AOPs are essential for bridging the gap between biological limitations and strict environmental standards, ensuring complete treatment of persistent pollutants. When AOP is Needed When wastewater contains non-biodegradable or slowly biodegradable organics. When effluents must meet very stringent discharge or reuse regulations. For industrial sectors with high-strength effluents: textile, pharma, petrochemicals, pulp & paper, landfill leachate. As a pretreatment before biological processes, or as a final polishing step after them.