Community Structure Of Aerobic Denitrifiers In Water Source Reservoirs And Experiment Of Enhanced Denitrification Characteristics

At present,water source reservoirs have become the main surface drinking water source in most cities and towns,and play an important role in urban water supply.However,with the development of society,the pollution of reservoirs has intensified,resulting in eutrophication,algae blooms and causes a series of water pollution problems in summer,which seriously endanger the safety of drinking water.Nitrogen is one of the most critical factors leading to water quality problems.In this study,Based on the continuous monitoring of the conventional water quality of Lijiahe Reservoir for one year,the pollution status of the reservoir water was analyzed.Aiming at the prominent problem of nitrogen pollution in Lijiahe Reservoir,this study focused on finding an economical and feasible method about microbial nitrogen removal,mainly studied:1)Identification and classification of nirS-type denitrifying bacteria in Lijiahe Reservoir and the changes of water quality and nirS-type denitrifying bacteria structure in Lijiahe Reservoir during induced mixing period;2)Screening of Iron-reducing Denitrifying Bacteria and Its Nitrogen Removal Characteristics;3)Feasibility and sustainability of enhanced nitrogen removal from raw water by embedding iron reducing denitrifying bacteria combined with adding inorganic electron donor.The main results are as follows:（1）The vertical population diversity of nirS-type denitrifying bacteria tended to be consistent during the induced mixing period.At the level of Proteobactria,Proteobactria was the dominant phylum,and the relative abundance of each layer of water body reached more than 99%.In the vertical direction,the difference of nirS-type denitrification population structure in different water layers was small.Sulfuricaulis,Sulfuritalea and Candidatus Accumulibacter were the dominant genera in August-December 2021,and Pseudomonas,Gastrostyla and Unclassified were the dominant genera in February-March2022.The analysis of the symbiotic network of denitrifying bacteria showed that the community composition of nirS denitrifying bacteria in Lijiahe Reservoir was significantly different,which confirmed that the denitrifying bacteria in Lijiahe Reservoir ecosystem had complex interactions.Through RDA analysis,it can be seen that the population structure of nirS-type denitrifying bacteria in the three stages of Lijiahe Reservoir in August-September,October-December and February-March is highly similar,but different stages are affected by different environmental factors and their impact intensity is quite different.（2）The four groups of iron-reducing denitrifying bacteria screened from reservoir sediments were mainly distributed in Proteobacteria,with extremely high community diversity at the genus level.The two groups of oligotrophic iron-reducing denitrifying bacteria could reduce Fe³⁺to Fe²⁺,so as to use Fe²⁺as an electron donor for efficient denitrification.The total nitrogen removal rate of the two groups of oligotrophic iron-reducing denitrifying bacteria was more than 68%.The nitrate nitrogen removal rates of the two groups were more than 96%,and there was no accumulation of ammonia nitrogen and nitrite nitrogen during denitrification.Different environmental factors had significant effects on the denitrification characteristics of oligotrophic iron-reducing denitrifying bacteria.The inorganic electron donor is Fe²⁺and the denitrification ability is better in neutral and acidic environment.Low temperature and high C/N environment will inhibit the denitrification activity of the bacteria.With the increase of dissolved oxygen,nitrogen removal efficiency decreased,but also has facultative aerobic denitrification characteristics;the bacteria P10 has a good removal effect on nitrogen in the raw water with Fe³⁺,Fe²⁺and zero-valent iron powder,but the denitrification effect of iron powder is more lasting,which can provide Fe³⁺and Fe²⁺in the reaction system for a long time.（3）The total nitrogen removal rate of the first cycle reactor G was more than 78%,and the total nitrogen could be reduced to less than 1 mg/L,which met the quality standard requirements of class III surface water environment.At the same time,the aerobic denitrification period also has a good degradation effect on other pollutants（total phosphorus,organic matter）.The total phosphorus removal rate is more than 91%,and the permanganate index removal rate is more than 46%.The second and third cycles showed that reactor G had a good continuous effect on nitrogen removal,and also had a good degradation effect on other pollutants,indicating that under the addition of inorganic electron donor,the nitrogen removal effect of raw water by embedding and fixing iron-reducing denitrifying bacteria was feasible and continuous,which provided a new idea for strengthening biological aerobic nitrogen removal.The results of high-throughput sequencing showed that the abundance and diversity of the experimental group increased,and the addition of electron donor and target bacteria changed the water environment.The ratio of Actinomycetes increased significantly after the operation of reactor a（control group）,and the relative abundance of denitrification-related bacteria increased significantly after the operation of Reactor B-G（control group）,the abundances of main bacteria in reactor a decreased.The relative abundance of denitrifying bacteria in the reactor F and G was higher than that in other reactions,and the environment was more suitable for the growth and reproduction of nitrifying and denitrifying bacteria.