Question

Secondary sewage treatment is mainly

• A. Chemical process
• B. Mechanical process
• C. Biological process
• D. Physical process

Answer 1

Answer: (C)

Biological process

• Sewage treatment is a process in which sewage is treated in order to remove its harmful constituents and making it environmentally safe.
  
• The secondary treatment is carried by certain microorganisms which remove all the suspended and dissolved biological matter. Chlorination is done to remove microorganisms from the effluent prior to its discharge for the tertiary treatment.
  

So, the correct option is 'Biological process'.