Photoelectrocatalytic coupled chlorine degradation of tetracycline hydrochloride in recirculating aquaculture system (RAS)

With the rapid development of intensive aquaculture systems, the widespread misuse of antibiotics has raised significant ecological and human health concerns. However, effective methods for antibiotic removal in recirculating aquaculture systems (RAS) remain scarcely reported. This study systematically constructed three distinct degradation systems - photocatalytic (P), photoelectrocatalytic (PE), and photoelectrocatalytic coupled with chlorine (PE-Cl − ) - based on TiO 2 nanotube arrays for efficient tetracycline hydrochloride (TCH) degradation in RAS. Results demonstrated that the PE-Cl − system exhibited superior TCH degradation efficiency, following first-order reaction kinetics. Key operational parameters were optimized, revealing that NaCl concentration (optimal at 30 mM) and acidic conditions (pH = 3, achieving 97.5 % degradation) significantly enhanced system performance, while humic acid (HA), sodium acetate (SA), and actual aquaculture water showed minimal interference. Radical quenching experiments identified hydroxyl radicals (•OH) as the predominant reactive species contributing to TCH degradation. The degradation pathways primarily involved demethylation, hydroxylation, and deamination reactions. Importantly, toxicity assessment using Chlorella vulgaris indicated significantly reduced ecotoxicity of the degradation byproducts ( p < 0.001). This study provides both theoretical foundations and practical solutions for addressing persistent organic pollutants in RAS, offering valuable insights for sustainable aquaculture water treatment. • Photoelectrocatalytic coupled chlorine system effectively degraded tetra cycline hydrochloride in RAS. • Hydroxyl radicals (-OH) in photoelectrocatalytically coupled chlorine systems contribute to TCH degradation. • Chlorella toxicity test evaluated the reduction of toxicity after TCH degradation. • Three possible degradation pathways for tetracycline hydrochloride are proposed.