What biological process do microorganisms primarily use to treat wastewater?

Microorganisms primarily use aerobic respiration as the biological process to treat wastewater due to the presence of oxygen in aeration tanks within wastewater treatment facilities. During aerobic respiration, microorganisms such as bacteria consume organic matter, breaking it down while utilizing oxygen. This process results in the conversion of organic pollutants into carbon dioxide, water, and biomass, which helps to reduce the levels of harmful contaminants in wastewater.

Aerobic respiration is highly effective because it allows microorganisms to efficiently generate energy from organic materials, leading to a significant reduction in biochemical oxygen demand (BOD). A lower BOD indicates improved water quality and a lesser impact on receiving water bodies after discharge.

Other processes mentioned, like alkaline hydrolysis and fermentation, play specific roles in wastewater treatment but are not the primary biological method utilized for treating most wastewater. Alkaline hydrolysis is more associated with sludge treatment, while fermentation occurs in anaerobic conditions and typically generates energy without the use of oxygen, which is not the mechanism favored in conventional wastewater treatment operations. Evaporation is a physical process, not a biological one, and does not involve microorganisms, making it irrelevant in this context.