Study On The Mechanism Of Autotrophic Desulfurization And Denitrification Treatment Of Sulfur-containing Waste Gas

Sulfur exhaust is a colorless and irritating toxic acidic gas,divided into inorganic sulfur exhaust and organic sulfur exhaust,mainly from industry and agriculture,which is released into the air untreated,causing harm to humans and the environment,such as dizziness,nausea,coma,and the formation of acid rain leading to building corrosion.Nitrates in water can lead to diseases and even cancer.The existing physicochemical methods such as absorption and catalytic oxidation to treat sulfurous waste gas and nitrate have the disadvantages of high operational and economic costs,secondary pollution or low load.Therefore,lower cost biological methods are widely used,among which the sulfide-denitrification process is studied as well as used because it can simultaneously treat nitrogen and sulfur removal.In this study,an anaerobic bioreactor treating sulfur-containing waste gas will be studied to remove sulfur-containing waste gas and nitrate simultaneously by wet process of sulfide-denitrification and denitrification technology under neutral conditions.The objective is to reduce secondary pollution,reduce operating costs and treat waste with waste.The study is as follows:The initial domesticated sludge was connected to a 3 L SBR-type reactor,and the nitrogen and sulfur removal characteristics of the reactor were investigated during the start-up phase by controlling the sulfide and nitrate influent loads and developing the reactor's tolerance to sulfide toxicity.During startup,the reactor temperature was controlled at 25-30°C,p H was 6.5-7.5,and the rotational speed was 100 rpm.after 35 d of startup,the removal of sulfide from the reactor was 99.8%and the removal of nitrate was 90.6%.The removal load was increased to 4.6 mmol/d for sulfide and 1.7 mmol/d for nitrate,and the S/N ratio removed was 2.7,which was not consistent with the reaction stoichiometry and presumably dissolved oxygen was involved in the reaction.The relative abundance of the major desulfurizing bacteria genus(Thiobacillus)was elevated from 7.5%to 39.5%,and it was tentatively concluded that the autotrophic desulfurization denitrification reactor was started successfully.H₂S was used to simulate the inorganic sulfur-containing waste gas instead of sulfide passages into the reactor during the start-up phase.The molar ratio of hydrogen sulfide as well as nitrate in the reactor,i.e.,S/N,was changed by controlling the hydrogen sulfide load as well as the nitrate load,and the sulfide-denitrification reactor with different S/N ratios and the types of products were investigated by gradually increasing the hydrogen sulfide load.At this stage,the final removal efficiency of nitrate was 99.8%and the final removal efficiency of hydrogen sulfide was 99.9%.The final hydrogen sulfide load was up to 4.5 mmol/d.At a nitrate load of 0.99 mmol/d,a hydrogen sulfide load of 3.26 mmol/d,and an S/N ratio of 3.3,the monomersulfur had a maximum yield of 62.6%,which was not consistent with the reaction stoichiometry at this stage,probably because dissolved oxygen was involved in the reaction and contributed to the nitrate removal.The autotrophic denitrification activity at this stage was 81?mol/gprot d.The relative abundance of the main genus Thiobacillus was up to78.2%at this stage.Compared with MBBR-type autotrophic desulfurization denitrification reactors,SBR-type reactors can withstand higher S/N ratios and are more suitable as a way to study the operation of autotrophic desulfurization denitrification systems for treating sulfur-containing waste gases at different S/N ratios.CS₂ was used to simulate organic sulfur-containing waste gas instead of inorganic sulfur-containing waste gas into the reactor.The molar ratio of CS₂ and nitrate in the reactor,i.e.,C/S/N,was also changed by controlling the CS₂ load as well as the nitrate load,and the nitrogen and sulfur removal and product types of the reactor under different C/S/N ratios were investigated by gradually increasing the CS₂ load.Also,in order to simulate the oxygen content that may exist in the actual project operation,oxygen was introduced into the reactor after 5 d of reactor operation.In the fully anaerobic stage,the nitrate removal efficiency was100%and the CS₂ removal rate was 92.9%.The nitrate removal efficiency decreased to 59.2%after the introduction of oxygen and increased to 92.1%in the next stage.Oxygen preferentially becomes an electron acceptor.Denitrification activity was inhibited by CS₂toxicity and the removal load was only 0.6 mmol/d in the final stage.The final removal rate of CS₂ was 99.0%with a removal load of 2.3 mmol/d.The sludge autotrophic denitrification rate at this stage was 230.8?mol/gprot?d,which was an increase over the denitrification rate at the inorganic sulfur-containing stage of the treatment.At an S/N ratio of 3.3,monomeric sulfur had a maximum yield of 75.6%and the effluent sulfate was stable.Under the combined effect of CS₂ and oxygen,the relative abundance of the main sulfur-oxidizing bacteria genus Thiobacillus decreased to 19.9%,while the relative abundance of the sulfur-oxidizing bacteria genus Chryseobacterium increased from 0 to 33.8%.Chryseobacterium replaced Thiobacillus as the main genus for sulfur oxidation at this stageThe SBR autotrophic sulfide-denitrification process studied in this experiment can remove sulfur-containing waste gas efficiently and stably,and proposed to have more sulfide-denitrification products at the same S/N ratio of 3.3.Compared with biofilter,it can withstand higher load of sulfur-containing waste gas.This process has lower organic matter consumption and lower operating cost.Based on this study,it is believed that if further expansion of the culture of the ₂ system can be carried out to realize the real treatment of sulfur-containing waste gas in biogas or other industries,it will not only promote the research on the treatment of sulfur-containing waste gas by the sulfide-denitrification system,but also deal with the research development of the biological treatment process for malodorous gases.