Competitive Interactions of NH3 and Toluene with Biochar Modified by Pre- and Post-Treatments of H3PO4 in Dual Adsorption Systems

Abstract

Biochar modified by H₃PO₄ treatment can be used to purify malodorous gases during bio-drying of sludge, but the current understanding of multi-component adsorption of malodorous gases through biochar is limited. This study examined the adsorption mechanism of mixed malodorous gases including toluene and ammonia (NH₃) on two kinds of biochar modified via H₃PO₄ pretreatment before and after pyrolysis. The biochar obtained by H₃PO₄ pretreatment of biomass before pyrolysis (C550) preferred to adsorb NH₃ whether in the single or the dual system. In contrast, the biochar obtained by H₃PO₄ reprocessing after pyrolysis of biomass (C350-550) tended to adsorb toluene in the dual system but was more efficient in absorbing NH₃ in the single system. The pseudo-second-order kinetic model indicated the synergistic adsorption between NH₃ and toluene for all biochar samples. In-situ DRIFTS of C350-550 during adsorption demonstrated the formation of amino functional groups caused by NH₃ chemical adsorption with -OH (or -COOH) in the dual system. These increases in basic groups on C350-550 could enhance the surface zero potential point of C350-550, thereby improving the non-polarity of C350-550 and benefit the adsorption of weak polar toluene.