Table 8.4 Central and cluster treatment options

Wastewater conditioning	Primary treatment	Secondary treatment	Tertiary treatment	Advanced treatment	Sludge treatment
Screening and grit removal	Imhoff tank Clarigester	Activated sludge: standard aeration extended aeration oxidation ditches sequencing batch reactors	Sand filters (following activated sludge, biofilter or pond systems)	Nitrogen removal: denitrifying sequencing batch reactors denitrifying sand filters zeolite filters	Septage: burial chemical treatment and landfilling
	Sedimentation (large capacity septic tank) Sedimentation with chemical addition	Biofilters: trickling filter (biological filter) rotating biological contactor	Disinfection (pathogen removal): chlorination UV ozone	Phosphate removal: chemical stripping biological stripping amended soil absorption	Raw sludges: anaerobic digestion digestion and compost treatment other treatment technologies
	Oxidation ponds (primary treatment)	Sand filters: intermittent sand filter recirculating sand filter	Oxidation ponds (maturation treatment)	Membrane filtration	Biosolids: aerobic digestion digestion and compost treatment
		Oxidation ponds (secondary treatment)	Overland flow