Study On The Performance Of Immobilized Denitrifying Bacteria In Constructed Wetland For Slightly-Polluted Water Treatment

As an ecological engineering technology,the constructed wetland has been widely used in the treatment of non-point water bodies,but the nitrogen removal efficiency in wetlands was affected by temperature,in addition,the accumulation of nitrite in denitrification could have toxic effects on denitrifying bacteria to hinder denitrification process.This paper was based on the current water quality situation of Erhai River(total nitrogen exceeded,ammonia does not exceeded,nitrate is relatively high),choosing nitrate as the target pollutant,using immobilized microbial technology to strengthen the nitrogen removal in wetlands.The efficient denitrifying bacteria was obtained by isolation and determination of denitrifying capability,and then it was identified species and phylogenetic position based on DNA sequence analysis.The denitrification performance of immobilized denitrifying bacteria under different conditions,such as pH,temperature,DO,and C/N,were investigated to study the denitrifying characteristics.The results showed that strain C was the most efficient denitrifying bacteria,and the removal rate of nitrate and total nitrogen were 98.83% and 98.36%,respectively,and the nitrite accumulation was only 0.28mg/L.The removal efficiency of nitrate was 8.59 mg N/(L·h)in 24 h.Phylogenetic analysis showed that strain C had 99.7% maximum sequence similarity with Pseudomonas stutzeri A1501.The biomass and density of immobilized particles was 15.67g/L and 0.93g/mL,respectively.In the experiment of denitrification performance treating slightly-polluted water,it was obvious to find that the influence of pH,temperature,DO on nitrogen removal of immobilized denitrifying bacteria were less than that of free ones.The optimized conditions for nitrogen removal of immobilized denitrifying bacteria were pH of 7,temperature of 30?,DO of 0.87~1.54 mg/L,and C/N of 5.In the study,the effects of different dosing positions on nitrogen removal in wetlands were compared,and the microbial community structure and function were analyzed using means of high-throughput sequencing.The results showed that the system dosing in upper layer got the best efficiency during the 50 days,and the removal rate of total nitrogen and nitrate were 60.31% and 64.98%,respectively.The results of microbial diversity index of each system showed that the microbial species diversity in the control system was higher than other systems,but overall,there were little differences between the four systems.The most abundant phylum was Proteobacteria in each system,and followed by Chloroflexi.Because of dosing immobilized denitrifying bacteria in systems,the subtle changes in microbial communities were occurred,such as the increased percentage of Nitrospira,conducive to improve the nitrogen removal.At last,the experiment was done to study the nitrogen removal in wetlands at low temperature.The results showed that the removal rate of total nitrogen and nitrate in the system dosing in upper layer were 50.86% and 55.06%,respectively,while that in the control system were 24.81% and 27.53% at 15?.This indicated that the resistant performance of immobilized denitrifying bacteria at low temperature still existed after dosing in wetlands,and it also exhibit better denitrification performance with the adaptation to the environment.