Study On The Performance Of Biogas Desulfurization Coupling With Denitrification For The Treatment Of Domestic Sewage

Compared with physical and chemical method,traditional domestic sewage biological treatment technology has the advantages of low energy consumption and high efficiency,and has been widely used.However,the traditional process mainly relies on heterotrophic denitrification.Additional carbon source was needed,which greatly increased the operational cost.With the increase of COD concentration in effluent,sludge production and subsequent treatment costs were also higher.Additionally,the activity of heterotrophic denitrifying bacteria was inhibited by the presence of a small amount of dissolved oxygen in the reflux nitrifying solution.In this study,a biogas desulfurization coupling with denitrification for the treatment of domestic sewage system was constructed.The biogas produced by anaerobic digestion of sludge was introduced into a stable heterotrophic denitrification process.H₂S in biogas could be used as electronic donor for autotrophic denitrification,and a mixotrophic denitrification system was constructed.The effect of different hydraulic retention time and H₂S concentration on the efficiency of the process system were investigated.At the same time,the successional law of functional group of microorganisms under different operational parameters was analyzed,and the economic evaluation of the process system was carried out to clarify its application prospects.The process system consists of two units:?1?BD-IAHD unit?EGSB?,methanogens remove part of COD from wastewater,and autotrophic denitrifying bacteria use NO₃^-returned from AN unit as electron acceptor,oxidizing H₂S in biogas to sulfur and reducing NO₃^-to NO₂^-.Heterotrophic denitrifying bacteria use the remaining COD as carbon source and electron donor to reduce NO₂^-to N₂.?2?AN unit?BAF?,mainly produces nitrification.After the BD-IAHD unit and AN unit started up successfully and ran steadily,the effluent of the BD-IAHD unit was treated as the inflow of the AN unit.The effluent of the AN unit was refluxed to the BD-IAHD unit with a reflux ratio of 3:1.At this time,the HRT of the BD-IAHD unit was 12 hours and that of the AN unit was 4 hours.Under this condition,the removal rates of COD,NH₄⁺-N and TN of the process system were 78-80%,96-100%and 68-71%respectively.When HRT of the process system was cut down to 6+2h,the removal rates of COD,NH₄⁺-N and TN reached 72-74%,90-100%and 64-72%respectively.Because the removal rate of COD decreased slightly at this time,the HRT of the process system was adjusted to 6+4 h.The removal rates of COD,NH₄⁺-N and TN in the process system can reach 86-88%,96-100%and 64-72%respectively.The optimum HRT of the process system was determined to be 6+4 h.Under this condition,biogas was injected into the BD-IAHD unit.At the initial stage,the NH₄⁺-N concentration in the effluent of BD-IAHD unit rapidly increased to 15 mg/L,and the removal rate of TN decreased to 50%.After 10 days,the TN removal rate of the system recovered to 70%and gradually increased to 85%,and the effluent COD concentration of the process system also gradually decreased to 40mg/L.Reducing H₂S concentration in biogas to 1.2%and 0.9%has little effect on the operation efficiency of the process system.In addition,the concentration of H₂S in the outlet gas decreases to 0 mg/L,achieving the goal of biogas purification.High-throughput sequencing of activated sludge in different stages of BD-IAHD unit in the process system showed that the richness and diversity of microbial community were improved after biogas was introduced.The optimal phylum in BD-IAHD unit is Proteobacteria.Bacteroidetes,closely related to nitrogen removal,had an abundance of19%at 6h without biogas.After biogas with an H₂S content of 1.5%was introduced,its abundance decreased to 12.9%and gradually increased to 15%after the concentration of H₂S decreased.After the introduction of biogas,the abundance of Anaerolinea decreased from 4.64%to 1.54%,while the abundance of Bacteroides increased from 1.58%to4.47%.Anaerolinea has been replaced by Bacteroides.When the HRT of BD-IAHD unit is 6h and no biogas is applied,the abundance of Comamonas is 0.53%,after biogas was used,the abundance increased to 1.07%,and after H₂S concentration was reduced to 1.2%and 0.9%,the abundance was 0.66%and 0.84%,respectively.Pseudomonas's initial abundance was 0.15%when biogas was not turned on,and increased to 0.35%when HRT decreased to 6h.After the biogas with H₂S of 1.5%was injected,its abundance increased to 0.82%,and the concentration of H₂S subsequently decreased to 1.2%and 0.9%,with little change in its abundance?0.73%and 0.74%,respectively?.Based on the economic evaluation of the project,the investment and construction cost of the project is 1176.1 yuan/m³ per ton of water.Sewage treatment operation cost is 0.4766 yuan/m³,sludge treatment cost and purification biogas power generation income are converted into sewage treatment cost of 0.216 yuan/m³ and 0.133 yuan/m³respectively,the net operation cost can be calculated as 0.5596 yuan/m³.