Bioconversion Of Sulfate And Nitrate In Scrubbing Liquor Of Chemical Absorption-Biological Treatment Intergrated Flue Gas Simultaneous Desulfurization And Denitration Process

With the increasingly serious air pollution, flue gas desulphurization and denitration have become one of the main ways to control air pollution. Although the current physical-chemical flue gas desulphurization and denitration technologies can successfully remove pollutants from flue gas, they all have issues with high operation costs, complex process and secondary pollution generation to different degrees. Therefore, researchers have been working on developing more efficient and more economical flue gas desulphurization and denitration processes. In order to realize the complete innocuity and resource utilization of sulfur dioxide ?SO₂? and nitric oxides ?NOX? in flue gas, biological desulphurization and denitration process have won more and more attention, because of its high efficiency, low cost, no secondary pollution and etc.In light of previous researches on biological flue gas desulfurization ?BIO-FGD?, Oxidation-absorption flue gas denitration and aerobic denitrification, the dissertation puts forward a chemical absorption-biological treatment intergrated flue gas simultaneous desulfurization and denitration process, in which first transfers SO₂ and NO_x to the aqueous phase by chemical absorption and then achieves the complete innocuity and resource utilization of SO₂ and NO_x in the aqueous phase by biological conversion. The process flow are as follows:Firstly, SO₂ and NOX in flue gas were separately absorbed in two absorption tower, in which SO₂ was converted to sulfate and sulfite by alkaline absorbent and NOX was oxidized to nitrate and nitrite by oxidant and alkaline absorbent. And then, the generated sulfate and sulfite was reduced to sulfide by sulfate reducing bacteria ?SRB? in anaerobic bioreactors. At last, the effluent containing sulfide and the flow containing nitrate and nitrite run into one microaerobic bioreactor, where sulfide was oxidized to sulfur and nitrate or nitrite was reduced to N2 by the interactions of Sulfur-oxidizing bacteria ?SOB?, Nitrate-reducing, Sulfide-oxidizing bacteria ?NR-SOB? and Nitrate-reducing bacteria ?NRB?, aiming at simultaneous removal of SO₂ and NO_x from flue gas with high sulfur production efficiency and the regeneration of alkaline absorbent.The key step in the chemical absorption-biological treatment intergrated flue gas simultaneous desulfurization and denitration process mentioned above is the biological conversion process of SO42- and NO3-, which determines the resource utilization and harmlessness of SO₂ and NO_x in flue gas. Concerning this issue, the dissertation focused on studying the sulfate and sulfite reduction process in anaerobic bioreactor as well as the sulfide oxidation, nitrate reduction and sulfur generation process in microaerobic bioreactor. At first, sulfate reducaion process was explored in anaerobic bioreactor using glucose as carbon source and sulfite reducing was studied process in anaerobic bioreactor introduced with waste activated sludge ?WAS? lysate liquid as carbon source. And then, the effects of DO, influent load and carbon source on sulfide oxidation, nitrate reduction and sulfur generation were investigated in microaerobic bioreactor. Afterwards, the transformation mechanisms involved in organic degradation, sulfide oxidation and nitrate reduction were deduced under microaerobic conditions. The dissertation was intended to provide a theoretical basis and technical support for the industrial application of chemical absorption-biological treatment intergrated flue gas simultaneous desulfurization and denitration process. The main results were as follows:In the sulfate-reducing anaerobic bioreactor, the performance of converting sulfate to sulfide was investigated with glucose as carbon source. The results showed that both the sulfate conversion efficiency and the sulfide generation efficiency could reach about 85% with the sulfate load increased to 2.74 kg SO42-/m³/d ?SO42-S,0.89 kg S/m³/d?. However, the addition of glucose would increase the substrate cost. In the mean time, WAS contains a lot of organic matter that can also be used as carbon source by microorganisms. In order to decreased desulfurization cost, the performance of converting sulfite to sulfide was investigated with WAS lysate liquid as carbon source in sulfite-reducing anaerobic bioreactor. At the optimum COD/SO32-= 3:2, both the sulfate conversion efficiency and the sulfide generation efficiency can reach about 80% with the influent load ?SO32--S? as high as 3.55 kg S/m³/d.In the microaerobic simultaneous sulfide oxidation ?S2-?>S0? and nitrate reduction ?NO3-?N2? bioreactor, the effects of dissolved oxygen ?DO? on the bioreactor operation performance were evaluated with glucose as carbon source. The results showed that the optimum DO was 0.1-0.3 mg/L. Under the optimum DO conditions, when the sulfide load increased to 8.16 kg S/m³/d, both the sulfide conversion efficiency and the sulfur generation efficiency reached 99% or more. At the same time, the nitrate load reached 2.48 kg N/m³/d with nitrate removal efficiency approaching 90%.In the glucose-supplied microaerobic simultaneous sulfide oxidation?S2-?S0? and nitrate reduction bioreactor ?NO3-?N2?, when the influent load was maintained at 8.72 kg S/m³/d and 2.49 kg N/m³/d, the effects of DO on the microbial diversity, the community structure and the abundance of functional bacteria were explored by PCR-DGGE. It was revealed that sulfide conversion efficiency, nitrate removal efficiency and sulfur generation efficiency reached a maximum at 0.1-0.3 mg DO/L. Correspondingly, SOB and NRB also had the highest abundance at 0.1-0.3 mg DO/L. However, when the DO was further elevated to more than 0.5 mg/L, the abundance of NRB were markedly decreased, while the abundance of carbon degradation species were increased with increasing DO. Metabolic mechanisms involved in microaerobic sulfide and nitrate conversions processes at the optimal DO range were deduced based on the combination of the results of batch tests, the characteristics of microaerobic bioreactor and the analyses of functional microorganisms. It showed that the oxidation of sulfide to sulfur was mainly performed by heterotrophic SOB and autotrophic NR-SOB, while the reduction of nitrate to N2 is mainly completed by autotrophic NR-SOB and heterotrophic NRB. In addition, the conversion of nitrite ?an intermediate product? to N2 was mainly realized via heterotrophic NRB.In the microaerobic simultaneous sulfide oxidation ?S2-?S0? and nitrate reduction ?NO3-?N2? bioreactor, the feasibility of using WAS fermentation liquid instead of glucose as carbon and energy source for the treatment of sulfide and nitrate were investigated, accompanied by the analyses of the processes characteristics. When the influent load of sulfide and nitrate was increased to 8.52 kg S/m³/d and 2.53 kg N/m³/d, both the sulfide conversion efficiency and the sulfur generation efficiency reached 99% or more and the nitrate removal efficiency reached 95% or more. The results of batch experiments showed that with WAS fermentation liquid as carbon source, the bioconversion efficiency of sulfide and nitrate were higher than that with the addition of glucose.