NEET BIOLOGY

Detailed explanation-1: -(iii)The sediment is called primary sludge and supernatant is effluent.

Detailed explanation-2: -So, the correct answer is ‘Primary sludge’.

Detailed explanation-3: -Primary sludge is generated by the separation of settleable solids from the raw wastewater during the primary sedimentation treatment process. The total solids concentration in raw primary sludge ranges between 5% and 9%, and is typically 6%.

Detailed explanation-4: -Primary sludge is generated from chemical precipitation, sedimentation, and other primary processes, whereas secondary sludge is the activated waste biomass resulting from biological treatments. Some sewage plants also receive septage or septic tank solids from household on-site wastewater treatment systems.

Detailed explanation-5: -Primary sewage water treatment entails filtration and sedimentation of solid waste inside the water. Secondary sewage water treatment includes biofiltration, oxidation, and aeration. Tertiary sewage water treatment involves the removal of inorganic chemicals such as nitrogen and phosphorus.