Table II.

Efficiencies of treatment processes for domestic sewage

Treatment	BOD (%)	Suspended solids (%)	Escherichia coli (%)
Plain sedimentation	25–40	40–70	25–75
Chemical precipitation	50–85	70–90	40–80
High-rate trickling filtration preceded and followed by plain sedimentation	65–95	65–92	80–95
Low-rate trickling filtration preceded and followed by plain sedimentation	80–95	70–92	90–95
High-rate activated sludge preceded and followed by plain sedimentation	65–95	65–95	80–95
Conventional activated sludge preceded and followed by plain sedimentation	75–95	85–95	90–98
Chlorination of biologically treated sewage	–	–	98–99