Potential of Different Biochars for Glyphosate Removal in Water; Implications for Water Safety

Abstract

We investigated the potential of two different types of biochars (BCs), a waste by product from a Dendro bioenergy industry (DBC) and a steam activated rice husk derived biochar (SRBC) to remove glyphosate from aqueous media. Equilibrium isotherms and kinetics experiments were conducted to study the adsorption behaviour and postulate potential mechanisms. Glyphosate adsorption on both BCs was strongly pH dependent, exhibiting maximum on DBC and SRBC at 5-6 and 2-4 pH, respectively. Isotherm data obtained for DBC adsorption was best fitted to Freundlich and Temkin models indicating a multilayer adsorption, whereas glyphosate adsorption on SRBC was well described by Freundlich and Langmuir models suggesting both physisorption and chemisorption mechanisms for the adsorption process. The Langmuir maximum adsorption capacity of DBC and SRBC was 44.00 and 123.03 mg/g, respectively. The kinetics of glyphosate adsorption on DBC were best described by pseudosecond order mode indicating that the rate limiting step can possibly be a chemical adsorption, while pseudo-first order model described kinetics of glyphosate adsorption on SRBC indicating physisorption interactions for glyphosate adsorption. Pore diffusion, π*-π electron donor-acceptor interactions and H-bonding were postulated to be involved in physisorption, whereas electrophilic interactions led to chemisorption type of adsorption for both DBC and SRBC. Overall, both DBC and SRBC could be a promising remedy of glyphosate removal from aqueous solution.