The “double-edged sword” effect of waste biomass: An ecological trap of photodriven persistent free radical generation from chlorophenols

While the role of waste biomass in promoting the photodegradation of organic pollutants is recognized, its potential to simultaneously generate hazardous byproducts, particularly environmentally persistent free radicals (EPFRs), remains an underappreciated ecological risk. In this study, we uncover the "dual-edged sword" effect of waste biomass in environmental remediation: while facilitating photochemical degradation of chlorophenols (CPs), it inadvertently generates ecotoxic risks via EPFRs. Non-soluble organic matter (NOM) and dissolved organic matter (DOM) derived from biomass (rice straw, corn straw) enhance CPs degradation under visible light via distinct pathways. NOM components (e.g., flavonoids, oxygenated groups) promote reactive oxygen species (ROS) generation, driving CPs dechlorination and hydroxylation, whereas DOM-derived humic-like substances mediate degradation through triplet-state reactions. Critically, this process simultaneously produces stable semi-quinone-type EPFRs (g ≈ 2.0065), with biomass composition dictating their persistence. Intermediate tetrachlorohydroquinone (TCHQ) is identified as a key EPFRs precursor under •O₂^- dominated conditions, exhibiting high aquatic toxicity of TCHQ (LC50/EC50 < 10 mg/L) per ECOSAR simulations. Despite achieving > 40 % CPs photodegradation, the co-occurrence of EPFRs and toxic intermediates underscores the need to balance remediation efficiency against ecological hazards. These findings provide essential insights for optimizing biomass-based pollutant control strategies by addressing both beneficial and adverse effects.