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In this study, the photogeneration of OH and 1O 2 and the degradation mechanism of organic pollutants in biochar suspension under the simulated solar light irradiations were investigated. Biochar derived from rice husk with 550 °C of charring temperature (R550) was selected to degrade benzoic acid. It was found that 10 g/L of R550 could degrade 78.7% of benzoic acid within 360 min at pH 3, and the degradation efficiency was promoted to 95.2% as ultraviolet (UV) presented. By checking the production of p-hydroxybenzoic acid, UV accelerated the production of OH, which was confirmed by the enhanced degradation efficiency of 59.2% caused by the evaluated OH as UV appeared. The furfuryl alcohol loss in the R550 suspension under light irradiations testified to the production of 1O 2 , which contributed to 9.3% of benzoic acid degradation. Oxidization treatment using gradient concentrations of H 2 O 2 was employed to enhance the ageing process of biochar. As the ageing processed, the biochar possessed a declined performance towards OH production from O 2 activation and the radical degradation of organic pollutants. As a contrast, the evaluated content of 1O 2 and enhanced non-radical degradation of organic pollutants was reached as UV presented. The further study indicated that phenolic hydroxyl groups on biochar facilitated the production of OH via the electron transfer, and quinone like structures (C=O) on biochar boosted the generation of 1O 2 via the energy transfer. Moreover, upon eliminating the BA degradation, persistent free radicals were formed on biochar, which was enhanced owing to the presence of UV. Unlabelled Image • Degradation of organic contaminants by biochar was enhanced by UV. • UV triggered the production of OH and 1O 2 from biochar suspension. • Quinone-type structures on biochar induced the production of 1O 2. • The ageing favored the production of 1O 2 under light irradiations. • The ageing retarded OH formation and radical degradation of organic contaminants. [ABSTRACT FROM AUTHOR]