Influence of Temperature on Denitrification and Microbial Community Structure and Diversity: A Laboratory Study on Nitrate Removal from Groundwater

Temperature is an extremely important environmental condition in the application of microbial denitrification for nitrate removal from groundwater. Understanding the nitrate removal efficiency of groundwater and the diversity, composition, and structure of microbial communities under different temperature conditions is of great significance for effective mitigation of groundwater nitrate pollution. This study investigated the effects of temperature on denitrification at 15 degrees C, 25 degrees C, 40 degrees C, and 45 degrees C. Moreover, the characteristics of microbial community structure and diversity were analyzed by combining high-throughput sequencing and polymerase chain reaction methods in order to fully clarify the denitrification efficiency under different temperature conditions. According to laboratory batch experiments and the findings of previous research, glucose was set as the carbon source and changes in "three nitrogen" indicators of the four temperature systems were mainly tested to clarify the effectiveness of nitrate removal. The maximum removal rates of nitrate nitrogen at 15 degrees C, 25 degrees C, 40 degrees C, and 45 degrees C were 44.05%, 87.03%, 99.26%, and 92.79%, respectively. Therefore, the most efficient nitrate removal can be achieved at 40celcius. The Chao abundance indexes in the denitrification systems at 15 degrees C, 25 degrees C, 40 degrees C, and 45 degrees C were 1873, 352, 466, and 640, respectively. Therefore, the highest species richness was observed at 15 degrees C, but there were only a few dominant bacteria species. The composition of the bacterial community and the most dominant phylum varied at different temperatures. Among them, Gammaproteobacteria in Proteobacteria phylum plays an important role in the degradation of nitrate nitrogen. The relative abundance of Gammaproteobacteria at 15 degrees C, 25 degrees C, 40 degrees C, and 45 degrees C were 25.32%, 66.56%, 72.83%, and 3.47%. Tolumonas belongs to Gammaproteobacteria. The relative abundance of Tolumonas at 15 degrees C, 25 degrees C, 40 degrees C, and 45 degrees C were 9.41%, 65.47%, 62.49%, and 0.03%, respectively. The results of this study show that different temperature conditions affect the diversity, composition, and structure of the microbial community, thereby affecting the efficiency of denitrification for nitrate removal from groundwater.