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Certain systems add an oxygen-deprivation step (more tanks) for further separation and treatment, as some microorganisms work best without oxygen. More settling tanks are then used before chlorine is added to the flow.
The chlorine kills off most remaining pollutants, but it must be nullified by chemicals before the flow, now treated effluent, is discharged into a stream or reused on, say, a golf course.
Many plants make use of a “tertiary phase.” This is also called “advanced treatment.” It involves the nutrient removal of nitrogen, phosphorus, plus the removal of any toxic metals or chemicals
See CLEVENGER’S, Page A8
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