Question

Large quantities of sewage are generated every day in cities as well as in towns and are treated in Sewage Treatment Plants (STPs) to make them less polluting. Given below is the flow diagram of stages of STP.

Study the flow diagram and answer the questions that follow:

1.   
   1. Why is primary effluent passed into large aeration tanks?   [1]
   2. What is the 'sediment' formed, referred to as? Mention its significance.   [1]
   3. Explain the final step in the settling tank before the treated effluent is released into water bodies.   [1]
2. Name any two organisms commonly used as biofertilisers, belonging to different kingdoms. Write how each one acts as a biofertiliser.   [2]
3. Many patterns of inheritance deviate considerably from the pattern of inheritance as explained by Mendel. List any four such inheritance patterns and explain any three with the help of an example each.

Answer 1

1.    
   1. The main effluent is sent into a sizable aeration tank where floes of bacteria and fungi in mesh-like structures aerobically digest the effluent to reduce its BOD by breaking down the organic materials.
   2. The sediment produced is termed activated sludge. A portion of this is recirculated into the aeration tank to function as the inoculum.
   3. The final step in the settling tank includes anaerobic digestion carried out by fungi and bacteria in anaerobic sludge digesters. Then, the treated effluent may be released into natural water bodies.
2. Rhizobium creates a symbiotic relationship with legumes to fix atmospheric nitrogen into organic forms that plants can use.
   While freely existing in the soil and increasing its nitrogen content, Azospirillum fixes nitrogen from the atmosphere.