Mechanism Of Elemental Sulfur Production In Desulfurization And Denitrification Process Of Wastewater

A large amount of sulfur-nitrogen-containing wastewater discharged from petroleum,chemical,pharmaceutical and other industries has caused serious.harm to the surrounding environment and human health.The desulfurization-denitrification process has attracted much attention because it can simultaneously remove the three pollutants of carbon,nitrogen and sulfur,and it’s reaction products have no secondary pollution.However,in reality,there are some problems that need to be solved,urgently.The conversion of pollutants is unclear,which results in low production of elemental sulfur(S0),and it is difficult to quantify S0.This work focuses on the operation and regulation of the desulfurization-denitrification process,examines the effects of S/N and reflux ratio on the desulfurization-denitrification system,respectively,and analyzes the characteristics of the bacterial community structure of suspended and attached microorganisms in the system,and comes up with the migration and transformation mechanisms of sulfur.This work also analyzes the effect of different fillers and membrane hanging methods on the film hanging rates and output of S0 in the biofilm reactor;proposes a method for quick start and stable operation of the desulfurization-denitrification process;establishles the detection methods of S0 and polysulfide(Sn2-);basing on the spatial distribution characteristics of functional bacteria in the system,explores the metabolic pathway of sulfur,which is used to guide the improvement the generation of S0 in process.The main conclusions are as follows:(1)With the increase of S/N,the yield of S0 in the desulfurization-denitrification process gradually increases,the best S/N of autotrophic system and mixotrophic system are 3.5 and 3.67,respectively,at this time,the highest theoretical yield of S0 is 60%and 50%,respectively.The higher concentration of S2-has little effect on the removal rate of NO2-in the desulfurization-denitrification process,and the highest S2-concentrations in the autotrophic system and mixotrophic system,are 470mgS/L and 460mgS/L,respectively.When the S/N is lower,S0 is mainly generated by Sulfurovum’s autotrophic-desulfurization-denitrification reaction in suspended sludge.When the S/N is higher,S0 is mainly generated by Thauera’s mixotrophic desulfurization-denitrification reaction in attached-growth sludge.(2)With the increase of reflux ratio from 0.5 to 1.5,the yield of S0 in the desulfurization-denitrification process gradually increased,and the best reflux ratios of both two systems are the same as 1.5,and the highest theoretical yields of S0 are 20%and 50%,respectively.When the reflux is relatively low,the S0 generation efficiencies of the two systems are low,and the S0 is mainly distributed in the suspended activated sludge.When the reflux ratio is relatively high,the S0 generation efficiencies of the two system is high,and S0 can flow out with the effluent,which is convenient for recycling.(3)In desulfurization-denitrification systems,there are differences between suspended microorganisms and attached-growth microorganisms,and there are also differences among the microorganisms attached to the fillers at different locations.The top three dominant phyla in the autotrophic and mixotrophic systems are the same,which are Epsilonbacteraeota,Proteobacteria and Chloroflexi.The dominant genus with the highest abundance in both autotrophic and mixotrophic systems is Sulfurovum.Sulfurovum is mainly distributed in the suspended sludge,which can use S2-as the electron donor and NO2-as the electron acceptor,produce S0,SO42-and N2 by the autotrophic-desulfurizatio-denitrification reaction.(4)Pre-aerobic method can achieve fast membrane hanging,by which biological membrane is homogeneous and stable.The theoretical yield of S0 in the desulfurization-denitrification system,which is started by the pre-aerobic membrane hanging method,is higher than that by the method of fast discharging sludge.Aerobic sludge is more suitable as the inoculation sludge for desulfurization-denitrification systems than digested sludge.Sponge filler is the best filler,which is convenient for the attachment and growth of microorganisms.And the biofilm reactor with sponges as fillers has the higher yield of S0.(5)By analyzing the material balance of all sulfur-containing substances in the system,the metabolic pathway of sulfur can be studied.With the bioaction of Sulfurovum,S2-and NO2-undergo a desulfurization-denitrification reaction to produce N2 and S0.Then,S0 reacts with S2-to produce Sn2-chemically.With the bioaction of Sulfurovum,Sn2-reacts with NO2-to produce N2 and SO42-.With the bioaction of sulfate-reducing bacteria,SO42-reacts with CH3COO-to produce S2-again,and S2-continues to participate in the desulfurization-denitrification reaction.S0 reacts with S2-quickly to genetate Sn2-,which is the main reason of the low yield of S0 in the desulfurization and denitrification process.