Effluent

Effluent is wastewater discharged from a point source, including sewage works, industrial plants, and ships, into a receiving water. Its pollutant load is characterized by biochemical and chemical oxygen demand, suspended solids, nutrients, faecal indicator bacteria, and specific toxicants. In the United States, effluent discharge to surface waters requires an NPDES permit under Clean Water Act section 402, carrying technology-based and water-quality-based effluent limits. Where the receiving water is impaired, wasteload allocations from a total maximum daily load tighten those limits. At sea, ship sewage effluent is governed by MARPOL Annex IV, which limits discharge by distance from land and treatment-plant performance.