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 digestate-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 different 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 biochar 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 activation in catalytic H 2 S oxidation by O 2 + H 2 O. Graphical Abstract