Nitrite Accumulation Mechanism And Engineering Control Strategy In Sulfur Autotrophic Denitrification

In response to the urgent need of my country’s sewage treatment plants for the deep reduction of nitrogenous pollutants,this study is based on the sulfur autotrophic denitrification deep denitrification technology,and innovatively proposes to solve the problem of nitrite accumulation in the denitrification process to improve the deep denitrification.Effectiveness,it is expected to solve the problems of high operating cost,high sludge yield,and the risk of secondary COD exceeding the existing heterotrophic denitrification filter,and provide strong technical support for promoting the implementation of special emission limit standards in environmentally sensitive areas.This study is based on the designed sulfur autotrophic denitrification filter,using the anaerobic activated sludge of Beijing Gaobeidian Sewage Treatment Plant as the inoculation sludge to explore the accumulation mechanism of nitrous acid that restricts the performance of total nitrogen removal in deep nitrogen removal,With the help of external electron donors to solve the problem of nitrous nitrogen accumulation,in order to strengthen the deep denitrification performance.The research content mainly includes the following aspects:First,based on the different empty bed contact time（EBCT）to explore the denitrification efficiency of the sulfur autotrophic denitrification filter at the start-up stage,the EBCT was set to 5 h,1 h,0.5 h and 0.25 h,respectively,to determine the sulfur autotrophic denitrification filter The removal efficiency of nitrate nitrogen,total nitrogen removal efficiency,nitrite accumulation,dissolved oxygen（DO）,p H and alkalinity of the tank under different EBCT conditions,and the denitrification performance of the filter is obtained as the EBCT decreases At the same time,the nitrite accumulation mechanism is also explored,that is,the increase of the influent load of nitrate nitrogen makes the nitrate nitrogen removal load further increase,which in turn causes the accumulation of nitrite.The accumulation of nitrite is the main reason that limits the removal effect of total nitrogen.When the EBCT was 0.25h,the average accumulation concentration of nitrite was 1.84 mg/L,the average total nitrogen in the influent was 16.54 mg/L,and the average total nitrogen in the effluent was 9.13 mg/L.Later,in view of the problem of nitrite accumulation in the sulfur autotrophic denitrification filter under lower EBCT conditions,which would affect the total nitrogen removal efficiency,the addition of an external electron donor（Na₂S₂O₃·5H₂O）was used to increase the sulfur autotrophic reaction.The utilization efficiency of nitrifying microorganisms on sulfur sources solves the problem of nitrous acid accumulation and further improves the denitrification efficiency of the sulfur autotrophic denitrification filter.The experiment shows that with the increase of the amount of external electron donor,the removal effect of total nitrogen is strengthened.When no external electron donor was added,the total nitrogen in the effluent of the sulfur autotrophic denitrification filter in this experiment was lower than the standard of 10 mg/L.When the concentration of the chemical was 33.40mg/L,the total nitrogen concentration in the effluent was low At the 5 mg/L standard,when the dosing concentration is 66.80 mg/L,the total nitrogen concentration in the effluent is lower than the 2 mg/L standard.Among them,the relative abundance of Proteobacteria and Thiobacillus in the sulfur autotrophic denitrification reactor is the highest.Thiobacillus plays a major role in the process of sulfur autotrophic denitrification and denitrification.