Sorption mechanisms of pesticides removal from effluent matrix using biochar: Conclusions from molecular modelling studies validated by single-, binary and ternary solute experiments

Abstract

Sorption of atrazine (ATZ), imidacloprid (IMIDA) and azoxystrobin (AZOXY) in single-, bi- and ternary-solutes system was modelled using phosphoric acid-treated rice straw biochar (T-RSBC). The T-RSBC showed stronger sorption capacity for IMIDA in single- and bi-solute systems. The Freundlich constant (KFads) in ternary system followed the order: ATZ (222.7) < IMIDA (1314) < AZOXY (1459). Adsorption modeling and molecular dynamics suggested that non-bonding interactions between aromatic groups and electrostatic interactions with the phosphate ester group in T-RSBC played an important role. Enhanced sorption by pore-filling may be attributed to the stacking of pesticide molecules in the form of multilayer. IMIDA was predominantly sorbed by pore-filling mechanism, whereas, ATZ adsorbed by partitioning mechanism. The percent removal of three pesticides in waste water effluent followed the order: AZOXY > IMIDA > ATZ. The Freundlich isotherm based multicomponent Sheindorf-Rebuhn-Sheintuch equation's suggested that the extent of ATZ adsorption, in the presence of co-habiting pesticides, decreased with increase in number of solutes (KiATZ, Singlev> KiATZ, Binary> KiATZ, Ternary). The competitive coefficient values (αATZ/IMIDA, Ternary > αATZ/AZOXY,Ternary) revealed that ATZ adsorption in ternary system was inhibited more by the presence of IMIDA than AZOXY. Findings suggested that biochar with a large fraction of non-carbonized phase promoted non-competitive sorption.