Characterization of pesticide sorption behaviour of slow pyrolysis biochars as low cost adsorbent for atrazine and imidacloprid removal.

Agri-wastes biochars viz. eucalyptus bark (EBBC), corn cob (CCBC), bamboo chips (BCBC), rice husk (RHBC) and rice straw (RSBC) and acid treated RSBC (T-RSBC), were characterized for their physico-chemical properties and sorption behaviour of atrazine and imidacloprid was studied. Kinetics study suggested that except atrazine adsorption on RSBC, which was best explained by the pseudo second order model, sorption of atrazine and imidacloprid on biochars was well explained by the modified Elovich model. Among the five normal biochars, the RSBC showed the maximum atrazine (37.5-70.7%) and imidacloprid (39.9-77.8%) sorption. The phosphoric acid treatment of RSBC further enhanced the sorption of both pesticides in T-RSBC. The Freundlich adsorption isotherms were highly nonlinear and percent adsorption decreased with increase in pesticide concentration in solution. Pesticide adsorption on biochars was affected by their aromaticity, polarity, pore diameter, pH and weak acid fraction. Thus, rice straw biochars have great potential for environmental implications and can be exploited as adsorbents for pesticide industry spewed waste water purification.