Conversion and impact of dissolved organic matters in a heterogeneous catalytic peroxymonosulfate system for pollutant degradation

•The effect of dissolved organic matters (DOM) on organic degradation was explored.•Oxidation pathway of different DOM compounds was elucidated.•Evolution of DOM and inhibition mechanisms to pollutant degradation were revealed.•CHO-, CHON-, CHOS-, CHOP- and CHONP-based molecules showed moderate inhibition. Dissolved organic matters (DOM) are widely present in different water sources, causing significant effects on water treatment processes. Herein, the molecular transformation behavior of DOM during peroxymonosulfate (PMS) activation by biochar for organic degradation in a secondary effluent were comprehensively analyzed. Evolution of DOM was identified and inhibition mechanisms to organic degradation were elucidated. DOM underwent oxidative decarbonization (e.g., –C2H2O, −C2H6, –CH2 and –CO2), dehydrogenation (–2H) and dehydration reactions by ·OH and SO4·−. N and S containing compounds witnessed deheteroatomisation (e.g., –NH, –NO2+H, –SO2, –SO3, –SH2), hydration (+H2O) and N/S oxidation reactions. Among DOM, CHO-, CHON-, CHOS-, CHOP- and CHONP-containing molecules showed moderate inhibition while condensed aromatic compounds and aminosugars exhibited strong and moderate inhibition effects on contaminant degradation. The fundamental information could provide references for the rational regulation of ROS composition and DOM conversion process in a PMS system. This in turn offered theoretical guidance to minimize the interference of DOM conversion intermediates on PMS activation and degradation of target pollutants.