requirements. NPDES permits require discharging facilities to limit or treat effluent to the levels that result from using the most effective treatment technologies possible at a practical cost to mitigate the effects of discharges on the receiving waters. EPA has published technology-based regulations, called "effluent guidelines", for 59 industrial categories. The agency reviews the standards annually, conducts research on various categories, and makes revisions as appropriate. Noncompliance with these standards and all other conditions in the permits is punishable by law. Each year, effluent guidelines regulations prevent billions of pounds of contaminants from being released into bodies of water. EPA regulations require effluent limitations to be expressed as mass-based limits (rather than concentration-based limits) in the permits, so that discharging facilities will not use dilution as a substitute for treatment. In cases where setting mass-based limits are infeasible, the permit authority must set conditions in the permit that prohibit dilution. Pretreatment When pretreating effluent, it is difficult to reduce expenses, increase productivity, adhere to stringent standards, and prevent discharge of byproducts. Furthermore, depletion of clean, fresh, accessible water is a global issue, but evolving technology can help prevent this because improving treatment methods allows for re-use of water. Additionally, waste-to-energy technology transforms organic matter into usable electricity, heat, or fuel. Treatments also exist to remove certain elements, compounds, salts, and minerals from effluent. See also Effluent guidelines (U.S. wastewater regulations) Effluent limitation Wastewater References Environmental science Environmental engineering Water pollution