Question

Describe the role of microbes in sewage treatment plants.

Answer 1

Hint: Sewage treatment is the process by which the contaminants are removed from the municipal wastewater. This uses various physical, chemical and biological methods to remove the contaminants during the process.

Complete answer:

Pollutants are removed from the water using a sewage treatment method. If this is not done, the sewage water containing the organic matter can be released in the water bodies which causes harm to the environment and organisms that live in water. The process of sewage treatment occurs in three stages: primary, secondary and tertiary treatment. 

Primary treatment is associated with the physical separation of sewage into solids and liquid by using a settling basin. This is followed by secondary treatment in which removal of  the dissolved biological compound by the use of microorganisms is carried out from  the liquid sewage. Finally, tertiary treatment is carried out to disinfect the sewage so that it can be released into the environment.

 

When the primary treatment is done, liquid and solid phases get physically separated. After this, the liquid is treated with aeration that leads to decompose organic compounds, and pollutants in the wastewater by aerobic organisms. It involves  nitrification and phosphorous removal. The primary effluent is passed into large aeration tanks where they are continuously mixed and agitated which leads to growth of microbial flocs. 

These  microbes use the organic matter present in wastewater and reduce the BOD  (Biological oxygen demand). BOD is the amount of oxygen that aerobic bacteria utilise to break down biodegradable organic matter into end products such as water and Carbon dioxide. If the BOD is low, the water has low content of organic matter and has low counts of microbial organisms. This effluent is then passed into the settling tank. In the settling tank the bacteria sediments to form activated sludge, a small of which is used as inoculum in aeration tank and rest is digested by anaerobic bacteria. These anaerobic bacteria produce methane, hydrogen sulphide and carbon dioxide during the digestion process.

Note: In nitrification during sewage treatment, ammonium is oxidized to nitrite by Nitrosomonas.spp, and nitrite is further oxidized to nitrate by Nitrobacter.spp. Micro-organisms usually use aerobic metabolism to degrade the biological matter in the liquid sludge.