The domestic sewage in large cities  
1. When treated in STPs does not really require the aeration step as the sewage contains adequate oxygen.
2. Has very high amounts of suspended solids and dissolved salts.
3. Has a high BOD as it contains both aerobic and anaerobic bacteria.
4. Is processed by aerobic and then anaerobic bacteria in the secondary treatment in sewage treatment plants (STPs). 

Besides paddy fields, cyanobacteria are also found inside vegetative part of
1. Pinus
2. Cycas
3. Equisetum
4. Psilotum

A good producer of citric acid is 
1. Aspergillus
2. Pseudomonas
3. Clostridium
4. Saccharomyces 

During sewage treatment, biogases are produced which include :
1. Methane, hydrogen sulphide, carbon dioxide
2. Methane, oxygen, hydrogen sulphide
3. Hydrogen sulphide, methane, sulphur dioxide
4. Hydrogen sulphide, nitrogen, methane 

What gases are produced in anaerobic sludge digesters?  

1. Methane and CO₂.
2. Methane, Hydrogen sulphide and CO₂.
3. Methane, Hydrogen sulphide and CO.
4. Hydrogen sulphide and CO₂. 

Match the following list of microbes and their importance.

    (a) (b) (c) (d)
1. (iii) (i) (iv) (ii)
2. (iii) (iv) (i) (ii)
3. (iv) (iii) (ii) (i)
4. (iv) (ii) (i) (iii)

The primitive prokaryotes responsible for the production of biogas from the dung of ruminant animals include the:

Which of the following is wrongly matched in the given table?

Match Column I with Column II and select the correct option using the codes given below:

Codes:

Which of the following, in sewage treatment, removes suspended solids?
1. Secondary treatment
2. Primary treatment
3. Sludge treatment
4. Tertiary treatment