Microaerobic In-situ Removal Of Hydrogen Sulfide And Sulfur Conversion During Biogas Fermentation Process

In the current energy context,the possibility of generating heat and electricity from biogas are attractive reasons for application of anaerobic digestion to treat biomass wastes.H₂S is typically the main pollutant in the biogas with concentrations ranging from 12 to 1 g/m³ and would cause heavy corrosion problems in the pipeline and installations for energy recovery.So desulfurization is very important for the efficient utilization of biogas.The current commercial technologies for H₂S removal such as dry adsorption,wet absorption or biological desulfurization are usually postpositional.Nowadays the exploratory research reports about in-situ desulfurization under micro-oxygen condition have attracted people's attention.Mixture of straw and manure were used as fermentation substrate to produce biogas by anaerobic batch fermentation operating under mesophilic condition?35�1??.A certain amount of oxygen was introduced into the anaerobic fermentation device for removal of H₂S.The removal efficiencies were investigated under oxygen content(3.95 L/m³_biogas,7.90 L/m³_biogas,11.85 L/m³_biogas)and oxygen providing frequencies?1 time/d,2 times/d,3 times/d?.Elemental sulfur content in fermentation liquor before and after biogas generation,H₂S production,sulfate concentration in biogas collecting bottle were measured to speculate the conversion of sulfur during the process.The abundance of microbial communities in anaerobic system was analized by high throughput sequencing to explain the influences of oxygen addition.Last,the effect of pretreatment for straw was tested and discussed.The results show:When oxygen introduced at 3.95 L/m³_biogas,7.90 L/m³_biogas or11.85 L/m³_biogas into the fermentation system,the daily biogas production and cumulative production changed non-significantly and the methane production increased slightly.While the dosage of oxygen increased,the cumulative gas production decreased about 10%,but methane production increased slightly.The corresponding average removal efficiency were 70%,90%and 91%,respectively.With the increase of the amount of oxygen,the removal efficiencies of H₂S increased and reached the level about 90%.The introduction of oxygen inevitably leads to increase the content of residual oxygen which could be controlled below 0.5%,in accordance with the relevant standards.Under oxygen supply of 11.85L/m³ _biogas,daily production and cumulative gas production were effected by the oxygen providing frequency.With the increase of the oxygen providing frequency,the cumulative biogas production decreased and the gas production peak postponed.However the cumulative methane production changed unconspicuously.While the oxygen providing frequency increased,the removal efficiencies increased.And at the same time the content of residual oxygen increased but it could still be controlled below 0.5%and meet the requirement of relevant standard.The sulfur content of straw and pig manure?as biogas feedstock?as well as biogas slurry were 0.123%,0.530%and 0.029%,respectively.Pig manure is a major source of sulfur in raw materials,accounting for 91.9%.During the fermentation process,most of sulfur in the raw materials?about 65%?were converted into H₂S.Under the experimental conditions,about 70⁹1%of H₂S in biogas were oxidized and removed.The main product were sulfur?about 80%?and a small amount of sulfate.Sulfur is mainly retained in the fermentation bottle,sulfate was detected in gas collecting bottle.The high-throughput sequencing analysis shows that the diversity of microbial communities increases and the correlation weakened with the increase of oxygen introduced into anaerobic system.Sulphide-oxidizing bacteria increase while the methanogens change indistinctively with the increase of oxygen.And the higher concentration of sulphide-oxidizing bacteria could convert the H₂S in biogas timely,Which reduce the inhibitory effect on the activity of methanogens and increase the methane production.