ChapterPDF Available
Dhaka University of Engineering & Technology
(DUET), Gazipur.
HANDOUT ON
INTRODUCTION TO SEWAGE TREATMENT
By
Asaduzzaman
ID: 16201009-P
Department of Civil Engineering
DUET, Gazipur
1.1 INTRODDUCTION
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.
1.2 SEWAGE
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 ow 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 of sewers 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 also be detected in
sewage. With urban runo! come potentially toxic compounds like oil from
cars and pesticides that may reach the treatment plant and, eventually, a
water body.
1.3 COMPOSITION OF SEWAGE
1.4 CLASSIFICATION OF SEWAGE
Sewage may be classified mainly into three types, namely, domestic sewage, industrial sewage,
and storm sewage.
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.
Sewage
Water
(99.9)
Solids
(0.01)
Organic
(70)
Proteins
(65)
Carbohydrate
(25) Fats (10)
Inorganic
(30)
Grit Metals
1.5 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.
1.6 WASTEWATER CHARACTERISTICS
Wastewater is characterized in terms of its:
Physical
Chemical
Biological
1.6.1 Physical Characteristics of Wastewater
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
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 103 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.
1.6.2 Chemical Characteristics of Wastewater
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).
1.6.3 Biological Characteristics of Wastewater
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.
1.7 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
1.8 STRENGTH OF SEWAGE
Contaminants Unit
Concentration
Weak Medium Strong
Total solids (TS) mg/l 350 720 1200
Total dissolved solids (TDS) mg/l 250 500 850
Fixed mg/l 145 300 525
Volatile mg/l 105 200 325
Suspended solids mg/l 100 220 350
Fixed mg/l 20 55 75
Volatile mg/l 80 165 275
Settleable solids mg/l 5 10 20
BOD5, 20oc mg/l 110 220 400
TOC mg/l 80 160 290
COD mg/l 250 500 1000
Nitrogen (total as N) mg/l 204 40 85
Organic mg/l 81 153 35
Free ammonia mg/l 12 25 50
Nitrites mg/l 0 0 0
Nitrates mg/l 0 0 0
Phosphorus (total as P) mg/l 4 8 15
Organic mg/l 13 3 5
Inorganic mg/l 3 5 10
Chlorides mg/l 30 50 100
Sulfate mg/l 20 30 50
Alkalinity (as CaCO3) mg/l 50 100 200
Grease mg/l 50 100 150
Total coliforms No/100 ml 106 - 107107- 108107- 109
Volatile organic compounds µg/l < 100 100 - 400 > 400
Source: Adapted from Metcalf and Eddy Inc., Wastewater Engineering, 3rd edition.
1.9 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)
1.9.1 Theoretical Oxygen Demand
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 1.07300 = 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.
1.9.2 Chemical Oxygen 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
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.
1.9.3 Biochemical oxygen demand (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.
1.9.3.1 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
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)
1.10 DEFINITION 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.
1.11 BRANCHES OF MICROBIOLOGY
Microbiology can be classified into
Pure microbiology
Applied microbiology
1.11.1 Pure microbiology
Bacteriology (Study of bacteria)
Mycology (Study of fungi)
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
1.12 MICROBES 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.
1.13 BACTERIA
Bacteria is a single celled organism which can be found on most materials and surfaces and exist
as single cell, in pair, chains or cluster. They are very small in size and need a microscope to see.
They are unicellular organisms, some are free-living organisms and some are parasitic. Free-
living bacteria use flagella for movement and some are toxins. They are prokaryotic organism i.e.
their nucleuses are not bounded by membrane.
1.13.1 Shapes of Bacteria
Most bacterial species are either spherical, called cocci (sing. coccus, from Greek kókkos, grain,
seed), or rod-shaped, called bacilli (sing. bacillus, from Latin baculus, stick). Some bacteria,
called vibrio, are shaped like slightly curved rods or comma-shaped; others can be spiral-shaped,
called spirilla, or tightly coiled, called spirochaetes.
1.13.2 Type of Bacteria
1.13.2.1 Based on Environment
Various bacteria thrive in varied environment. While some species can withstand extreme
conditions, others need specific moderate conditions to survive. Based on the preference of
environmental conditions for their habitat, bacteria are classified into:
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 Requirement of Oxygen
Bacteria are also classified based on the requirement of oxygen for their survival.
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 (Staining Methods)
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
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 bacteria form endospores, which are extremely tough and impenetrable outer shells, when
exposed to unfavorable conditions. These endospores enable the bacteria to survive these
conditions by remaining in a dormant state. When the conditions are favorable, the bacteria again
revert to their original state. Endospores can help bacteria survive for millions of years in a
dormant state.
Based on whether bacteria form endospores or not, they are classified into the following two
types.
Endospore forming bacteria
Non-endospore forming bacteria.
1.13.3 Coliform Bacteria
Coliform bacteria are defined as rod-shaped Gram-negative non-spore forming and motile or
non-motile bacteria which can ferment lactose with the production of acid and gas when
incubated at 35–37°C. They are a commonly used indicator of sanitary quality of foods and
water. Coliforms can be found in the aquatic environment, in soil and on vegetation; they are
universally present in large numbers in the feces of warm-blooded animals. While coliforms
themselves are not normally causes of serious illness, they are easy to culture, and their presence
is used to indicate that other pathogenic organisms of fecal origin may be present. Such
pathogens include disease-causing bacteria, viruses, or protozoa and many multicellular
parasites. Coliform procedures are performed in aerobic respiration aerobic or anaerobic
conditions.
1.13.4 Types of Coliform Bacteria
There are three types of coliform bacteria
Total coliform bacteria
Fecal coliform bacteria
Escherichia coli or E. coli bacteria
1.13.4.1 Total Coliform Bacteria
Total coliforms include bacteria that are found in the soil, in water that has been influenced by
surface water, and in human or animal waste.
1.13.4.2 Fecal Coliform Bacteria
Fecal coliforms are the group of the total coliforms that are considered to be present specifically
in the gut and feces of warm-blooded animals. Because the origins of fecal coliforms are more
specific than the origins of the more general total coliform group of bacteria, fecal coliforms are
considered a more accurate indication of animal or human waste than the total coliforms.
1.13.4.3 E. Coli Bacteria
Escherichia coli (E. coli) are the major species in the fecal coliform group. E. coli is the most
well-known coliform bacteria responsible for stomach ailments such as diarrhea and other
infections. There are four types of E. coli classed by symptoms of infection. Enter toxigenic E.
coli causes the commonly known travelling diarrhea and symptoms include nausea, fever, and
watery diarrhea.
1.14 BACTERIAL GROWTH
Growth of Bacteria is the orderly increase of all the chemical constituents of the bacteria.
Multiplication is the consequence of growth. Death of bacteria is the irreversible loss of ability to
reproduce. Bacteria are composed of proteins, carbohydrates, lipids, water and trace elements.
1.15 FACTORS REQUIRED FOR BACTERIAL GROWTH
1.14.1 Environmental Factors affecting Growth
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: They cannot grow without oxygen, e.g. Mycobacterium tuberculosis.
(ii) Facultative anaerobes. These grow under both aerobic and anaerobic conditions. Most
bacteria are facultative anaerobes, e.g. Enterobacteriaceae.
(iii)Anaerobes: They only grow in absence of free oxygen, e.g. Clostridium, Bacteroides.
(iv)Microaerophils: grow best in oxygen less than that present in the air, e.g. Campylobacter.
(b) Carbon dioxide. All bacteria require CO2 for their growth. Most bacteria produce CO2. N.
gonorrhoeae and N. meningitides and Br abortus grow better in presence of 5 per cent CO2.
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.
1.16 BATCH CULTURE CURVE OF BACTERIA
The growth of bacteria (or other microorganisms, as protozoa, microalgae or yeasts) in batch
culture can be modeled with four different phases:
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
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.
1.17 VIRUS
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.   
1.18 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.
1.19 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.
1.20 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.
1.21 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.
1.22 TYPES OF SEWAGE TREATMENT
Sewage treatment, however, can also be organized or categorized by the nature of the treatment
process operation-
Physical
Chemical
Biological
1.23 PHASES of SEWAGE TREATMENT
Preparatory or Preliminary Treatment
Primary or Physical Treatment
Secondary or Biological Treatment
Tertiary or Advanced Treatment
Sludge Treatment
Disinfection
1.24 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.
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.
1.25 FACTORS AFFECTING SELF PURIFICATION
Dilution
Current
Temperature
Sunlight
Rate of Oxidation
Dispersion due to current
Reduction
MCQ:
1. What is the percentage of solids in Sewage?
(a) 99.9 (b) 0.01 (c) 1 (d) 0.1
2. Which are not physical characteristics of wastewater?
(a) Color (b) Turbidity (c) pH (d) Temperature
3. Which are chemical characteristics of wastewater?
(a) Odor (b) Solids (c) pH (d) Temperature
4. Which is not one of the three main shapes of bacteria?
(a) Coccus (b) Bacillus (c) Spiral (d) Star
5. Which one is not affecting in self-purification on river?
(a) Dilution (b) Color (c) Sunlight (d) Temperature
Short Question:
1. Why need to treat wastewater?
2. What are the classifications of sewage?
3. What are BOD and COD?
4. Which factors are required for bacteria growth?
5. What are the phases of sewage treatment?
Broad Question:
1. What is sewage? Write the composition of sewage.
2. Briefly describe about wastewater characteristics.
3. What is oxygen demand? Distinguish between BOD and COD.
4. Briefly describe about batch culture growth of bacteria.
5. Describe about self-purification in a river. What is the factors affecting self-purification
in river.
ResearchGate has not been able to resolve any citations for this publication.
ResearchGate has not been able to resolve any references for this publication.