The influencing mechanism of O_(2),H_(2)O,and CO_(2)on the H_(2)S removal of food waste digestate-derived biochar with abundant minerals

Hydrogen sulfide(H_(2)S)removal has been a significant concern in various industries.In this study,food waste diges-tate-derived biochar(DFW-BC),a by-product of food waste treatment with abundant minerals,was assessed for removing H_(2)S from different simulated biogas containing oxygen(O_(2))and carbon dioxide(CO_(2))and under differ-ent moisture(H_(2)O)contents(0%and 20%)of biochar.The influencing mechanisms of the gas conditions combined with the moisture contents were also investigated.The results showed an H_(2)S removal of 1.75 mg g^(−1)for dry bio-char under pure H_(2)S,4.29 mg g^(−1)for dry biochar under H_(2)S+O_(2),5.29 mg g^(−1)for humid biochar under H_(2)S,and 12.50 mg g^(−1)for humid biochar under H_(2)S+O_(2).For dry DFW-BC,the high Fe content was responsible for the O_(2)enhancement.In contrast,O_(2)+H_(2)O activated the catalytic H_(2)S oxidation of the less reactive minerals(mainly Ca).The inhibition of CO_(2)on H_(2)S adsorption was not obvious for dry DFW-BC;the specific pore structure may have provided a buffer against the physisorption competition of CO_(2).However,when H_(2)O was present on DFW-BC,the changes in critical biochar properties and sulfur speciation as opposed to that without H_(2)O implied an evident occurrence of CO_(2)chemisorption.This CO_(2)chemisorption partially hindered O_(2)+H_(2)O enhancement,decreasing the H_(2)S removal capacity from 12.50 to 8.88 mg g^(−1).The negative effect was ascribed to mineral carbonation of CO_(2),neutralizing the alkaline surface and immobilizing metal oxides,which thus reduced the acceleration in H_(2)S dissociation and activa-tion in catalytic H_(2)S oxidation by O_(2)+H_(2)O.