Question

Differentiate between the following:

Primary and Secondary treatment of sewage in 'wastewater plants'

Answer 1

Basis of Difference	Primary Treatment	Secondary Treatment
Nature	Physical process.	Biological process.
Main method	Filtration and sedimentation remove suspended solids.	Microbes decompose organic matter in the effluent.
Microbial activity	Microbes are not deliberately used to digest the sewage at this stage.	Aerobic microbes grow in aeration tanks and form flocs.
Main products	Primary sludge and liquid effluent.	Activated sludge and treated effluent with reduced BOD.
Next step	The effluent proceeds to secondary treatment.	Settled sludge is partly recycled as inoculum; the effluent may proceed to tertiary treatment.