Effectivity Optimization Of Low Temperature Sulfur Autotrophic Denitrification With Exogenous Electron Donor

With the rapid development of industry,the water environment in China is facing increasingly serious problems.Many groundwater and surface water have nitrate pollution problems.Excessive nitrate will not only lead to eutrophication of water,but also harm human health.At present,the mainstream denitrification technology is heterotrophic denitrification,but this technology needs to add a large number of carbon sources,the sludge output is large,the effluent COD is difficult to reach the standard,there are limitations;In contrast,sulfur autotrophic denitrification technology has the characteristics of no additional carbon source,no secondary pollution,less sludge yield,low operating cost,and various valence states and forms of reduced sulfur used for autotrophic denitrification,making it one of the preferred processes for the treatment of nitrogen-containing wastewater^[1-2].In this paper,elicit sulfur as electron donor,sulfur autotrophic denitrification technology combined with biological filter,deep denitrification treatment of NO₃-N pollution degree is relatively low wastewater,explore the low temperature conditions on the influence of sulfur autotrophic denitrification technology,and with the help of exogenous electron donor to strengthen the deep denitrification performance.The research results are expected to provide technical reference for practical engineering.First,the empty bed residence time（EBCT）was adjusted at the start-up stage of the reactor for 5 h,1 h and 0.5 h,respectively.The removal effects of nitrate and total nitrogen under various reaction conditions were measured,and the EBCT of subsequent tests was determined to be 0.5 h.The test temperature gradients of 12℃,15℃,20℃and 30℃were designed to control EBCT=0.5 h to explore the effects of different temperatures on the removal efficiency of nitrate and total nitrogen and the accumulation of nitrite in the sulfur autotrophic denitrification filter.The results showed that at 12℃,15℃,20℃and 30℃,the average nitrate removal capacity was 1.03 mg/L,2 mg/L,3.97 mg/L,12.32 mg/L,respectively.The low temperature inhibited the growth of sulfur autotrophic denitrifying microorganisms,thus reducing the denitrification efficiency.Secondly,in view of the low operating efficiency of the autotrophic denitrification filter at low temperature,Na₂S₂O₃·5H₂O was added as an exogenous electron donor to improve the denitrification performance of the reactor.The experimental results show that the addition of Na₂S₂O₃ contributes to the denitrification at low temperature,and the effect is the most obvious at 20℃.The average removal of nitrate is 6.95mg/L more than that before adding Na₂S₂O₃,but the accumulation of nitrite is also increased after adding Na₂S₂O₃.Finally,the microorganism on the surface of sulfur particles in the reactor was observed by SEM.It was found that there were more rod-shaped microorganism in the reactor,and a small amount of globular bacteria and helicobacter existed.Molecular biological analysis of microorganisms in the surface sludge of sulfur particles in the Na₂S₂O₃·5H₂O reactor was carried out.It was found that the relative abundance of denitrification-related microorganisms in the reactor increased under the condition of adding,and the relative abundance of Thiobacillus was the highest,with an average of 16.27%.In general,the relative abundance of bacteria associated with sulfur autotrophic denitrification in the dosing reactor increased.