UV254 triggers chloroacetic acids degradation to generate degrading products for Chlorella sorokiniana growth: mechanism and performance evaluation

This study investigated the UV 254 irradiation degradation of chloroacetic acids (CAAs), specifically monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA), and evaluated the ecological impact of their degradation products on Chlorella sorokiniana (CS). The degradation followed first-order kinetics, with dechlorination efficiencies of 91.2% for MCAA, 92.9% for DCAA, and 92.4% for TCAA. TCAA was degraded fastest due to its higher chlorine content. Initial pH (3–10) had minimal influence, whereas lower concentrations (0.25   mM) led to slower degradation. Hydroxyl radicals (•OH) were identified as the dominant reactive species via electron paramagnetic resonance analysis. Dechlorination generated Cl⁻ and HCl, resulting in acidification and increased toxicity. Total organic carbon (TOC) analysis indicated nearly complete mineralization. Untreated CAAs significantly inhibited microalgal growth and photosynthesis, while post-degradation pH adjustment (to pH > 4) mitigated toxicity and enabled microalgal assimilation, with CS culture pH further increasing to 9–10, thereby facilitating self-buffered bioremediation. These findings confirm the effectiveness of UV 254 degradation on CAAs and provide valuable guidance for ecological safety in aquatic ecosystem management.