only (i)

(i) and (ii)

(i) and (iii)

only (iii)

oxidation pond

oxidation ditch

aerated lagoons

trickling filters

aerobic only

anaerobic only

aerobic in lower compartment and anaerobic in upper compartment

anaerobic in lower compartment and aerobic in upper compartment

aerobic bacteria only

algae only

dual action of aerobic bacteria and anaerobic bacteria

sedimentation

4-8 hours

24 hours

10 to 15 days

3 months