In what stage of wastewater treatment is 90 percent of the oxygen-demanding substances removed from the waste by microbes? primary treatment. secondary treatment. tertiary treatment. septic tank treatment.
I think the correct answer would be secondary treatment. Oftentimes at this stage, microbes are being used to treat the wastewater. It is the heart of the process since a big part of the harmful substances are lowered at this stage. Hope this helps.
