What is the maximum suspended solids concentration allowed for secondary treatment under the CWA?

The correct answer is based on regulatory standards established under the Clean Water Act (CWA), which mandates specific effluent limitations for sewage treatment plants. For secondary treatment, the maximum allowable concentration of suspended solids is set at 30 mg/L. This standard is part of the criteria to ensure that wastewater treatment facilities effectively reduce pollutants before discharge, contributing to water quality standards for receiving waters.

Secondary treatment focuses on removing dissolved and suspended organic matter, and achieving this limit is crucial for minimizing environmental impact. The 30 mg/L threshold balances treatment effectiveness with practical feasibility for wastewater treatment plants. This limit helps safeguard water bodies from the detrimental effects of excess solid waste, which can lead to problems like oxygen depletion and harm to aquatic life.

The other options indicate different levels of suspended solids that are either more stringent than necessary or are not applicable under CWA secondary treatment regulations, ensuring that testing and compliance focus on established standards. By adhering to the 30 mg/L maximum, facilities aim to meet environmental protection goals while maintaining operational viability.