Effect Of Biochar Structure On Hydrogen Sulfide Release During Aerobic Fermentation Of Municipal Sludge

Biochar,with its well-developed pore structure,huge specific surface and cheap and easy availability,has received wide attention in reducing the release of hydrogen sulfide（H₂S）during aerobic fermentation of municipal sludge.At present,most studies on the reduction of H₂S from biochar in aerobic fermentation have focused on the type and addition of biochar,but there is a lack of research on the effect of biochar structure on the release of H₂S from aerobic fermentation.Therefore,starting from the structure of biochar（specific surface area,the pore diameter and pore volume）,this paper explores the influence of biochar structure on the release of H₂S during aerobic fermentation,and analyzes the adsorption and transformation mechanism of H₂S by biochar through the characterization of biochar before and after aerobic fermentation.The relationship between the evolution of biochar structure and microbial community on H₂S release was discussed,and the mechanism of the influence of the biochar structure on H₂S release during aerobic fermentation was revealed.The main results are as follows.（1）The analysis of specific surface area and porous structure of biochar showed that the specific surface area and pore volume of biochar were:rice husk biochar>beech wood biochar>corn cob biochar;combined with the analysis of surface morphology,it was found that corn cob biochar had the largest pore size of 35.40 nm,and the pore diameter of beech wood biochar was more uniform.Three different structures of biochar were used as additives for aerobic fermentation experiments,namely,control group（CK）,corn cob biochar group（CBC）,beech wood biochar group（WBC）and rice husk biochar group（RBC）.The addition of biochar with smaller pore diameter during aerobic fermentation was more conducive to the heating of the pile,with the highest temperature reaching 72.60°C in the WBC group and 70.93°C in the RBC group.And the seed germination index of all treatment groups was greater than 100%,and it can be considered that all aerobic fermentation treatment groups reached decay.（2）Compared to the CK treatment,the cumulative H₂S release was reduced by 13.64%,50.00%and 36.36%in the CBC,WBC and RBC treatment groups,respectively.The correlation analysis between H₂S and the physicochemical properties of the piles showed that the main environmental factor affecting H₂S release was temperature.Using SEM-EDS,XRD and FTIR analysis means,it is known that the oxygen/sulfur（O/S）values of rice husk biochar decreased most significantly at the end of aerobic fermentation,indicating that rice husk biochar could adsorb the generated H₂S through-OH and-COOH functional groups and convert them into S⁰/SO₄^2-.（3）Based on the results of 16S r RNA high-throughput sequencing technology,it is known that the addition of biochar can improve the pile environment and increase the microbial abundance in the high temperature period,and the addition of biochar can alleviate the inhibition of sulfur-oxidizing bacteria（SOB）in the high temperature environment to reduce H₂S production.In addition,the WBC group could also inhibit the abundance of Desulfitibacter and Hydrogenispora to reduce H₂S production,and therefore,their cumulative H₂S release was the lowest.（4）Based on the RDA analysis,it was found that the pore diameter of biochar was negatively correlated with H₂S release,and biochar with smaller pore diameter was more favorable to reduce H₂S production;meanwhile,the larger pore volume of biochar was more favorable to the formation of aerobic zone in the pile,thus reducing H₂S production;the effect of biochar structure on H₂S release mainly depended on total pore volume(V_Total),followed by specific surface area(S _BET)and average pore diameter（D_P）.