According to the Clean Water Act (CWA), what is the maximum allowed BOD for secondary treatment effluent?

The maximum allowed Biochemical Oxygen Demand (BOD) for secondary treatment effluent according to the Clean Water Act is set at 30 mg/L. This standard is significant as it establishes a benchmark for the quality of treated wastewater that can be discharged into the environment. Secondary treatment processes are primarily biological systems designed to remove organic matter and pathogens from wastewater, and the 30 mg/L limit reflects the acceptable level of organic pollutants that should remain after these processes.

Maintaining BOD levels at or below this threshold is crucial because high levels of BOD in effluents can lead to oxygen depletion in receiving waters, adversely affecting aquatic life. The regulation is part of a broader goal under the CWA to protect water quality and ensure that discharges do not harm the environment or public health.

Other potential limits such as 10 mg/L, 20 mg/L, or 50 mg/L do not align with the CWA standards for secondary treatment effluent and may represent different treatment levels or regulatory frameworks. The 30 mg/L limit effectively balances environmental protection with the practicality of treatment processes used in standard wastewater treatment facilities.