Study On Nitrogen Removal Efficiency,Microbial Metabolism Characteristics Of Denitrifying Filter Using Endogenous Carbon Sources

Due to the high content of nitrogen and phosphorus,the artificial landscape water in most cities of the country is facing a serious problem of eutrophication and the loss of the landscape function of the water,which is in contradiction with the human needs for improving the living environment and improving the quality of life.The urban landscape water generally has the characteristics of low C/N.Therefore,the traditional water treatment process can’t effectively remove the pollutants.The treatment of low carbon and high nitrogen water developed slowly because of the restriction of carbon and nitrogen ratio and the cost of carbon source and the difficulty of operation.In this study,the endogenous carbon source denitrification reactor was used to reduce the carbon source in the process of nitrogen removal from low carbon and high nitrogen water.By switching the inlet direction of the reactor,a continuous "accumulation and utilization" process(use of endogenous carbon source)was realized at all levels of the reactor,so as to achieve the goal of denitrification by using endogenous carbon sources under low carbon conditions.This paper is based on a complete cycle of denitrifying biofilter,which has been operating steadily for two years,with a complete cycle of the reactor switching from inlet direction of F to R.The performance of pollutant removal,characteristics of microbial metabolism and succession of microbial community were studied during the three periods,concluding the stable operation period of inlet direction of F and R,and the initial stage of switching inlet direction(transition period).The main contents are as follows:(1)The removal of nitrate nitrogen,total nitrogen,nitrite nitrogen,CODCr,turbidity of the reactor in a complete commutation cycle was studied : during the inlet direction of F and the inlet direction of R,the removal of total nitrogen and nitrate nitrogen could reach more than 35% and 40%,the concentration of influent nitrite nitrogen fluctuates greatly but the effluent was less than 0.1mg/L,and the removal of influent nitrite was over 80%,the removal of CODCr in these two periods was about 60%,the turbidity of the influent water also fluctuates greatly,but the effluent is basically below 1 NTU,and the removal of turbidity can reach more than 85%;when the inlet direction of the reactor switched from F to R,due to the impact of changing operating conditions on microbes and the erosion of water flow to the biofilm in the back of the reactor(forward water end),the removal of water quality decreased,and the CODCr and turbidity of effluent even appeared higher than that of influent water.The transitional reversal period kept about 20 days.Meanwhile,in the three periods of the reactor,the change of dissolved oxygen showed a gradual decrease trend.The dissolved oxygen concentration in the back of the reactor was lower than 0.5 mg/L;the biomass at the inlet of the reactor increased rapidly during the operation in both influent directions.The biomass in the back of the reactor showed a decreasing trend in the use of endogenous carbon sources.(2)The Biolog-ECO plates were used to analyze the metabolic characteristics of microbial communities at all levels during the three periods of the reactor.AWCD values of the last two levels were lower than the previous two with the change of incubation time.The AWCD values at all levels of the transitional period were lower than that at the stable period of inlet direction of F and R,while the relative metabolic activity of microbial activity was not high during the transitional period.The first two levels of the microbial diversity index distribution were lower than the last two levels and the transitional period was diversified.The diversity index of the latter two levels was higher than that of the previous both at the stable period of inlet direction of F and R.In the stable period of inlet direction of F and R,the utilization of carbohydrate in grade I accounted for the most,and the utilization of acid in grade III and IV were the highest.The proportion of utilization of carbon sources at all levels in the transitional period was not obvious.According to the trend of DQ-fd,the dominant substrate of grade I was carbohydrate,the dominant substrate of grade II,III and IV was acid.DQ and fd values of grade III are the highest,which indicate that the utilization potential of acidic substances and related microbial abundance are the highest;By principal component analysis,three principal components were extracted from 31 carbon sources on the Biolog-ECO board at all levels of the reactor.The level III was positively correlated with PC1,the correlation was the highest,the correlation was low with the PC3,the level I was negatively correlated with PC1 and the correlation was high,and the highest carbon source of PC1 species was acid,which has a significant effect on the spatial distribution of microbial community metabolism.(3)High throughput sequencing technology was used to analyze the function of the microbes at all levels of the reactor at F and R to the stable operation period and the effect of the denitrification in the endogenous carbon source.When phylum was used as a taxonomic unit,Proteobacteria and Bacteroidetes were regarded as the dominant bacteria and accounted for more than 70%.When genus was used as a taxonomic unit,the denitrifying bacteria in the back of the reactor were slightly higher than that in the front,hydrolytic fermentation bacteria and bacteria whose main carbon sources were acids accounted for a certain proportion in the back of the reactor.The bacteria in the back of the reactor,represented by Pseudomonas spp.,were easily degrading and releasing organic matter under anaerobic conditions,thus as a carbon source in the back of the reactor,and in synergism with denitrifying bacteria to complete denitrification process of the reactor by using endogenous carbon source.