Sorption properties of greenwaste biochar for two triazine pesticides

Biochar is a carbon-rich product generated from biomass through pyrolysis. This study evaluated the ability of an unmodified biochar to sorb two triazine pesticides - atrazine and simazine, and thereby explored potential environmental values of biochar on mitigating pesticide pollution in agricultural production and removing contaminants from wastewater. A greenwaste biochar was produced by heating waste biomass under the oxygen-limited condition at 450°C. The effects of several experimental parameters, including biochar particle size, contact time, solid/solution ratio, and solution pH on the sorption of atrazine and simazine were comprehensively investigated. The biochar with small particle size needed less time to reach sorption equilibrium. The sorption affinity of the biochar for the two pesticides increased with decreasing solid/solution ratio. The sorbed amounts (C_s) of atrazine and simazine increased from 451 to 1158mg/kg and 243 to 1066mg/kg, respectively, when the solid/solution ratio decreased from 1:50 to 1:1000 (g/mL). The sorption of the biochar for both pesticides was favored by low pH. The sorption isotherms of atrazine and simazine on the biochar are nonlinear and follow a Freundlich model. When atrazine and simazine co-existed, a competitive sorption occurred between these two pesticides on the biochar, reflecting a decrease in sorption capacity (K_f) from 435 to 286 for atrazine and from 514 to 212 for simazine. Combined adsorption and partition mechanisms well depicted sorption of atrazine and simazine on carbonized and noncarbonized fractions of the biochar in the single-solute and co-solute systems.