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Home , Water aeration, Water purification

M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

Sewage Treatment and Purification:

Wastewater treatment, also called treatment, the removal of impurities from wastewater, or sewage, before they reach or natural bodies of water such as , , , and oceans. Water (/) is said to be polluted when it contains enough impurities, mainly from human activity, to make it unfit for a particular use, such as drinking, swimming, or fishing. General types of water pollutants include pathogenic organisms, -demanding wastes, plant nutrients, synthetic organic chemicals, inorganic chemicals, microplastics, sediments, radioactive substances etc.

Chemical and Microbiological Characteristics of Waste Water

There are three types of wastewater, or sewage: domestic sewage, industrial sewage, and storm sewage. Domestic sewage carries used water from houses and apartments; it is also called sanitary sewage. Industrial sewage is used water from manufacturing or chemical processes. Storm sewage, or storm water, is runoff from precipitation that is collected in a system of pipes or open channels.

Sewage (mainly industrial) contains a high amount of putrescible , indicated by Bological Oxygen Demand (BOD). Industrial sewage also contains high level of . The volume of produced in a treatment plant is directly related to the total suspended solids present in the sewage. Domestic sewage contains compounds of nitrogen and phosphorus, two elements that are basic nutrients essential for the growth of plants. In lakes, excessive amounts of and can cause the rapid growth of . Algal blooms, often caused by sewage discharges, accelerate the natural aging of lakes in a process called eutrophication.

Table: Gross chemical composition of sewage water (Sophonsiri and Morgenroth, 2004)

1 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

Domestic sewage contains many millions of per gallon, mostly pathogenic while some are beneficial in sewage purification. Coliform from the human intestinal tract are used as indicators of sewage (a high coliform count usually indicates recent sewage pollution). Fungal cells are also found in plants but their numbers are usually low with no single characteristic species routinely detected. Where present, they are often found as an external biofilm of flocs. like amoeba, flagellates and ciliates are also found in sewage. Pathogenic or potentially pathogenic microorganisms (bacteria, , and parasites including protozoa, worms, and rotifers) present in sewage pose a threat to . Major water borne viral diseases include Hepatitis A, polio, Rotaviral diseases etc and protozoan diseases include and infections.

Table: Major pathogenic diseases caused by bacteria present in sewage

Treatment Process

The degree to which wastewater must be treated varies, depending on local environmental conditions and governmental standards. standards include dissolved oxygen, coliforms, , acidity, and toxic substances. There are three levels of wastewater treatment: primary, secondary, and tertiary (or advanced). Primary treatment removes about 60 percent of total suspended solids and about 35 percent of BOD; dissolved impurities are not removed. It is usually used as a first step before secondary treatment. Secondary treatment removes more than 85 percent of both suspended solids and BOD. A minimum level of secondary treatment is usually required in the and other developed countries. When more than 85 percent of total solids and BOD must be removed, or when dissolved and levels must be reduced, tertiary treatment methods are used. Tertiary processes can remove more than 99 percent of all the impurities from sewage, producing an effluent of almost drinking-water quality. Tertiary treatment can be very expensive, often doubling the cost of secondary treatment. It is used only under special circumstances. For all levels of wastewater treatment, the last step prior to discharge of the sewage effluent into a body of surface water is disinfection, which destroys any remaining in the effluent and protects public health. Disinfection is usually accomplished by mixing the effluent with gas or with liquid solutions of hypochlorite chemicals in a contact tank for at least 15 minutes. Because chlorine

2 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

residuals in the effluent may have adverse effects on aquatic life, an additional chemical may be added to dechlorinate the effluent. radiation, which can disinfect without leaving any residual in the effluent, is becoming more competitive with chlorine as a wastewater .

Objective of waste :-

 There are several objective:- . Reduction of the organic content of wastewater. . Removal /reduction of trace organics that are recalcitrant to biodegradation & may be toxic or carcinogenic. . Removal/ reduction of toxic metals . Removal /reduction of nutrients (N,P) to reduce pollution of surface water . Removal or inactivation of pathogenic & parasites.

Major contaminants in waste water:

• Suspended solids • Biodegradable organics • Pathogens & parasites • nutrients • Priority pollutants • Refractory organics • • Dissolved inorganics

Quality indicators:-

• Indicators Biological Oxygen demand:- dissolved oxygen consumed by micro organism for biochemical oxidation Carbonaceous oxygen demand:- amount of oxygen used by a mixed population of heterotrophic microorganism to oxidize organic compounds

Nitrogenous oxygen demand:- Autotrophic bacteria such as nitrifying bacteria also require oxygen to oxidize NH4+ to nitrate, oxygen demand exerted by nitrifies is called NOD

• Chemical oxygen demand:- amount of oxygen necessary to oxidize the organic completely to CO2, H2O & . • :- total organic carbon presents in a given sample,

3 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

Types of water treatment:-

 Liquid waste treatment means, remove pollutants from domestic and industrial waste, so that it is safe to . ▪ Process based on attached microbial growth(trickling Filters). ▪ process ▪ Oxidation of

Oxidation ponds:-  Treatment of waste water in ponds or oxidation of ponds is probably the most important & ancient means of waste water treatment.

 It is also called stabilization ponds or .

Biology of oxidation

 Waste treatment in oxidation ponds is the results of natural biological processes carried out mainly by bacteria & algae, heterotrophic, autotrophic & zooplankton.

 The microbiological process are carried out by following process:-

▪ Activity in the Photic Zone

▪ Zooplankton activity

▪ Effect of temperature on pond operation.

▪ Heterotrophic activity.

 Aerobic

 Anaerobic

• Activity in different pond zone

• Photic zone:- Chlamydomonas , Euglena, Chlorella, Microactinium, Oscillatoria,

• Zooplankton Zone:- Cladocera , filamentous algae.

• Heterotrophic activity:- Purple –sulfur bacteria

• Aerobic microbial activity results the production of CO2, & anaerobic microbial activity results production of gases such as , H2S, to oxidize organic matter.

4 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

• Effect of temperature on pond :- temperature plays significantly affects in waste degration of pond sediments, below 15 ˚c no methanogenic activity& degradation occurs.

Removal by oxidation of pond

Solid- 1.The effluents need to be treated by filters.

2.Clean sand is deposited afterwards on top of the filter.

Nitrogen- ,denitrification, volatilization as ammonia & algal uptake

Phosphorous-Removal can be increased by treatment with & aluminum salts or with

Bacteria-Long detention time. High pH , ineffectivating of sunlight

Virus-Temperature & solar radiation & high pH

Protozoa-Cyst & oocytes removed by temperature, pH & solar radiation

 Advantages:- . Oxidation of ponds are low initial coast & easy of operation.  Disadvantages:- . Odor problems associated mainly with algal growth. . H2S production & mosquitoes, which are of public health concern.

Trickling filters

 In trickling filters micro-organisms are attached to a solid substratum .  Biofilm comprise trickling filters , rotating biological contactors (RBC) & submerged filters (downflow & upflow filters).  These reactors are used for oxidation of organic matter, nitrification, denitrification or anaerobic digestion of waste water. Biology of trickling filter-

Organisms presents in biofilms :-

 Bacteria:- Pseudomonas, Flavobacterium, Achromobacter, Filamentous Bacteria & Nitrifying bacteria.

 Fungi:- Fusarium , Penicillium, Aspergillus, Mucor & Yeasts.

 Algae:- Ulotrix, Phormidium, Euglena, Chorella.

Protozoa:- Flagellates (Bodo, Monas), Ciliates (Colpidium, Vorticella

5 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

Removal by tricking filters

Bacteria-Removal of by filters , but it is low & erratic.

Viruses-Removed by to the biofilm material

Protozoa-Cysts & oosysts removed by adsorption.

 Advantages:- . Trickling filters are attractive to small communities because of easy operation . Low maintenance cost & relability. . The sludge biofilms can also be easily removed by sedimentation.  Disadvantages:- . High organic loading may to filter clogging as a result of excessive growth of slime bacteria in biofilms. . Excessive biofilm growth can also cause odor problem in trickling filters. . Clogging restricts air circulation .

Activated sludge process

 Activated sludge is a suspended growth process , & adopted world wide as a secondary biological treatment for domestic waste water treatment.  This process consists essentially of an aerobic treatment that oxidizes organic matter to CO2, H2O, NH4 & new cell biomass.  Air is provided by using diffused or mechanical aeration.  Conventional Activated Sludge:-

 Aeration tank:-

 Aerobic oxidation of organic matter is carried out in the tank

 Primary effluent is introduced & mixed with return activated sludge (RAS) to form the mixed liquor.

 Sedimentation tank:-

 This tank is used for the sedimentation of microbial flocks(Sludge).

 A portion of the sludge in the is recycled back to the aeration basin.

6 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

 Features of activated sludge

• Mixed Liquor suspended solids(MLSS) • The total amount of organic & mineral suspended solid including micro organism in the aeration tank in an activated sludge system. • Mixed Liquor Volatile Suspended Solids (MLVSS) • It comprises non microbial organic matter as as dead microorganism & cellular debris. • Food to microorganism ratio(F/M) • It indicates the organic load into the activated sludge system • Hydraulic Retention Time(HRT) • Average time spent by the influent liquid in the aeration tank of the activated sludge. • Sludge Age • Sludge age is the mean resident time of microorganism in the system.

Modification of the conventional activated sludge

• Extended aeration system • The raw material has not treated with primary settling.

7 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

• The system operates at much lower F/M ratio. • Oxidation ditch • It consists of an aeration oval channel with one or more rotating rotors for waste water aeration. • Step aeration • The primary effluent enters the aeration tank through several points & improving its distribution into the tank . • Contact stabilization • Sludge flows to a clarifier & sludge is returned to a stabilization tank. • Completely mixed aeration system • A completely mixed aerated system allows a more uniform aeration of the waste water in the aeration tank. • Pure oxygen aeration • It is based on the principle that the rate of transfer of pure oxygen is higher than that of atmospheric oxygen

• Organism present in activated sludge flocs:-

• Bacteria :- Zooglea, Pseudomonas, Flavobacterium, Corynebacterium, Acinetobactor.

• Fungi:- Penicillium, Cephalosporium, Alternaria

Protozoa:- Aspidisa, Costata.

Removal by activated sludgegen

Nitrogen-Removed by chemical –physical means (breakpoint chlorination or air stripping to remove ammonia) or by biological means (de- nitrification)eria:-

Bacteria-Removed via inactivation , grazing by ciliated protozoa & adsorption to sludge solids or encapsulation within sludge flocks followed by sedimentationruses:-

Viruses-enteric viruses were removed by a conventional activated sludge process

 Advantages:- . Removes organics . Oxidation & nitrification achieved . Biological phosphorous removal . Solids / liquid separation . Stabilization of sludge

8 By Rabiul Alam, Dept. of Microbiology,RGU M.Sc. 2nd semester Generic Elective course (IDC course)-Advanced Microbiology

Disadvantages:- . Does not remove color from industrial waste . Does not removes nutrients . Problem of getting well settled sludge.

For any doubt or clarification, feel free to contact me through

Mail at [email protected]

Phone-8900043436

9 By Rabiul Alam, Dept. of Microbiology,RGU