the presence of certain kinds of
microorganisms, and the type of organic and inorganic material in the wastewater. BOD directly
affects the amount of DO within the wastewater.
BOD Removal Kinetics
First-order kinetics
The rate at which organic matter is oxidized by bacteria is a fundamental parameter in rational
design of biological waste treatment processes. It has been found that BOD (Biochemical
Oxygen Demand) removal often approximates first-order kinetics; that is, the rate of BOD
removal (= the rate of oxidation of organic matter) at any time is proportional to the amount of
BOD present in the system at that time. Mathematically this type of reaction is written as:
=-K1L …………... (1)
Where, L is the amount of BOD remaining (= organic matter still to be oxidized) at time t, and
K1 is the first order constant rate for BOD removal, which has the units of reciprocal time,
usually day-1
The differential co-efficient is the rate at which the organic matter is oxidized and the minus
sign indicates a decrease in the value of L with time. Equation (1) is the differential form of the
first-order equation for BOD removal, it can be integrated to

7. L=Loe-K1t................... (2)
Where Lo is the value L at t=o, Lo is the amount of BOD in the system before oxidation occurs,
it is therefore the ultimate BOD. The amount of BOD removed or satisfied (= organic matter
oxidized) plus the amount of BOD remaining (=organic matter yet to be oxidized) at any time
must obviously equal the ultimate BOD (= initial amount of organic matter)
Y=Lo-L..................... (3)
Where, y is the BOD removed at time t
Substitution of equation (3) into equation (2) yields
Y=Lo (1-e-k1t)
for analyzing BOD data to determine obtain estimates of the values k1 and Lo are given in
Appendix 2
Equation 2 can be written in the form:
L=Lo10-k1t
Where K1=k1/2.3
Because of the confusion that generally arise K1 and k1, it is always best to give the base when
quoting k1 values e.g. 0.23 (base e), o.10 (base 10)
1.2DEFINITION OF MICROBIOLOGY
Microbiology is the study of microscopic organisms, such as bacteria, fungi, and protozoa. It also
includes the study of viruses, which are not technically classified as living organisms but do
contain genetic material. Microbiology research encompasses all aspects of these
microorganisms such as their behavior, evolution, ecology, biochemistry, and physiology, along
with the pathology of diseases that they cause.
An organism that can be seen only with aid of a microscope and that typically consists of only a
single cell. Microorganism includes bacteria, protozoa, algae, fungi, viruses and pathogenic
microorganisms groups.
1.3BRANCHES OF MICROBIOLOGY
Microbiology can be classified into
 Pure microbiology
 Applied microbiology
1.11.1 Pure microbiology
 Bacteriology (Study of bacteria)
 Mycology (Study of fungi)

8.  Protozoology (Study of protozoa)
 Phycology
 Parasitology
 Immunology
 Virology (Study of viruses)
 Nematology
 Microbial cytology
 Microbial physiology
 Microbial ecology
 Microbial genetics
 Cellular microbiology
 Evolutionary microbiology Generation microbiology
 Systems microbiology
 Molecular microbiology
 Nano microbiology
 Biological agent
 Agrology (Study of algae)
1.11.2 Applied microbiology
 Medical microbiology
 Pharmaceutical microbiology
 Industrial microbiology
 Microbial biotechnology
 Food microbiology
 Agricultural microbiology
 Plant microbiology and Plant pathology
 Soil microbiology
 Veterinary microbiology
 Environmental microbiology
 Water microbiology
 Aero microbiology
1.4MICROBES AND ITS IMPORTANCE IN SEWAGE TREATMENT
 Microbes have an important role in sewage treatment. The most important microbes are
bacteria, viruses, algae, and protozoa. The stabilization of organic matter is accomplished
biologically using a variety of microorganisms

9. 1.5 BACTERIA
Bacteriais a single celledorganismwhichcanbe foundonmostmaterialsandsurfacesandexistas
single cell,inpair,chainsorcluster.Theyare verysmall insize andneeda microscope tosee. Theyare
unicellularorganisms,someare free-livingorganismsandsome are parasitic.Free-livingbacteriause
flagellaformovementandsome are toxins.Theyare prokaryoticorganismi.e.theirnucleusesare not
boundedbymembrane.
1.5.1 Shapes of Bacteria
Most bacterial speciesare eitherspherical,calledcocci (sing.coccus,fromGreekkókkos,grain,seed),or
rod-shaped,calledbacilli(sing.bacillus,fromLatinbaculus,stick).Somebacteria,calledvibrio,are
shapedlike slightlycurvedrodsorcomma-shaped;otherscanbe spiral-shaped,calledspirilla,ortightly
coiled,calledspirochaetes.
1.5.2 Type of Bacteria
1.13.2.1 Based on Environment
Variousbacteriathrive invariedenvironment.While some speciescanwithstandextreme conditions,
othersneedspecificmoderate conditionstosurvive.Basedonthe preference of environmental
conditionsfortheirhabitat,bacteriaare classifiedinto:
 Halophiles - Those which can survive in highly saline conditions.
 Thermophiles - Those which can resist high temperature.
 Acidophiles - Those which can tolerate low pH conditions.
 Neutrophiles - Those which require moderate conditions to survive.
 Mesophiles - Those which require moderate conditions to survive.
 Extremophiles - Those which can survive in extreme conditions.
 Alkaliphiles - Those which can tolerate high pH conditions.
 Psychrophilic bacteria - Those which can survive extremely cold conditions.
 Osmophiles - Those which can survive in high sugar osmotic conditions.
1.13.2.2 Based on RequirementofOxygen
Bacteriaare alsoclassifiedbasedonthe requirementof oxygenfortheirsurvival.
 Aerobic bacteria - Bacteria that need oxygen for their survival
 Anaerobic bacteria - Bacteria that do not require oxygen for survival.
1.13.2.3 Based on Cell Wall Contents(StainingMethods)
 Gram-positive bacteria - The thick layer of Peptidoglycans is stained purple by the crystal
violet dye, which is why gram-positive bacteria appear purple or blue
 Gram-negative bacteria - The thin layer of Peptidoglycans cannot retain the crystal violet
dye, and thus appear red or pink due to the retention of the counter-stain.
1.13.2.4 Based on Disease Producing Characteristics

10.  Pathogenic bacteria – This bacteria is the cause of diseases like typhoid, dysentery, cholera
etc.
 Non-pathogenic bacteria – This is the bacteria which do not caused any disease.
1.13.2.5 Based on Formation of Spores
Some bacteriaformendospores,whichare extremelytoughandimpenetrable outershells,when
exposedtounfavorableconditions.These endosporesenable the bacteriatosurvive theseconditionsby
remaininginadormant state.Whenthe conditionsare favorable,the bacteriaagainreverttotheir
original state.Endosporescanhelpbacteriasurviveformillionsof yearsinadormantstate.
Basedon whetherbacteriaformendosporesornot,theyare classifiedintothe followingtwotypes.
 Endospore forming bacteria
 Non-endospore forming bacteria.
1.5.3 Coliform Bacteria
Coliformbacteriaare definedasrod-shapedGram-negative non-spore formingandmotileornon-motile
bacteriawhichcan fermentlactose withthe productionof acidandgas whenincubatedat35–37°C.
Theyare a commonlyusedindicatorof sanitaryqualityof foodsandwater.Coliformscanbe foundin
the aquatic environment, insoil andonvegetation;theyare universallypresentinlarge numbersinthe
fecesof warm-bloodedanimals.Whilecoliformsthemselvesare notnormallycausesof seriousillness,
theyare easyto culture,andtheirpresence isusedtoindicate thatotherpathogenicorganismsof fecal
originmaybe present.Suchpathogensinclude disease-causingbacteria,viruses,orprotozoaandmany
multicellularparasites.Coliformproceduresare performedinaerobicrespirationaerobicoranaerobic
conditions.
1.5.4 Types of Coliform Bacteria
There are three typesof coliformbacteria
 Total coliform bacteria
 Fecal coliform bacteria
 Escherichia coli or E. coli bacteria
1.13.4.1 Total ColiformBacteria
Total coliformsinclude bacteriathatare foundinthe soil,inwaterthat hasbeeninfluencedbysurface
water,and inhumanor animal waste.
1.13.4.2 Fecal ColiformBacteria
Fecal coliformsare the groupof the total coliformsthatare consideredtobe presentspecificallyinthe
gut and fecesof warm-bloodedanimals.Becausethe originsof fecal coliformsare more specificthanthe
originsof the more general total coliformgroupof bacteria,fecal coliformsare consideredamore
accurate indicationof animal orhumanwaste thanthe total coliforms.
1.13.4.3 E. Coli Bacteria

11. Escherichiacoli (E.coli) are the major speciesinthe fecal coliformgroup.E.coli isthe mostwell-known
coliformbacteriaresponsibleforstomachailmentssuchasdiarrheaandotherinfections.There are four
typesof E. coli classedbysymptomsof infection.EntertoxigenicE.coli causesthe commonlyknown
travellingdiarrheaandsymptomsincludenausea,fever,andwaterydiarrhea.
1.6BACTERIAL GROWTH
Growth of Bacteriais the orderlyincrease of all the chemical constituentsof the bacteria.Multiplication
isthe consequence of growth.Deathof bacteriaisthe irreversiblelossof abilitytoreproduce.Bacteria
are composedof proteins,carbohydrates,lipids,waterandtrace elements.
1.7FACTORS REQUIRED FOR BACTERIAL GROWTH
1.14.1 Environmental Factors affectingGrowth
 Nutrients: Nutrients in growth media must contain all the elements necessary for the
synthesis of new organisms. In general the following must be provided: (a) Hydrogen
donors and acceptors, (b) Carbon source, (c) Nitrogen source, (d) Minerals: sulphur and
phosphorus, (e) Growth factors: amino acids, purines, pyrimidines; vitamins, (f) Trace
elements: Mg, Fe, Mn.
 pH of the medium: Most pathogenic bacteria grow best in pH 7.2-7.4. Vibno cholerae can
grow in pH 8.2-9.0.
 Gaseous Requirement: (a) Role of Oxygen: Bacteria may be classified into four groups
on oxygen requirement:
(i) Aerobes:Theycannotgrowwithoutoxygen,e.g.Mycobacteriumtuberculosis.
(ii) Facultative anaerobes.Thesegrowunderbothaerobicandanaerobicconditions.Mostbacteriaare
facultative anaerobes,e.g.Enterobacteriaceae.
(iii)Anaerobes:Theyonlygrowinabsence of free oxygen,e.g.Clostridium, Bacteroides.
(iv)Microaerophils:growbestinoxygenlessthanthatpresentinthe air,e.g.Campylobacter.
(b) Carbondioxide.AllbacteriarequireCO2fortheirgrowth.Most bacteriaproduce CO2. N.
gonorrhoeae andN.meningitidesandBr abortusgrow betterinpresence of 5 per centCO2.
 Temperature: Most bacteria are mesophilic. Mesophilic bacteria grow best at 30-37°C.
Optimum temperature for growth of common pathogenic bacteria is 37°C. Bacteria of a
species will not grow but may remain alive at a maximum and a minimum temperature.
 Light: Optimum condition for growth is darkness.
 Ionic strength and osmotic pressure: Bacterial growth depends upon Ionic strength and
osmotic pressure.

12. 1.8BATCH CULTURE CURVE OF BACTERIA
The growth of bacteria(or othermicroorganisms,asprotozoa,microalgae oryeasts) inbatchculture can
be modeledwithfourdifferentphases:
 Lag phase
 Log phase or exponential phase
 Stationary phase
 and Death phase or decline phase

Figure 1: Bacteria Growth Curved
1.16.1 Lag Phase: In this phase there is increase in cell size but not multiplication. Time is
required for adaptation (synthesis of new enzymes) to new environment. During this phase
vigorous metabolic activity occurs but cells do not divide. Enzymes and intermediates are
formed and accumulate until they are present in concentration that permits growth to start.
Antibiotics have little effect at this stage.
1.16.2 Exponential Phase or Logarithmic (Log) Phase: The cells multiply at the maximum
rate in this exponential phase, i.e. there is linear relationship between time and logarithm of the
number of cells. Mass increases in an exponential manner. This continues until one of two things
happens: either one or more nutrients in the medium become exhausted, or toxic metabolic
products, accumulate and inhibit growth. Nutrient oxygen becomes limited for aerobic
organisms. In exponential phase, the biomass increases exponentially with respect to time, i.e.
the biomass doubles with each doubling time. The average time required for the population, or
the biomass, to double be known as the generation time or doubling time. Linear plots of

13. exponential growth can be produced by plotting the logarithm of biomass concentration as a
function of time. Importance: Antibiotics act better at this phase.
1.16.3 Stationary Phase: Due to exhaustion of nutrients or accumulation of toxic products death
of bacteria starts and the growth cease completely. The count remains stationary due to balance
between multiplication and death rate. Importance: Production of exotoxins, antibiotics,
metachromatic granules, and spore formation takes place in this phase.
1.16.4 Decline Phase or Death phase: In this phase there is progressive death of cells.
However, some living bacteria use the breakdown products of dead bacteria as nutrient and
remain as persisted. The number of dead cells exceeds the number of live cells. Some organisms
which can resist this condition can survive in the environment by producing endospores.
1.9VIRUS
A virus is a small parasite that cannot reproduce by itself. Once it infects a susceptible cell,
however, a virus can direct the cell machinery to produce more viruses. Most viruses have either
RNA or DNA as their genetic material. The nucleic acid may be single- or double-stranded. The
entire infectious virus particle, called a virion, consists of the nucleic acid and an outer shell of
protein. The simplest viruses contain only enough RNA or DNA to encode four proteins. The
most complex can encode 100 – 200 proteins.
ALGAE
Algae are simple plants that can range from the microscopic (microalgae), to large seaweeds
(macro algae), such as giant kelp more than one hundred feet in length. Microalgae include both
cyanobacteria, (similar to bacteria, and formerly called “blue-green algae”) as well as green,
brown and red algae. Algae cause eutrophication phenomena and useful in oxidation ponds.
PROTOZOA
Protozoa (also protozoan, plural protozoans) is an informal term for single-celled eukaryotic
organisms, either free-living or parasitic, which feed on organic matter such as other
microorganisms or organic tissues and debris. Historically, the protozoa were regarded as "one-
celled animals," because they often possess animal-like behaviors, such as motility and
predation, and lack a cell wall, as found in plants and many algae
SEWAGE TREATMENT
Sewage treatment is the process of removing contaminants from wastewater, primarily from
household sewage. It includes physical, chemical, and biological processes to remove these
contaminants and produce environmentally safe treated wastewater.

14. OBJECTIVES OF SEWAGE TREATMENT
 Removal of micro-organic which may be the cause of dangerous diseases
 Removal of floatable and postponed particles
 To improve the quality of wastewater.
 To make the wastewater usable for agricultural, aquaculture etc.
TYPES OF SEWAGE TREATMENT
Sewage treatment, however, can also be organized or categorized by the nature of the treatment
process operation-
 Physical
 Chemical
 Biological
PHASES of SEWAGE TREATMENT
 Preparatory or Preliminary Treatment
 Primary or Physical Treatment
 Secondary or Biological Treatment
 Tertiary or Advanced Treatment
 Sludge Treatment
 Disinfection
SELF-PURIFICATION IN A RIVER
 Self-purification is the ability of rivers to purify itself of contaminants by natural processes.
It is produced by certain processes which work as rivers move downstream. These
mechanisms can be inform of dilution of polluted water with influx of surface and
groundwater or through certain complex hydrologic, biologic and chemical processes such
as sedimentation (behind obstruction), coagulation, volatilization, precipitation of colloids
and its subsequent settlement at the base of the channel, or lastly due to biological uptake
of pollutants
There are two broad stages of self-purification
 Reversible stage
 Irreversible stage
1.24.1 Reversible stage: The reversible stage of self-purification is the stage at which the natural
processes of a river can easily deal with incoming pollutants within a considerable stretch of the
river.

15. 1.24.2 Irreversible stage: The irreversible stage is when the rate of contamination exceeds the
natural capacity of the river, and thus restoration can practically be achieved by evacuation of
wastes.
FACTORS AFFECTING SELF PURIFICATION
 Dilution
 Current
 Temperature
 Sunlight
 Rate of Oxidation
 Dispersion due to current
 Reduction
Sewage Treatment Process
There are four main stages of treatment in a typical sewage treatment plant, but the design or
layout can vary from site to site. These plants are categorised into one of three types, based on
the method of secondary treatment, i.e. Biological Filter, Activated Sludge, and Pasveer Ditch.

16. Pollutants in sewage
•BOD(Bio Chemical Oxygen demand)
•COD(Chemical Oxygen demand)
•TSS(Total Suspended Solids)
•PH
BOD(BiochemicalOxygendemand)
The BOD is an important measure of water quality .It is measure of the amount of oxygen
needed by bacteria and other organisms to oxidize the organic matter present in a water sample
over a period of 5 days at 20 degree C.
COD (Chemical Oxygen Demand)
COD Measures all organic carbon with the exception of some aeromatics
(BENZENE,TOLUENE,PHENOL etc.) which are not completely oxidized in the reaction.
COD is a chemical oxidation reaction
Ammonia will not be oxidized.
TotalSuspended Solids
Total suspended solids(TSS) include all particles suspended in water which will pass through a
filter.
As levels of TSS increase, a water body begins to lose its ability to support a diversity of aquatic
life.
Suspended solids absorb heat from sunlight, which increases water temperature and
subsequently decreases levels of dissolved oxygen(warmer water holds less oxygen than cooler
water)

17. Components of Sewage Treatment Plants
• Pumping of Sewage
• Primary Treatment
• Secondary treatment
• Tertiary Treatment
Pumping Station
• Receiving Chamber
• Coarse Screening
• Wet Well (Raw Sewage Sump)
• Pump House
• Raw Sewage Pumps

18. SELECTION OF PUMPS FOR RAW SEWAGE
• FOR MAIN PUMPING STATION (MPS) I:S. 5600-2005 NUMBER OF PUMPS REQUIRED
(INCLUDING STANBY)
No. of ½ DWF
2 No. of 1 DWF
1 No. of 3 DWF
• FOR INTERMEDIATE PUMPING STATION (IPS) NUMBER OF PUMPS REQUIRED
(INCLUDING STANBY) FOR CAPACITY OF PUMPING STATION UPTO 3 MLD
1 No. of 1 DWF
1 No. of 2 DWF
1 No. of 3 DWF
NUMBER OF PUMPS REQUIRED (INCLUDING STANBY) FOR CAPACITY OF
PUMPING STATION ABOVE 3 MLD
2 No. of ½ DWF
2 No. of 1 DWF
1 No. of 3 DW
VELOCITY CONSIDERATION IN DESIGN OF PUMPING (RISING)
MAIN FOR PUMPING SEWAGE
• The size of Rising main should be designed after taking into consideration that:
Maximum velocity at peak flow should not exceed 2.7 m/s.
Minimum velocity at low flows should not be less than 1 m/s.

20. 1.Primary Treatment
It is essential to remove large solids, e.g. road grit and silt from the raw sewage in order to
prevent mechanical damage or blockages to pumps, valves, channels, and orifices. The initial
stage of the Primary Treatment includes a settling channel or tank, known as Grit Removal,
followed by screening, to remove floating and large organic material. Coarse screens, generally
bars with 6mm spacing, are followed by fine screens, and then drum filters. Screening may be
combined with maceration, which involves shredding the raw sewage, followed by a process to
crush the solids into very small particles.
The screened sewage is then passed to a further tank, known as Sedimentation, to settle the bulk
of the suspended matter. Colloidal and dissolved solids are not removed and require further
treatment at the Secondary Treatment stage.
 Fine Screening
 Grit Removal
 Primary Clarification
Screening

21.  Objective : Removal of coarse solids
 Types of screens : Fine / medium / coarse
 Cleaning of screens : Manual / mechanical
 Benefits : Protection of pumps
 Coarse Screening : 20mm clear spacing in bars
 Fine screening : 6mm clear spacing in bars

23. Primary Treatment
Grit Removal
Objective : Removal of inorganic solids eg. ebbles/ sand/ Silt to protect moving mechanical
equipment
Principle : Gravity separation (a) effective size 0.15 Primary Treatment mm (b) specific gravity
– 2.65
Types : Manual grit removal - Rectangular channel Mechanical grit removal - Circular tank
Grit removal Mechanism : Screw classifier / reciprocating classifier

25. 2. SecondaryTreatment
Biological Reactions The sewage consists of toxic chemicals both organic or inorganic. Organic
waste, containing carbon, combined with other chemical elements, is broken down by the
biological processes. This involves developing a culture of bacteria and other micro-organisms,
which in the presence of sufficient oxygen, multiplies and feeds on the chemical substances in
the sewage. Oxidation of the ammonia, for example, results in the conversion to nitrogen
compounds, such as nitrite (NO2 – ), and with further oxidation, to nitrate (NO3 – ). This
reaction is termed nitrification. Inorganic chemicals can also be treated, to a lesser extent by
biological action, but they may require some form of chemical treatment. If the process is carried
out correctly, the net result is a treated sewage which has a very low toxicity level, suitable for
final discharge.
The growth of the population of micro-organisms is determined by the availability of nutrient
(provided by the raw sewage), temperature, pH, and (most importantly) dissolved oxygen.
Optimum conditions vary according to the species, but are approximately 25 to 32°C, 5.5 to
9.5pH, and 2mgl-1 respectively

27. Typical biochemical reactions produced by the action of micro-organisms on sewage are
shown in Fig. 3. Both the Biological filter and the Pasveer Ditch systems, tend to be used
on smaller, rural treatment plants. However, activated sludge treatment is employed in
most modern plants throughout the world.
Biological Filtration
This consists of a large circular tank or series of tanks containing stone or plastic pieces which is
sprayed with the screened sewage by a mechanical rotating arm moving over the surface of the
bed. The medium is sufficiently loose to allow the liquid to permeate it and provide free access
of air. A thin film of microorganisms is then supported on the bed which provide biological
decomposition of the sewage. The nature of the medium is critical to ensure an adequate
retention time for maximum efficiency. The liquid leaving the bed passes to further settling or
humus tanks, in which residual solids collect, and are withdrawn periodically for sludge disposal.
Although this system has been in common use since the early 1900s, the disadvantage of the
biological filter is mainly due to difficulties in control with variation in flow and concentration of
the sewage, and its unsuitability for large scale treatment.
Sewage Treatment
Method of Treatment-Aerobic, Anaerobic.

28.  Aerobic- Sewage treatment in the presence of Oxygen-MBBR, SBR-where
aerators/blowers aerators/blowers are installed-generally no smell during treatment.
 Anaerobic- Sewage treatment in the absence of Oxygen-UASB-No aerators/blowers are
required-foul smell during treatment
VARIOUS SEWAGE TREATMENT TECHNOLOGIES
 Activated Sludge Process (ASP)
 Upflow Anaerobic Sludge Blanket Reactor (UASB)
 Moving Bed Biofilm Reactor (MBBR)
 Sequential Batch Reactor (SBR)
 Raw Effluent In
 Aeration
 Sedimentation
 Treated water out
 Sludge Recirculation
 Sludge withdrawl

29. b. Activated Sludge Process (ASP)Technology
The activated sludge method, first instigated in 1914, involves developing a culture of bacteria
and other organisms in a large tank and on lanes containing the settled sewage. Oxygen in the
form of air or pure oxygen is forced into the sewage by mechanical means to sustain the
oxidation process, More sludge is made every day than is actually needed to continue the
process, so the surplus is pumped to the SludgeTreatment stage. The oxygen required for efficient
oxidation is provided by one of two methods:
i. Mechanical Aeration. Agitators are used on the surface of the tanks, the rate of aeration can
be controlled by varying the speed or depth of immersion of the agitator, see Fig 4. In practice,
many parallel lanes are often used with one or more agitators in each lane.

31. ii. Air/Oxygen Diffusion.
Oxidation is achieved using perforated pipes or domes called, diffusers, positioned in the base of
the tanks. Air or pure oxygen from compressors is pumped through these diffusers, producing
small bubbles in the sewage, providing very efficient oxidation – see Fig 5. The rate of oxidation
is then controlled by varying the speed of the compressors.
ASP
• Advantages
 Can sustain seasonal variation
 Less land requirement than UASB
• Disadvantages
 High energy consumption
 Foaming, particularly in winter season, may adversely affect the oxygen transfer, and
hence performance
 Requires elaborate sludge digestion /drying/disposal arrangement
 More land requirement than SBR & MBBR
 Nitrogen and Phosphorous removal requires additional anoxic tank and > 3 times internal
recirculation
ASP

32. a. Pasveer Ditch
This system was developed only in 1953, and it is more widely employed in main land Europe
than in the UK and the rest of the world. Basically, it consists of an oval-shaped channel,
approximately 2 to 3 metres deep, into which sewage is passed after primary treatment. Based on
the same biological processes as in activated sludge, the sewage is aerated and circulated around
the ditch by means of one or more rotors mounted at different points around the ditch The depth
of immersion, and speed of rotation, is adjusted to suit the oxygen demand of the sewage. The
effluent is recirculated until adequate aeration is achieved before being passed to the settling
tank, for tertiary treatment. One variation of the oval Pasveer Ditch design, is an arrangement
where the ditch is constructed as one long channel, often in a zigzag layout to save space. Rotors
are used in the same way to aerate and propel the sewage along the ditch as the biological
process takes place.

33. Aeration/Oxidation control
In the case of the Activated Sludge and Pasveer Ditch, the volumes of air or oxygen required to
treat sewage is large. By measuring the dissolved oxygen in the aeration/ oxidation lanes, careful
control is kept of the volumes produced, limiting the value to around 2mgl-1 in the sewage
sludge. This is just sufficient for the degree of treatment required and ensures that complete
nitrification of the ammonia is achieved – see Fig 6.
3. Tertiary Treatment
Treated sewage from the secondary treatment is then passed for final clarification or
filtration before discharge to the river or sea. The clarifier is a settling tank, similar to that
used for primary treatment, and may be followed by a polishing filter
.

34. 4. Sludge Treatment
The total recovered solids from the grit traps, screens, filters, surplus activated sludge,
and settling tanks are passed periodically to the Sludge Treatment Plant. On older plants
the sludge may be passed to large lakes or lagoons, from which the water is run off or
allowed to evaporate slowly. The remaining solids are buried, burned, or sold as fertiliser.
Current practice involves dewatering of the sludge with filters before being passed on to
digesters. Here, anaerobic micro-organisms flourish in warm conditions, breaking down
any sludge into inorganic solids and methane gas. This gas can be used to provide power
for electricity generation, to use on the site.
Upflow Anaerobic Sludge BlanketReactor(UASB)
 The Up flow Anaerobic Sludge Blanket reactor (UASB) maintains a high
concentration of biomass through formation of highly settleable microbial
aggregates. The sewage flows upwards through a layer of sludge
 .The sludge in the UASB is tested for pH, volatile fatty acids (VFA), alkalinity,
COD and SS. If the pH reduces while VFA increases, the sewage should not be
allowed allowed into the UASB until the pH and VFA stabilise.
 The reactor may need to be emptied completely once in five years, while any
floating material (scum) accumulated inside the gas collector channels may have
to be removed every two years to ensure free flow of gas
 All V-notches must be cleaned in order to maintain the uniform withdrawal of
UASB effluent coming out of each V-notch. The irregular flow from each V-
notch results in the escape of more solids washout. Similarly, blocking of the V-
notches of the effluent gutters will lead to uneven distribution of sewage in the
reactor

37. UASB
Advantages
 Requires less power than aerobic processes
 Biogas generated can be used as fuel or electricity
Disadvantages
 UASB alone does not treat the sewage to desirable limits, therefore downstream aerobic
treatment is compulsory
 Requires very large space due to post treatment
 ecovery of biogas is not sufficient to produce substantial electricity in case of municipal
MOVING BED BIO REACTOR (MBBR) PROCESS
 Moving Bed Bio Reactor (MBBR) process is based on the bio-film of organisims
developed on carrier elements.
 This media is floating in the Aeration tank and kept floating by air from diffusers
which are placed at the bottom of tank.

38.  The process process is intended intended to enhance enhance the activated
activated sludge process process by providing greater biomass in aeration tank
and thus by reducing volume of the tank
 After aeration tank sedimentation tank is provided for settlement of sloughed
biomass
 Clear water clarifier overflows from weir and is further subjected to disinfection.
MBBR

39. Quantity of BIO Media
 Check Design approved by SE to see quantity of BIO media 1m 3 per 7.5 Kg
BOD considering surface area of media 250 m 2/m 3
 The specifications are given in agreement. Specific gravity 0.96.
 Make by Kaldnes biofilm carrier

SEQUENTIAL BATCH REACTOR (SBR) PROCESS
 Sequential Batch Reactor is true batch process where fill, aeration, settle and decant steps
are carried out in sequence of batches in a single basin.
 Screened, de-gritted sewage is fed into the SBR Basins for biological treatment to remove
BOD, COD, Suspended Solids, Biological Nitrogen and Phosphorous.
 SBR process shall work on batch mode in single step.
 It performs biological organic removal, nitrification, de-nitrificatio n and biological
phosphorous removal.

41. SBR Process
SBR / Cyclic Activated Sludge Process
 Better Quality Effluent: 98 % BOD removal efficiency. Sewage can be treated to
reuse/recycle quality of TSS < 10 mg/l, COD < 100 ppm, BOD < 10 ppm, TN <
10 ppm, TP < 2 ppm in a single stage of treatment using Batch process.
 Bio-nutrient removal (BNR) : N & P removal
 Secondary clarifier not required, less foot print area • Flexibility for efficient
removal of BOD, TSS, N& P under all loading conditions.
 Automatically controlled by PLC . Based on process requirement, the aeration
facility is optimized based on DO levels and by varying operating frequency of
the blowers. Less power consumption.

SBR / Cyclic Activated Sludge Process
Advantages
 Controls growth of filamentous bacteria and avoids bulking of sludge.
 Provides stabilised sludge.
 Process with primary clarifier can generate power
 Allows for easy modular expansion for population growth

42. Disadvantages
 Compared to the conventional ASP / MBBR /UASB, a higher level of
sophistication and maintenance is associated due to automation
SBR gives high performance with Nutrient removal
Sludge Handling – Sludge Drying Beds
 Objective : Dewatering of sludge
 Important Features
- Conventional method of sludge drying
- No power requirement
- Substantial area is required
- Difficult to operate in monsoon
- Labour intensive
- Manual scrapping and loading of dried sludge
-

43. Phosphate and Nitrate Reduction
More complex activated sludge plants, precede the aeration/oxidation stage with
phosphate and/or nitrate reduction stages. All three stages are normally carried out in a
series of long partitioned lanes. The sewage flows over or under these partition walls,
from one stage to the next – see Fig 7.
Phosphate reduction is carried out to reduce the levels of phosphate in the final sewage
treated effluent. It is achieved by the addition of Ferric Sulphate – Fe2(SO4)3 to the
sewage, causing the phosphate to coagulate with the ferric. This forms a sludge with can
then be easily settled and passed on to the Sludge Treatment stage .
To provide better control of the aeration stage of the treatment process, some plants
(pioneered in Germany) employ an anaerobic pretreatment stage. One effect of a
pretreatment stage is to reduce the levels of nitrate found in the raw sewage. The
reduction of nitrate provides a means of measuring the anaerobic process, resulting in
effective control. The anaerobic conditions consume the oxygen bound up in the ions
(NO3 – ) releasing nitrogen gas to the atmosphere. Methanol is added to the process to
act as a nutrient to increase bacteria activity
Some treatment plants may carry out nitrate reduction after the aeration/oxidation stage to
reduce the levels of nitrate in the final treated sewage.

44. Instrumentation
Instrumentation on sewage plants is dependent on the size of the plant and the type of control
required. Automatic monitoring and control instrumentation must be used to ensure that the
optimum process conditions are maintained, and its use becomes essential with the introduction
of more stringent controls on discharge into water courses – see Table 1. As well as improving
the control and the final sewage effluent quality from the plant, operating costs can also be
significantly reduced.
As already stated, Dissolved Oxygen monitors are essential to provide optimum control of the
aeration/oxidation stage of the treatment process. Many motors or compressors are used on large
treatment plants which can consume several hundred kW, so by incorporating careful control,
substantial savings in electricity costs can be achieved. Even on small treatment plants,
significant saving can be achieved by careful control.
Ammonia monitors are often installed on the final effluent stream to ensure the discharge limits
have been met and also as an indication of the process efficiency. However, if phosphate or
nitrate reduction is employed, this again requires process monitoring and control.
Suspended Solids monitors are invaluable throughout the plant to indicate load, efficiency and
correct operation of each stage of the process
pH is often used to monitor the raw sewage to guard against acidic or alkaline effluent entering
the plant which could upset, or in severe circumstances, kill the microorganisms used to carry
out biological reaction. pH and conductivity systems could also be employed to monitor
particular treatment processes.
Biological Oxygen Demand (BOD) , which gives an indication of the amount of organic matter
entering the plant, is normally measured in the laboratory, but on-line analysers are becoming
more common