Control Of H₂S In Anaerobic Digestion Of Slaughterhouse Sludge: Effects Of PH And Biochar Addition

Anaerobic digestion technology is widely used because of good sludge stabilization,relatively simple facilities and high energy product ion.Biogas produced by sludge anaerobic digestion is a renewable energy,which can be used to generate electricity and or as fuel for vehicles.Biogas contains a certain amount of hydrogen sulfide（H₂S）,which has a negative impact on the economic value of biogas.The content of H₂S in biogas ranges from 0.1 to 3%,the highest of which is even higher than the upper limit of biogas utilization equipment,which limits the direct utilization of sludge biogas.Therefore the biogas must be desulphurized before utilization,which not only greatly increases the operating costs but also seriously reduces the economic benefits of sludge anaerobic digestion.In addition,the presence of sulfide during anaerobic digestion inhibits methanogens activity,thereby affecting the methane production,even leading to failure of anaerobic digestion.At present,more and more attention is paid to controlling the H₂S generation during anaerobic digestion.In this paper,two strategy for minimizing H₂S generation and maximizing methane production were carried out during anaerobic digestion of slaughterhouse wastewater sludge at 35±1℃.The first was to investigate the effect of initial pH value on H₂S generation and methane production.The second was to explore the effect of adding rice husk biochar on H₂S generation and methane production.The main conclusions of dissertation are as follows:（1）When the initial sludge pH increased from 6.5 to 8.0,the biogas production increased by 10%,the methane production increased by 64%,the methane content in biogas increased by 48.6%,while the H₂S content in biogas decreased by 44.7%after 21-day sludge digestion.The higher initial sludge pH inhibited the competition of sulfate-reducing bacteria with methane-producing bacteria,and thus benefiting to the growth of methanogens.Positive correlations between the relative abundance of desulfomicrobium and H₂S production,as well as the Methanosarcina abundance and methane production were obsearved.Further,the initial sludge pH influenced the formation of H₂S by affecting the sulfate reduction and organic sulfur release.At a lower pH more sulfate and organic sulfur were transferred to H₂S,which was released into the gas phase.（2）With the optimal biochar dosage of 2 g/L,the cumulative biogas production increased 15.6%,the cumulative methane production increased 56.8%,the methane content in biogas increased by 36%,and the H₂S content in biogas decreased by34.1%,and the H₂S concentration finally droped below 163 mg/m³.With the increase of biochar addtion,both methane production and H₂S inhibition was weakened.When the biochar dosage increased to 14 g/L,the formation of H₂S was promoted and the methane production was inhibited.The biochar addition not only promoted electron transfer,but also enhanced the release of organic sulfur while adsorbing the generated H₂S.In this work,the control of initial sludge pH and the addition of rice husk biochar were found to have obvious impact on the H₂S generation and methane production during anaerobic digestion,which will provide some guidance and theoretical basis for controlling the H₂S production and promoting methane production during anaerobic digestion.