Explain why some times foaming is seen in river water near the place the place where sewage water is poured after tratement ?

Explanation

Detergents have long hydrocarbon chains. If their hydrocarbon chain is highly branched. Then bacteria cannot degrade this easily. Such detergents are non-biodegradable. Slow degradation of detergents leads to their accournlation.
These non-biodegradable detergents persist in water even after treatement and cause foarming in rivers, ponds and their wate get polluted. In order to overcome this issue branching of the hydrocarbon chain is k controlled and kept to minimum.