1 minute

5 minutes

2-4 hours

12 hours

sludge digestion tank

sedimentation tank

activated sludge treatment

trickling filters

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