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basics of microbiology

1. Sewage Microbiology and Treatment Sewage: Types and Characteristics Sewage is a mixture of domestic and industrial wastes plus drainage water from rainfall. It contains human and animal excreta, household washing waters, hospital and scienti fi c research laboratory wastes, petroleum wastes, industrial wastes agri -cultural wastes, and microorganisms. Chemically, sewage contains organic contents including carbohydrates, fats and proteins, inorganic compounds, heavy metal residues etc. The modern technology and lifestyle have changed the sewage characteristics of wastewater. For example, the use of synthetic detergents in place of soap can adversely affect the indigenous microbial population required for effective sewage treatment. Therefore, the exact types and characterization of sewage is an important aspect to evaluate its pollution potential, designing an appropriate sewage processing plant, monitoring the effectiveness of the treatment plant and stopping the pollution of the receiving water body. It also helps to establish a cost-effective waste management system.

2. Classi fi cation of sewage Sewage can be categorized into four groups based on origin, harmfulness, contamination stability, and human activity. Sewage can be grouped into the following types based on their sources of origin : Domestic : sewage originates from public toilets, households, plants, and animal wastes. Industrial : wastewater generates during all types of industrial processes. Precipitation: It is rain and melt water that contains several atmospheric contaminations (i.e. dust, gaseous substances, microbiological (i.e. bacteria, viruses, fungal and protozoa), surface and street run-offs. Sewage may be classi fi ed into the following groups based on adverse health effects : Directly harmful : substances responsible for direct impact on health. Indirectly harmful : leads to a reduction of oxygen in the water below the critical organism’s requirement.

3. Sewage can be grouped into the following groups based on the stability of contaminates present in wastewater : Degradable : organic substances that undergo chemical transformation to form simple substances. Non-degradable : substances that are not decomposed by microorganisms and do not yield to any chemical transformation. Sewage can be grouped into the following categories based on human activities : Urban and domestic- sources: Houses, food serving facilities, and hospitals. Rural - source: excess chemical fertilizers from fields, and animal farms. Industrial - source: various kinds of manufacturing and processing industries are the main source of Several toxic compounds released in wastewater. Radioactive - source: radioactive compounds may be contributed in the sewage by health diagnostic facilities, scientific experiments, or research and nuclear reactors. Radioactive substances are hazardous and require special kinds of storage methods and disposal protocols.

4. Microbiology of Sewage Bacteria Sewage treatment vats contain both bene fi cial and harmful bacteria due to their arrival with sewage water. Bene fi cial bacteria: Certain biofilm-forming bacteria including Pseudomonas, Chromobacter , Flavobacterium, and Zooglea are present in the secondary treatment process (trickling fi lter phase), and considered to be bene fi cial in the removal of organic content from sewage. In addition, nitrogen-removing bacteria like Nitrosomonas and Nitrobacter (nitri fi ers), Thiobacillus ( denitri fi er ), Desulfotomaculum , and Desulfovibrio ( sulfate reducer) are also found in sewage. Harmful bacteria : Bacteria are responsible for numerous human animal and plant diseases by infecting their host via ingestion of contaminated water or food, fecal -oral route, etc. Human pathogens cause waterborne infections. For example, some pathogenic bacteria like Escherichia coli serotype O157 : H7(causes food poisoning and diarrhea ), Salmonella typhi (typhoid), and Vibrio cholera (cholera) can be found in sewage due to fecal contamination. E.coli is used as a fecal indicator. During disinfection, most of these microorganisms are destroyed and removed from sewage.

5. Fungi Fungi are single or multi-cellular eukaryotic organisms found in fi xed fi lm processes (i.e. Fusarium aquarductuum , Trichosporon cutaneum , Geotrichium candidumm , Ascoidea rubescenes and Subarromyces splendens ) and take part in the removal of carbonaceous materials from sewage. Protozoa Protozoa such as amoebae, flagellates, and ciliates unicellular eukaryotic organisms are found present throughout the complete sewage treatment process. They mainly feed on organic particulate matter. The most commonly ciliated protozoa such as Vorticella, Carchesium and Opercularia play a very important role in maintaining the slime layer in trickling filter systems. In addition, protozoa play a predatory role in controlling bacterial population density. In general, protozoa are useful in sewage treatment but can be harmful to human beings if ingested. For example, protozoan parasites including Giardia lamblia is a waterborne pathogens found in sewage and its cysts enter the water supply through fecal contamination and cause giardiasis.

6. Viruses Sewage may become contaminated by more than 140 types of enteric viruses. The viral pathogen enters into the human body through the fecal-oral route, multiplies in the gastrointestinal tract, and is excreted in large numbers in the fecal matter of the infected host.

7. Municipal Wastewater Treatment Wastewater Treatment Process Step by Step Step One: a. Wastewater collection Wastewater collection is the first step in the process. The collection system is normally put in place by homeowners, municipal administration as well as business owners. They ensure that wastewater is collected together and then directed to the central point. This process is normally done in a structured way. The wastewater is directed using the underground drainage systems into the treatment plant. The process of transporting this wastewater into the treatment plant should be done in hygienic conditions. It is important to ensure that the pipes or tracks do not leak and individuals offering these services should put on protective clothing.

8. b. Pre-Treatment This is the very second step in raw sewage treatment. It is meant to remove items such as broken bottles, wipes, sanitary items, and diapers among others which may destroy the equipment during the process. At this stage, grit and sand are removed too. It is a very basic process in Wastewater Treatment Plants (WWTP). After it is removed, it is then rinsed in the sewer. Pre-treatment entails the screening and then removal of large particles or debris from raw sewage. This is because all these debris is not readily biodegradable through the bacteria process. The debris is then dried up and then incinerated. Sand and grit are then settled out in the tanks as indicated above.

9. Wastewater contains many dirty substances that may cause foul smell after some time. This smell is not pleasing to the environment and this is why odor control is very important. To have a surrounding environment that is free of the odor smell, the odor treatment process shall be initiated. The process is mainly initiated at the treatment plant. This is done by containing the wastewater and treating it with chemicals. This chemical will automatically neutralize the smell-producing elements. The most common chemicals used for this purpose are hydrogen peroxide, ozone, and chlorine dioxide. c. Odor Control

10. d. Screening Screening is the next step in the wastewater treatment process. It involves removing all the large objects that may have remained after doing pre-treatment. In this process, everything is almost the same as in the treatment process. The difference is that screening is more advanced. It involves the removal of all solid products. There are designed equipments which are specially designed to perform all these functions of getting rid of unwanted products in the wastewater. These solid wastes are then transported and disposed away after being removed from the wastewater. They are normally disposed of in landfills.

11. Step Two: Primary Sewage Treatment This is a settlement stage that involves the separation of solid macrobiotic matter from wastewater. The process is simply done by pouring wastewater into the big tanks so that the solid matter can settle on the surface of the tank. At this stage, the water is classified into two. One is the organic matter, which is in solid form and the wastewater (now without solids). T his is done by putting it in a large tank that is called a settlement tank. Since the wastes are denser, they sink at the bottom of the tank. The wastes that sink at the bottom of this tank are known as sludge. The wastes are then pushed to the center by large scrappers which continuously remove them from the bottom. At the top, there is another layer of fats which floats since it is less dense than water. This layer of fats forms a crust. The water between the crust and the sludge, which is now homogenous, is taken to for secondary treatment. This makes the treatment more proficient.

12. Step Three: Secondary Sewage Treatment In this stage, Oxygen (O 2 ) is introduced into the water. In simple terms organic compounds are broken down into a form that is easier to remove from the water. This helps break down the sludge that may have escaped in stage 2. Secondary treatment is also known as activated sludge process . At this point, seed sludge is added into the wastewater to break it down further. First, pumping air into the huge  aeration tanks  that has a mix of wastewater with seed sludge. A small amount is pumped in to fuel the growth of bacteria which use oxygen. It also fuels the growth of microorganisms which consume all the remaining organic matter. After a short while, the production of debris which will normally settle down at the bottom of the large tank. Water can pass through the huge tank in three to six hours Humus and the dead bacteria settle out in another chamber for extra treatment.

13. Bio-solids handling The final solid matter that settles down after the primary and secondary treatment process, is then directed into the digesters. Digesters are then heated strongly at room temperature. These solid wastes are heated. They then undergo the process of anaerobic digestion. At this stage, methane gas is produced and the formation of nutrient-rich bio-solids is also experienced. They are then recycled and then dewatered to the local firms. This methane gas that is formed is mostly used as a source of energy. It is used in the treatment plant and can also produce some electricity in driving plant equipment. In the boilers, the gas is also necessary since it helps generate some heat for digesters

14. Step Four: Tertiary Treatment  Tertiary treatment is very important especially where the discharge points are very sensitive. These sensitive points include streams or dams where the water will be used directly by plants animals and people.This vital stage involves treatments such as a. Chlorination b. Ozone treatment c. Use of Ultra Violet light to disinfect d. Reducing the level of Nitrogen At the tertiary treatment stage all impurities are removed from the wastewater. This stage is almost similar to that used in the drinking water treatment plant. It ensures that 99 percent of impurities are removed. At this stage wastewater is treated to the extent that it produces effluent water which has almost same quality as that of drinking water. The process is a bit more expensive because it requires special equipment, highly skilled and well trained equipment operators and strong chemicals together with a steady supply of energy.

15. Disinfection After going through all the processes, you can still find some disease-causing organisms. To completely eliminate and remove all these organisms, wastewater is then disinfected for about 20-25 minutes inside tanks with a mixture of sodium hypochlorite and chlorine. The process of disinfecting is an integral part of the wastewater treatment process. This is because it protects the health of local people and animals who may use this water for other purposes.

16. Step Five: Sludge Treatment The produced and collected sludge at the primary and secondary levels requires a high concentration and thickening process. This is achieved by putting them into the thickening tanks letting them settle down and then separating them later from the water. The process of sludge treatment may take up to 24 hours. After treating the sludge, the remaining water will then be collected and reversed back to the large aeration tank to enable further treatment. After treatment of sludge, it is then sent back to the environment for agricultural use. From this point, the water is safe for use and is therefore released into the river.