Secondary sewage treatment is mainly a :
- Mechanical process
- Chemical process
- Biological process
- Physical process
Answer
(3) Biological process
Solution
Primary treatment ⇒ physical removal of particles by filtration and sedimentation.
Secondary treatment ⇒ aerobic microbes grow as flocs and consume the organic matter, reducing the BOD; the sludge is then digested by anaerobic bacteria.
∴ As per NCERT, secondary treatment is a biological treatment.
Answer: (3)