Trickling Filter Cylindrical vat filled with rocks, coarse gravel, on top, and finer particles towards the bottom. Revolving arms of pipes spray water from settling lagoon. Activated Sludge Reactor Suspended aerated microbial culture treats incoming waste water.
Some culture is recycled into effluent stream.
Sludge Product of settling of solids from both primary and secondary treatment processes. Detergents are more soluble in water and do not form insoluble precipitates with Ca and Mg.