The document discusses the microbiology of wastewater treatment. It describes the types and characteristics of wastewater and indicators used to measure wastewater strength like BOD, COD, and TOD. It outlines the pollution problems caused by untreated wastewater. It then explains the various methods used in wastewater treatment including primary treatment to remove solids, and secondary treatment using processes like septic tanks, Imhoff tanks, trickling filters, activated sludge, and oxidation ponds where microorganisms break down organic matter.

1. Microbiology of Waste Water
D r . M o h a m me d A z i m B a g b a n
A s s t . P r o f e s s o r & H e a d ,
D e p a r t m e n t o f M i c r o b i o l o g y ,
C . U . S H A H I N S T I T U T E O F S C I E N C E
MI 202 Unit-IV

2. Contents
• Type of wastewater, chemical and microbiological characteristics of
wastewater
• BOD, COD and TOD as indicators of strength of wastewater, pollution
problems due to disposal of untreated wastewater.
• Methods of wastewater treatment
• a. Primary treatment and secondary treatment : principles and role of
microorganisms in septic tank, imhoff tank, trickling filters, activated sludge
process, oxidation ponds
• b. Advanced treatment, final or tertiary treatment and efficiency of waste
treatment procedures
• c. Solid waste processing : anaerobic sludge digestion and composting

3. Type of wastewater, chemical and microbiological characteristics of wastewater
• Waste water is the used water effluent of a community, industry,
agriculture, etc. Following are the three types of waste waters :
• (1) Domestic wastewater
• (2) Industrial wasteswater
• (3) Ground, surface and atmospheric waters.

4. Type of wastewater, chemical and microbiological characteristics of wastewater
• 1 Domestic waterborne wastes or sewage, including human excrement and wash waters-everything that
goes down the drains of a home and into a sewerage system
• 2 Industrial waterborne wastes such as acids, oil, greases, and animal and vegetable matter discharged
by factories
• 3 Ground, surface, and atmospheric waters that enter the sewerage system.
• The wastewater of a city is collected through a sewerage system, which carries the used water to its
ultimate point of treatment and disposal. There are three kinds of sewerage systems: (1) sanitary sewers,
which carry domestic and industrial wastewater: (2) storm sewers, designed to carry off surface and
storm (atmospheric) water; and (3) combined sewers, which carry all the wastewater (sewage) through a
single system of sewers.

5. Type of wastewater, chemical and microbiological characteristics of wastewater
• Chemical Characteristics:
• Domestic wastewater or sewage consists of approximately 99.9 percent water. 0.02 to 0.03 percent
suspended solids, and other soluble organic and inorganic substances. On a percentage basis, the
amount of solids appears small; however, the tremendous volume of material handled daily by a major
municipal plant (e.g., several hundred millions of gallons) contains as much as 100 tons of solids. The
chemical constituents, present in low concentrations, nevertheless are extremely important and are
subject to variations between communities as well as within a community, even from hour to hour.
Inorganic chemicals initially present in the water supply will likewise be present in the sewage organic
compounds are contributed through human excrement and other domestic wastes, and both organic and
inorganic compounds are added by industrial wastes.

6. Type of wastewater, chemical and microbiological characteristics of wastewater
• Chemical Characteristics:
• For example, sugar factories, paper mills, and creameries add organic substances, mines and
metal industries contribute acid and salts of metals and other inorganic wastes. The organic
compounds in sewage are classified as nitrogenous or non-nitrogenous. The principal
nitrogenous compounds are urea, proteins, amines, and amino acids; the non nitrogenous
substances include carbohydrates, fats. and soaps.
• Modern technology may produce significant changes in sewage characters tics. The increased use
of household garbage-disposal units has increased the total organic load. Some synthetic
detergents displacing soaps are resistant to microbial degradation.

7. Type of wastewater, chemical and microbiological characteristics of wastewater
• Microbial Characteristics:
• Fungi, protozoa, algae, bacteria and viruses may be present.
• Raw sewage may contain millions of bacteria per ml, including the coliforms, streptococci, anaerobic spore
forming bacilli, the Proteus group and other types originating in the intestinal tract of humans.
• Sewage is also a potential source of pathogenic protozoa and viruses.
• Predominant physiological types of bacteria may shift during the course of sewage digestion.
• In an anaerobic digester, aerobic and facultative anaerobic types (Enterobacter, Alcaligenes, Escherichia,
Pseudomonas, etc.) predominate during initial stages. This is followed by methane producers, which are strict
anaerobes, e.g. Methanobacterium, Methanosarcina and Methanococcus.
• Organic acids produced by the facultative anaerobic bacteria are metabolized by the methane formers and the end
products produced are methane and CO2: Large amount of these gases are produced in anaerobic digesters..

8. BOD, COD and TOD as indicators of strength of wastewater
Lab
Methods
BOD
COD
TOCTOD
ThOD

9. • Biochemical Oxygen Demand (BOD)
• The most widely used parameter to determine organic pollution of both wastewater and surface water is
the 5- day BOD (BOD).
• This determination involves the measurement of the dissolved oxygen used by microorganisms in the
biochemical oxidation of organic matter in 5 days.
• To ensure that meaningful results are obtained, the sample must be suitably diluted with aerated, nutrient
- containing dilution water. The dilution water is 'seeded' with bacterial culture, if necessary, to degrade
the organic matter present in the waste water. It is ensured that carbon will become a limiting factor while
the supply of oxygen and nutrients will be in surplus throughout the test.
• The incubation period is usually 5 days at 20°C, but other length of time and temperature can be used. The
temperature should be constant throughout the test.

11. • Biochemical Oxygen Demand (BOD)
• After incubation, the dissolved oxygen (DO) of the sample is measured with a
membrane electrode or by the Wrinkler's method and BOD is calculated.
• BOD values commonly found in different waste water:
Type BOD (mg/L)
Domestic sewage (raw) 110-400
Domestic sewage (treated) 10
Dairy waster water 900
Tannery waste water 1200
Textile dyeing waste water (raw) 600-700

12. • Chemical Oxygen Demand (COD)
• The COD test is used to measure the content of organic matter of both wastewater and natural
waters. The oxygen equivalent to the organic matter that can be oxidized is measured by using a
strong chemical oxidizing agent such as potassium permanganate in an acidic medium.
• The test must be performed at an elevated temperature. A catalyst (silver sulpate) is required to aid
the oxidation of certain classes of organic compounds. The COD test is also used to measure the
organic matter in industrial and municipal wastes that contain compounds that are toxic to
biological life.
• The COD of a waste is in generally, higher than the BOD because more compounds can be
chemically oxidized than by biological means. The COD of domestic sewage is generally in the
range250 - 1000 (mg/l).

13. • Total Oxygen Demand (TOD)
• In this test, organic substances and to a minor extent, inorganic substances are
converted to stable end products in a platinum - catalyzed combustion chamber.
• The TOD is determined by monitoring the oxygen content present in the nitrogen
carrier gas. This test can be carried out rapidly, and the results can be correlated
with the COD.

14. • Total Organic Carbon (TOC)
• Total Organic Carbon (TOC) is a measure of all forms of carbon present, whether it
is utilized by microorganisms or not.
• It is determined by oxidizing the organic matter at high temperature in an oxygen
stream and measuring the CO2 produced by infrared or potentiometric techniques.

15. • Theoretical Oxygen Demand (ThOD)
• Theoretical oxygen demand (ThOD) is the calculated amount of oxygen required to
oxidize a compound to its final oxidation products. However, there are some
differences between standard methods that can influence the results obtained: for
example, some calculations assume that nitrogen released from organic
compounds is generated as ammonia, whereas others allow for ammonia oxidation
to nitrate. Therefore, in expressing results, the calculation assumptions should
always be stated.

16. Pollution problems due to disposal of untreated wastewater
• Sewage is the term used for wastewater that often contains faeces, urine and
laundry waste.
• There are billions of people on Earth, so treating sewage is a big priority.
• Sewage disposal is a major problem in developing countries as many people in
these areas don’t have access to sanitary conditions and clean water.
• Untreated sewage water in such areas can contaminate the environment and
cause diseases such as diarrhoea.

17. Pollution problems due to disposal of untreated wastewater
• Sewage in developed countries is carried away from the home quickly and hygienically
through sewage pipes.
• Sewage is treated in water treatment plants and the waste is often disposed into the
sea.
• Sewage is mainly biodegradable and most of it is broken down in the environment.
• In developed countries, sewage often causes problems when people flush chemical and
pharmaceutical substances down the toilet. When people are ill, sewage often carries
harmful viruses and bacteria into the environment causing health problems.

18. Wastewater Treatment
• Municipal wastewater treatment is basically applicable to those wastewater which has
been collected from various residential localities through the sewage system of a city and
town, and is treated before being dispersed in open field.
• Municipal wastewater treatment plants carryout a series of treatment processes which
may be summarized as follows:
• Primary treatment
• Secondary treatment
• Advanced treatment
• Final treatment

19. Wastewater Treatment

20. Wastewater Treatment
• Primary treatment:
• This is also known as physical treatment. It consists of methods to remove solid
materials and these methods are basically mechanical.
Primary
Treatment
Screening
Grinding
Floatation
Sedime
ntation

21. Primary Treatment
Screening:
In this method, the wastewater
collected from various residential
areas is passed through various
sizes of screens such as bar rock,
fine screens and microscreens. The
solid objects which are larger than
the screens will be retained back.
Grinding:
Here, the solid mass is ground or
broken down into smaller particles,
which will settle down in grit
chambers.
Floatation:
Certain substances which are light
in weight and floats on the surface
such as finely divided suspended
solids, particles with densities close
to that of water, oil and gases are
removed by dissolved or induced air
floatation.
Sedimentation:
Sedimentation units such as tanks,
basins or mechanical device provide
the means for concentrating and
collecting the particulate material
referred to as sludge.

22. Wastewater Treatment
• Secondary treatment:
• Secondary treatment processes accomplish oxidation of the organic material in the liquid
waste by microbial activity. During this process microorganisms transform organic
compounds into simple compounds.
Secondary
Treatment
Septic
tank
Imhoff
tank
Trickling
Filter
Activated
Sludge
Process

23. Secondary Treatment
• (A) Septic Tank:
• A septic tank is a sewage - settling tank designed to
retain the solids of the sewage entering the tank long
enough to permit adequate decomposition of the
sludge. Thus, the unit accomplishes two processes.
• (1) Sedimentation, and
• (2) Biological degradation of the sludge.

24. Secondary Treatment
• (A) Septic Tank:
• As sewage enters this type of tank, sedimentation occurs from the upper portion,
permitting a liquid with fewer suspended solids to be discharged from the tank.
• The sediment solids are subjected to degradation by anaerobic bacteria, hence the end
products are still unstable i.e. high in BOD and odorous.
• When microbial growth is completed, it forms a stable settle structure called flocs.
• Septic tank is the most satisfactory method for disposing of sewage from small
installations, especially individual dwellings and isolated rural buildings where public
sewers are not available. They cannot however, be relied upon to eliminate pathogenic
microorganisms carried in the sewage.

25. Secondary Treatment
• (B) Imhoff Tank:
• The Imhoff tank was developed to correct the two main defects
of the septic tank. It prevents the solids once removed from the
sewage from being mixed with it again, but still provides for the
decomposition of these solids in the same unit.
• It provides an effluent amenable to further treatment. The
Imhoff tank may be either circular or rectangular and is divided
into three compartments :
• (i) The upper section or sedimentation compartment.
• (ii) The lower section known as the digestion compartment.
• (iii) The gas vents and scum section.

26. Secondary Treatment
• (B) Imhoff Tank:
• It is desirable to be able to reverse the direction of flow to prevent excessive deposition of
solids at one end of the sediment compartment. Periodically reversing the flow will result in
an even accumulation of sludge across the bottom of the tank.
• In operation, all of the wastewater flows through the upper compartment.
• Solids settle to the bottom of this sloped compartment, slide down and pass through an
opening or slot to the digestion compartment. One of the bottom slopes extends at least 6
inches beyond the slot. This forms a trap to prevent gas or digesting sludge particles in the
lower section from entering the waste stream in the upper section.
• The gas and any rising sludge particles are diverted to gas vents and scum section.

27. Secondary Treatment
• (C) Trickling Filter:
• The trickling filter consists of a bed of crushed stone, gravel, Slage or synthetic material with drains at the
bottom of the tank. Trickling filters have a depth of 5 to 10 feet. The circular round of the trickling filter is
filled with various sizes of stones. In the center of trickling filter, there is an arm running on entire bed.

28. Secondary Treatment
• (C) Trickling Filter:
• The liquid sewage is sprayed over the surface of the bed either by a rotating arm or through nozzles.
• The spraying saturates the liquid with oxygen. The treatment in trickling filter is an aerobic process.
• Wastewater is kept on the bed of stones, stones are of different shapes so the air arrangement of stones
varies.
• The sewage trickles from these air pockets. Now the rotating arm is rotated and begins a new entire cycle.
• The time is noted for the sewage to pass through the bed. Sewage contains bacteria, that adheres on the
stones. The sewage which falls on stones is rich in nutrition, organic compounds and air is sufficient in this
system. Now the air pockets will totally be aerobic and microorganisms will grow, consume the oxygen as
well as nutrients. Then microorganisms multiply slowly. This results information of film of microorganisms
called zoogloeal film.

29. Secondary Treatment
• (D) Activated Sludge Process:
• The activated sludge process is an aerobic suspension type of liquid waste treatment system,
also known as aeration tank digestion. After primary treatment, the sewage containing
dissolved organic compounds is introduced into an aeration tank and mixed with a slurry rich
in bacteria which is called an activated sludge. Air injection and or mechanical stirring
provides the aeration.

30. Secondary Treatment
• (D) Activated Sludge Process:
• The heterogenous nature of the organic substrates in the sewage allows the development of
diverse heterotrophic bacterial populations including gram-negative rods, and other large
filamentous bacteria. and low numbers of filamentous fungi, yeasts and protozoa, mainly
ciliates. The protozoa are important predators of the bacteria along with rotifers.
• The process takes advantage of aerobic micro-organisms that can digest organic matter in
sewage, and clump together (by flocculation) as they do so. It thereby produces a liquid that is
relatively free from suspended solids and organic material, and flocculated particles that will
readily settle out and can be removed.

31. Secondary Treatment
• (D) Activated Sludge Process:
• The general arrangement of an activated sludge process for removing carbonaceous pollution
includes the following items:
• Aeration tank where air (or oxygen) is injected in the mixed liquor.
• Settling tank (usually referred to as "final clarifier" or "secondary settling tank") to allow the biological
flocs (the sludge blanket) to settle, thus separating the biological sludge from the clear treated water.
A portion of the settled sewage sludge is recycled for use as the inoculum for the incoming raw sewage.
The organisms present in the flocs reduces the time for treatment everytime it is recycled.
During the treatment, BOD level is reduced by 85-90%.

32. Secondary Treatment
• (E) Oxidation Ponds:
• Oxidation ponds are also called Lagoons or stabilization ponds. This pond is natural or
artificial. It is basically shallow pond and having a large surface area and depth of 2 to 4 feet.
• In an oxidation pond, wastes are added at single point, either in the middle of the pond or at
the edge of the pond and effluent is removed at the single point at the edge of the pond

33. Secondary Treatment
• (E) Oxidation Ponds:
• An oxidation pond is an aerobic system for the simple secondary treatment of the waste water
in small industrial units or villages. However, the pond is having both aerobic as well as
anaerobic zones. Within an oxidation pond, heterotrophic bacteria degrade organic matter in
the sewage, which results in production of cellular material, CO2 and minerals.
• The production of these substances supports the growth of algae in the oxidation ponds. The
production of this oxygen by photosynthetic activityof algae replenishes the oxygen used by
the heterotrophic bacteria. The performance of oxidation pond is strongly influenced by
seasonal temperature.

34. Advanced Treatment
• The advanced treatment is needed when the organic matter in sewage which has passed
through primary and secondary treatment is not yet completely degraded.
• Various kinds of advanced treatments are there which depends on the type of incoming
sewage. Unit processes have been developed to remove nutrients, simple organic substances
and complex synthetic organic compounds. Processes include biological as well as physico-
chemical methods. Examples are, Biological nitrification denitrification, filtration, reverse
osmosis, carbon adsorption, chemical addition and ion-exchange, etc.
• Includes 2 types:
• Biodisc system or rotating biological contactor
• Modified or non-conventional activated process

35. Advanced Treatment
• Biodisc system or rotating biological contactor is an example of a more advanced type of
aerobic film-flow treatment system. In this process closed packed plastic discs, partially
submerged in a trough containing the sewage are rotated.

36. Advanced Treatment
• Modified or non-conventional activated process is employed for removal of
nitrogen and phosphorus, which are generally removed during tertiary treatment.
• A single sludge system comprising of a series of aerobic and anaerobic tanks is one
method, in which methanol or settled sewage is used as the carbon source by denitrifiers.
• In multisludge system three separate systems are involved in carbonaceous oxidation,
nitrification and denitrification.
• Bardenpho process removes nitrogen as well as phosphorus during nitrification-
denitrification process. It consists of two aerobic and two anoxic tanks followed by a
sludge settling tank.

37. Final Treatment (Tertiary Treatment)
• After final treatment, the water is to be released in water bodies which is to be used by living
creatures.
• Disinfection is commonly accomplished by chlorination. However, current research has
proved the serious impact chlorinated waters have on the aquatic life of the receiving water.
• This has led to the development of several disinfection alternatives. The use of ozone and
ultra-violet light is becoming more prevalent. Many facilities that continue to employ chlorine
for disinfection now include dechlorination prior to discharge into a water body. Dissolved
oxygen may also be added to the treated wastewater prior to final discharge. This process is
termed post aeration that is accomplished by mechanical means or a cascading slow
techniques, which minimizes the decrease in dissolved oxygen of the receiving water bodies.

38. Final Treatment (Tertiary Treatment)
• Activated carbon filters are normally used for the removal of P and N from secondary treated
effluents.
• Phosphate is removed by precipitation as calcium, aluminium or iron phosphate.
• Ammonia (NH3) is removed by Break-point chlorination process, in which it is converted to form
dichloramine and then to molecular nitrogen.
• Nitrogen can also be removed by denitrification.
• Anammox process is an anaerobic nitrogen removal process in which ammonium ion (used as the
electron donor) is allowed to react with nitrite (the electron aceptor) produced due to partial
nitrification. It can convert about 80% of the ammonium ion initially present to nitrogen gas. Tertiary
treatment processes are expensive and hence used only where it is justified.

39. Final Treatment (Tertiary Treatment)
• Removal of pathogens:
• Pathogens present in raw sewage are successfully removed mainly during the activated sludge
process.
• It removes viruses, enteric bacterial pathogens (e.g., Salmonella spp.), Giardia and
Cryptosporidium.
• Chlorination, ozonation and U.V. rays are employed during tertiary treatment process for
killing pathogens.

40. Solid waste processing:
• A major cost at modern large scale wastewater treatment is associated with additional
processing of effluent after tertiary treatment. Solid waste or sludge processing, removal of
pathogens, composting, land-farming, etc. are involved in this activity.
Solid Waste
Processing
Anaerobic
Sludge
Digestion
Thickening
Digestion
Composting
Windrow
Method
Static pile
method

41. Anaerobic Sludge Digestion
• The primary sludge contains about 3.8% solids, where as secondary sludge contains 0.5 to
2.0% solids.
• The steps involved in treatment of sludge includes:
• Thickening: reduction in its volume, by settling in a tank or by centrifugation.
• Digestion: this is for stabilization of the organic matter by microbial activities. It also causes destruction
of pathogens due to higher temperatures reached during the process.
• It is carried out by both anaerobic or aerobic digestion.
• The sludge which accumulates during various treatment stages is collected and pumped into a
separate tank designed for its digestion under controlled conditions. Initially, for a few hours,
air is supplied for aerobic degradation. Aerobic microorganisms degrade the sludge reducing
the solids content, and create anaerobic condition.

42. Anaerobic Sludge Digestion
• Anaerobic digestion takes place for a period of 2-3 weeks in a large covered tank, it results in
the formation of gases namely, methane (60-70%), CO2 (20 - 30%), small amounts of
hydrogen and nitrogen. Methane produced is used as a biofuel (biogas).
• Ripe sludge which contains an actively growing population of diverse microorganisms is used
to seed fresh sludge collected in tanks. Digestion is allowed in controlled conditions.
• Finally, air drying, centrifugation or vacuum filtration are employed for dewatering the
solids, to decrease its volume and reduce transportation cost.
• Land farming is a practice for disposal of biosolids produced during wastewater treatment
onto agricultural land. Processes for reduction of pathogens are used to treat sludge before
adding to soil. The biosolids may be liquid or solid in nature for soil application. It adds water
and nutrients to soil that promotes soil fertility and plant growth.

43. Composting
• Composting is a process for biodegradation or decomposing organic solid waste by aerobic,
Mesophilic and Thermophilic Microorganisms. Dewatered sludge or solid organic wastes after
removal of inorganic fraction is ground, mixed with sludge or bulking agents such as wood
chips, shredded newspaper, resins, etc. and composted. Microbial degradation activities
converts the waste into a stable humus like product.
• In Windrow method the solid waste is piled up in long rows, covered and allowed to
decompose. The material is turned over at regular intervals.

44. Composting
• The Static pile or Aerated pile method waste is piled up on perforated pipes through
which air is pumped. This speeds up the composting process. At some modern facilities, an
enclosed reactor composting under controlled conditions is carried out in an industrial
bioreactor or fermenter. The composting occurs in 2-4 days, however, it is expensive.
Windrow method Static Pile method

45. Composting
• For optimal composting the C:N ratio must be 40:1, temperature 50 - 60°C, and moisture 50-
60%.
• Mesophilic bacteria and fungi grow first followed by Thermophilic organisms such as
Thermomonospora spp., Clostridium spp., Aspergillus fumigatus, Geotrichum spp., Torula
thermophila, etc.
• The high temperature kills most of the enteric pathogens present during composting of solid
waste. The composted waste is screened for removal and recycling of wood chips, resins, etc.
and humus - like material is used as a soil conditioner as a commercial product, especially for
organic farming.

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