Study On Nitrogen Removal Performance Of Low C/N Domestic Sewage Treated By Mn/Carbon Source

The accumulation of nitrogen-containing pollutants in water will cause eutrophication and water ecological environment problems.Biological nitrogen removal technology is widely used because of its high efficiency and low cost.However,the traditional biological denitrification process is affected by the supply of organic carbon source,and the denitrification effect is not ideal.As a solid-phase slow-release carbon source and biofilm carrier,loofah complex has the potential to improve denitrification and denitrification.As a common element in the earth’s crust,manganese oxide（MnOx）has adsorption and oxidation.The solid-phase carbon source based on manganese loading can catalyze the nitrification and denitrification process and improve the biological denitrification treatment of low C/N domestic sewage.In this experiment,a manganese loaded loofah complex filler was prepared,and a biofilter system was constructed to treat low C/N domestic sewage by simultaneous nitrification and denitrification（SND）.The effects of different C/N,do,HRT and temperature on denitrification were explored.In addition,the microbial community structure and gene function of different biofilters were studied by high-throughput sequencing and macrogenomic technology.The research results of this paper have certain guiding significance for the high-efficiency denitrification technology of low nitrogen wastewater.The research conclusions are as follows:（1）The concentration of potassium permanganate（KMnO₄）and reaction time will affect the nitrogen removal and carbon release capacity of towel gourd.With the increase of KMnO₄concentration and reaction time,the adsorption and removal rate of ammonia nitrogen by modified filler increased;The higher the concentration of KMnO₄,the stronger the carbon release capacity;The longer the reaction time,the weaker the carbon release ability.Static nitrification and denitrification experiments show that the modified filler can completely remove NH₄⁺-N within 48hours.During the nitrification process,the nitrate content increases and the nitrite accumulation first increases and then decreases;The complete removal of NO₃^--N can be achieved within 72hours,and the nitrite accumulation in the denitrification process does not exceed 0.4mg·L^-1.（2）The solid-phase carbon source biological filter system can achieve effective simultaneous nitrification and denitrification,and the ammonia nitrogen removal rate can reach about 50%and85%respectively in the start-up stage;when the influent C/N is 5,it can simultaneously satisfy the removal of NH₄⁺-N and total nitrogen.The addition of manganese oxide（MnO_x）can effectively improve the simultaneous nitrification and denitrification efficiency of the biological filter,so that the removal of NH₄⁺-N and total nitrogen can reach up to 98.76%and 78.47%;further,DO also has a great influence on the effect of SND.The removal effect of total nitrogen is the best when DO=4.0 mg·L^-1,and the TN concentration in the effluent of the two systems is lower than 10.In addition,with the change of HRT and temperature,the nitrogen content and composition of the effluent are different.The specific performance is that when HRT=12h,the TN of the effluent can meet the urban sewage treatment plant pollutant discharge standard（GB18919-2002）Class A standard,However,the NH₄⁺-N concentration in the effluent is high,and when HRT=18h,the TN removal rates of the two systems can reach 59.47%and 80.71%,respectively,and the average TN concentration in the effluent is 14.73 and 7.82,respectively.The effluent reaches the standard and the removal effect of pollutants is stable;the effect of temperature on the SND effect of the reactor is to promote the simultaneous nitrification and denitrification of the biological filter in summer,and inhibit the progress of nitrification and denitrification in winter.In the nitrification and denitrification series experiment stage at low temperature,the NH₄⁺-N concentration of the influent water is controlled to be about 20 mg·L^-1,and the NO₃^--N concentration is about 10 mg·L^-1.Under the condition that the C/N of the influent water is kept constant at 5,the nitrate nitrogen removal rate of the combined system can reach 92%.The highest removal rate can reach 99%,and the effluent quality can reach the Class A discharge standard of urban wastewater.（3）High-throughput sequencing of the microorganisms in the three reactors showed that the number of microorganisms in the three groups of samples was abundant.From the comprehensive analysis of Alpha diversity,rarefaction curve and Rank Abundance curve,it can be seen that the addition of Mn makes the distribution of microorganisms more uniform.The composition and relative abundance of microorganisms in the three groups of reactors were different,but Proteobacteria,Bacteroidetes,Firmicutes were the dominant phyla,and in the Mn system.Theε-Proteobacteria belonging to Proteobacteria all appeared;at the class level,Gammaproteobacteria,Bacterodia and Campylobacteria were all identified in the three reactors.The dominant bacteria class;cluster analysis at the genus level showed that the dominant bacteria genera in the three reactors were Sphaerotilus,Aeromonas and Arcobacter,different dominant bacteria genus and relative abundances caused differences in their denitrification abilities.（4）The results of the KEGG metabolic pathway showed that the microbes in the biofilter had a strong new city metabolism.And in the Mn-containing system,the microbial activity is higher,the denitrification ability is strong,and the expression of genes related to human diseases can be inhibited to a certain extent.By analyzing the metabolism of KO,it can be seen that the nitrogen cycle mainly includes four reduction pathways and two oxidation pathways.The four reduction pathways include nitrogen fixation,assimilated nitrate reduction,dissimilatory nitrate reduction and denitrification.The two oxidation pathways are nitrification and anaerobic ammonia oxidation.Among the carbohydrate metabolism pathways,glycolysis and pyruvate metabolism are the central pathways for the production of important precursor metabolites.These pathways are completed under the joint action of a variety of enzymes.