Difference between primary and secondary sludge

primary sludge
1. it is sludge formed during primary sewage treatment.
2. it does not possess flocs of decomposer microbes.
3. it does not require aeration.
4. little decomposition has occurred during formation of primary sludge.
activated sludge
1. it is sludge formed during secondary sewage treatment.
2. it possess flocs of decomposer microbes.
3. formation of activated sludge requires aeration.
4. a lot of decomposition has occurred during formation of activated sludge.