Reduction of Biochemical Oxygen Demand in Wastewater Effluents Using UV LED Photolysis and Advanced Oxidation Processes

Removal of organic loading in wastewater effluent is a critical objective for treatment facilities to ensure compliance with local regulations and environmental safety. This study investigated the efficacy of 275-280 nm UV LED irradiation for reducing bulk organic matter, quantified as biochemical oxygen demand (BOD5) and carbonaceous biochemical oxygen demand (cBOD5), in municipal wastewater effluent. The research encompassed both bench-scale and full-scale experimental conditions. Bench-scale evaluations utilized collimated beam and flow-through UV LED reactors operating at 275 nm, with fluences ranging from 250 to 5000 mJ cm-2. These experiments were conducted on primary and secondary effluent matrices, both with and without the addition of chemical oxidants such as chlorine. Furthermore,

the treatment performance for secondary effluent was assessed using a full-scale flow-through 280 nm UV LED reactor, operating at an approximate fluence of 148 mJ cm-2 and a flow rate of 545 m3 day-1. The findings demonstrated that UV-C LED irradiation effectively reduces effluent BOD in municipal wastewater matrices, achieving reductions of up to 52% at both bench and full scales. Mechanistic insights revealed a shift in the humic index within the fluorescence profile of UV-exposed samples, suggesting the degradation of higher molecular weight organic compounds into lower molecular weight, protein-like substances. This research provides valuable guidance on the application of UV LED technology for advanced wastewater treatment.

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