Study On Granulation And Simultaneous Denitrification And Desulfurization Performance Of Sulfur Autotrophic Denitrifying Granular Sludge In Continuous Flow Mode

The problem of groundwater pollution is serious,and excessive discharge of sulfur-containing and nitrogen-containing wastewater will cause harm to the water environment and the human body.The denitrification and desulfurization processes currently used to treat nitrates and sulfides in water are generally carried out separately,which not only complicates the processing system but also increases the processing cost.Compared with traditional biological methods,autotrophic denitrification denitrification technology has become an important topic in the current water treatment industry due to its high efficiency,low consumption and no secondary pollution.When sulfide is used as an electron donor,sulfur autotrophic denitrification can be performed to achieve simultaneous nitrogen and sulfur removal.However,the microbial growth in the autotrophic reactor is slow,and the low yield leads to slower biomass growth,which will seriously affect the denitrification performance.Sludge granulation as an effective biomass retention technology can effectively solve this problem.The aim of this study was to use a laboratory-scale continuous flow reactor for the cultivation and domestication of sulfur autotrophic denitrifying granular sludge.The formation process and granulation mechanism of sulfur autotrophic denitrification granular sludge were investigated from the aspects of sludge morphology,physical and chemical properties,extracellular polymer secretion and microbial community.The mature sulfur autotrophic denitrifying granular sludge was used as inoculated sludge to study the effects of different hydraulic retention time and inorganic carbon source dosage on the stable operation of the reactor.The effects of simultaneous nitrogen and sulfur removal in the granular sludge reactor and the microbial community structure in the reactor under different working conditions were analyzed.This study can be used as a reference for long-term stable operation and high efficiency of sulfur autotrophic denitrifying granular sludge.The main conclusions are as follows:The inoculated sludge was taken from the biological tank of the common sewage plant,and the reactor was started in continuous flow mode.There was a circulating pump inside.Particles started to appear in the 15 th week,the granulation was completed at the 30 th week.The sulfur autotrophic denitrification granules can maintain good simultaneous nitrogen and sulfur removal efficiency during the startup process.Comparing the physical and chemical properties of the granular sludge inoculated with sludge,it was found that the composition of the sludge changed significantly,and elements such as calcium participated in and promoted the formation of granular sludge.The formation of sulfur autotrophic denitrifying granular sludge was a complicated process.The selective pressure was used to discharge a small amount of flocculent sludge,and the inorganic matter formed by calcium ions acted as the microbial core.The secretion of EPS increased the adhesion of small particles and promoted the accumulation of microorganisms to form regular-shaped,structurally stable sulfur autotrophic denitrifying granular sludge.High-throughput sequencing results showed that the microbial diversity in the sludge decreased during the start-up process,but the content of sulfur autotrophic denitrification-related genus increased continuously,and Sulfurovum(19.71%)and Thiobacillus(14.47%)acted as the most important functional bacteria that participate in the simultaneous denitrification and desulfurization process in the mature granular sludge.When the influent nitrate and sulfide concentrations were 36.38±3.2 and 112.46±12.84mg/L,respectively,as hydraulic retention time was reduced from 12 h to 2h,the effect of simultaneous nitrogen and sulfur removal was not greatly affected.Only at HRT=2h,the nitrogen removal efficiency of the system decreased slightly,but still maintained a removal rate of more than 95% for nitrates and sulfides,indicating that the sulfur autotrophic denitrification granular sludge can withstand the impact of volumetric load.The total amount of PN,PS or EPS in granular sludge EPS increased first and then decreased,indicating that excessive or too low hydraulic retention time was both not conducive to EPS secretion.3D-EEM analysis showed that the main fluorescent substances in EPS under different HRT was the same,both were dissolved organic matter and proteinaceous substances,which proveed that the particles can maintain the activity well.HRT has a selective effect on microbial community structure.The microbial diversity in granular sludge decreases with the decrease of HRT.In addition to the two main functional bacteria of Sulfurovum and Thiobacillus,some unclassified strains of Anaerolineaceae and Hyphomicrobiaceae were also contribute to the simultaneous denitrification and desulfurization process.The influent nitrate and sulfide concentrations were 37.05±3.12 and 95.28±19.78mg/L,respectively,under the different inorganic carbon source dosage,the removal rate of nitrate in the reactor can be maintained above 98%,but the removal rate of sulfide was first decreased and then increased.Different trends of remval efficiency indicate that there were other ways for the reactor to remove nitrate.Under the low inorganic carbon source,filamentous bacteria will be produced on the surface of the granular sludge,but after increasing the dosage of the inorganic carbon source,the regular and stable granular sludge morphology can be maintained,which was accompanied by the PS content Increase first and then decrease.Under the different inorganic carbon source dosages,the fluorescent substances of EPS were mainly dissolved organic matter and proteinaceous substances,and almost no humic acids and fulvic acids were detected,indicating that the granular sludge can be well maintained at different stages.The dosage of inorganic carbon source would affect the distribution of autotrophic bacteria,heterotrophic bacteria and facultative bacteria in the reactor.These microorganisms worked together to achieve simultaneous removal of nitrate and sulfide in the reactor.According to the sequencing results,Sulfurovum and Sulfurimonas were involved in the autotrophic denitrification process as a main functional bacterium,and contributes to the denitrification process together with autotrophic/heterotrophic bacteria with denitrification functions such as norank＿Rhodocyclaceae,Thauera,and norank＿Rhodobacteraceae.