Application of an AOP process solar UV/NaOCl as tertiary phase to biologically treated wastewater

Abstract

This study focuses on optimizing a solar-driven Advanced Oxidation Process (AOP) using sodium hypochlorite (NaOCl) for the tertiary treatment of biologically treated wastewater. The aim was to assess how key parameters sunlight exposure, pH level, NaOCl concentration, and the initial Total Organic Carbon (TOC) load influence the process efficiency. The results clearly demonstrate a synergistic effect when sunlight and NaOCl are combined, achieving around 40% TOC removal in just 30 minutes, compared to minimal degradation when either component was used alone. Among the tested pH values, acidic conditions (pH 3) produced the highest removal efficiency around 65.6%, confirming that the photolysis of NaOCl species under low pH significantly enhances radical formation. The study also shows that increasing the oxidant concentration improves TOC removal, with optimal performance observed at 1000 μM NaOCl (removal around 72.22%). Under optimized conditions acidic pH, 1000 μM NaOCl, and solar irradiation the system achieved impressive TOC reductions even at high initial concentrations. At 98 ppm, up to 82.96% of TOC was eliminated, highlighting the process’s effecacy across a range of pollutant loads. Additional improvements were observed in other water quality parameters, including COD, BOD₅, turbidity, and conductivity, suggesting the treated water meets quality standards for restricted reuse. Overall, the solar UV/Chlorine AOP proves to be a highly effective, low-cost, economic, and sustainable treatment solution, especially suitable for sun-rich regions seeking to enhance wastewater reuse and environmental protection.