Ecotoxicological assessment of UV-C/Oxidant processes for advanced treatment of aquaculture effluents

• UV-C/oxidant AOPs were evaluated for advanced aquaculture effluent treatment. • Sulfate-radical and PAA-based AOPs ensured high Daphnia magna biocompatibility. • Growth inhibition in P. subcapitata was transient and reversible upon dilution. • Residual oxidants and DBPs were the primary drivers of acute effluent toxicity. • RAS recirculation provides a natural safety margin for AOP process integration. The growth of the aquaculture sector poses challenges in maintaining product quality, particularly regarding contamination, which risks aquatic organisms and human health. Advanced oxidation processes using UV-C radiation can remove persistent compounds and pathogens from aqueous matrices through the generation of reactive species. However, their chemical non-selectivity may produce toxic disinfection by-products (DBPs), which require cautious ecotoxicological assessment. This study aimed to evaluate the ecotoxicological effects of UV-C/oxidant processes on aquaculture effluents by employing survival assays with Daphnia magna (D. magna) and growth inhibition assays with Pseudokirchneriella subcapitata (P. subcapitata) . UV-C treatment of synthetic and real aquaculture effluents was intensified by hydrogen peroxide (H 2 O 2 ), peracetic acid (PAA), sodium hypochlorite (NaClO), potassium peroxymonosulfate (PMS), and sodium persulfate (PS). UV-C treatment combined with PAA, PMS, or PS showed promising reductions in toxicity and high D. magna survival rates, whereas treatments with H 2 O 2 and NaClO resulted in significant adverse effects on its survival. This is likely due to residual oxidants and disinfection by-products, as dark controls showed lower toxicity, and UV-C alone had a negligible effect. For P. subcapitata bioassays, UV-C/PMS and UV-C/PS were identified as the most suitable treatments. Our findings support the use of UV-C-based AOPs for aquaculture effluent treatment, with prudent selection and addition levels, while highlighting dilution via recirculation in recirculating aquaculture systems (RAS) as an intrinsic advantage for mitigating relevant ecotoxicological risks.