Why do anaerobic ponds need long detention times?

Anaerobic ponds require long detention times primarily because the bacteria responsible for the breakdown of biochemical oxygen demand (BOD₅) grow very slowly. In an anaerobic environment, these bacteria operate without oxygen, leading to a slower metabolic rate compared to aerobic processes where oxygen is present. This slower growth rate means that for effective treatment of wastewater — particularly in reducing organic matter and stabilizing sludge — the retention time in the pond must be extended.

Long detention times allow for sufficient contact between the wastewater and the anaerobic microorganisms, facilitating the breakdown of organic matter over time. This is crucial to achieve effective treatment before the effluent is discharged or further treated. Shorter detention times would not provide enough opportunity for these slow-growing bacteria to perform their essential functions adequately, leading to insufficient treatment outcomes.