Determination of Instinct Components of Biomass on the Generation of Persistent Free Radicals (PFRs) as Critical Redox Sites in Pyrogenic Chars for Persulfate Activation

Persulfate (PS) activation on biochar (BC) is a promising technology for degrading the aqueous organic contaminants. However, the complexity of activation mechanisms and components in biomass that used to produce BC makes it difficult to predict the performance of PS activation. In this study, we employed eight sludges as the representative biomass that contained absolutely different organic or inorganic components. Results showed that the elemental composition, surface properties, and structures of the sludge-derived BCs (SBCs) clearly depended on the inherent components in the sludges. The intensities of persistent free radicals (PFRs) in the electron paramagnetic resonance (EPR) correlated positively with N-containing content of sludges as electron shuttle, but negatively with the metal content as electron acceptor. Linking with PFRs as crucial sites of triggering a radical reaction, a poly-parameter relationship of predicting PS activation for organic degradation using the sludge components was established (k_obs,PN = 0.004 × C_protein + 0.16 × C_M^-0.895 -0.118). However, for the PS activation on those SBCs without PFRs, this redox process only relied on the sorption or conductivity-related characteristics, not correlating with the content of intrinsic components in biomass but with pyrolysis temperatures. This study provided insightful information of predicting the remediation efficiency of PS activation on BCs and further understanding the fate of contaminants and stoichiometric efficiency of oxidants in a field application.