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We studied the influences of water pressure and temperature on denitrification, and detected its nitrogen removal characteristics for providing evidence to remediate the micro-polluted reservoir source water.Mixed oligotrophic aerobic denitrification bacteria was obtained through enrichment, domestication, and screening processes, which was isolated from sediment in the source water reservoir; and the nitrogen removal characteristics was detected by an in-situ biological inoculation experiment (DO at 3–8 mg/L).Nitrate of the hard flask system (with water pressure influence) was removed completely, however, at 0.5, 5 m water layer, the nitrate removal rate of the soft flask reached 90.66%, 100%, other layers reached 99.61%, 80.55%, 67.01%, 64.73%. No nitrite accumulated. Because of bacteria death, ammonia had a slight increase. At the end of the experiment, in the 0.5, 5.0, 7.5, 10.0, 12.5 and 15.0 m water layer, the total nitrogen removal rates of hard flask reached 50.11%, 61.49%, 56.24%, 44.50%, 36.80% and 38.73%, however, that of soft system reached 33.47%, 60.61%, 43.98%, 36.28%, 27.52% and 28.57%. OD600 and pH first rose and then dropped. The mixed bacteria had prominent nitrogen removal ability between 11 °C and 30 °C.The mixed bacteria have a strong adaptability to temperature and the water pressure has a disadvantage to the nitrogen removal.

Denitrification is a major biological process that reduces nitrate to nitrogen gas (N2 or N2O). In shallow eutrophic reservoirs, this process can remove the largest portion of fixed nitrogen and play an important role in the self-purification of this ecosystem. To understand the structure of denitrifying communities in a shallow eutrophic reservoir, NirS-Type and NirK-Type denitrifier communities were explored using a MiSeq high-throughput sequencing technique. NirK and NirS are two functional marker genes for denitrification that encode copper- and cytochrome cd1-containing nitrite reductases, respectively, which catalyze the reduction of nitrite to nitric oxide. MiSeq sequencing revealed a total of 13 102 and 3490 OTUs with 97% similarity for NirS-Type and NirK-Type denitrifiers, which contained 4 and 5 phyla, and 22 and 21 genera for NirS-Type and NirK-Type denitrifiers, respectively. The ACE, Chao diversity, and Shannon richness estimates for NirS-Type denitrifiers were higher than those for NirK-Type denitrifiers. However, the Simpson richness exhibited the opposite trend. The denitrification community structure exhibited significantly seasonal variations during the whole experiment period based on the PCA, Hcluster analysis, OTUs distributions, community composition, and heat map analysis. Meanwhile, the RDA indicated that the total sediment nitrogen, aerobic denitrifiers, functional genes, denitrification rates, and temperature were critical environmental factors influencing the seasonal variation in the bacterial denitrification community.

Nitrogen is considered to be one of the most widespread pollutants leading to eutrophication of freshwater ecosystems, especially in drinking water reservoirs. In this study, an oligotrophic aerobic denitrifier was isolated from drinking water reservoir sediment. Nitrogen removal performance was explored. The strain was identified by 16S rRNA gene sequence analysis as Zoogloea sp. N299. This species exhibits a periplasmic nitrate reductase gene (napA). Its specific growth rate was 0.22 h−1. Obvious denitrification and perfect nitrogen removal performances occurred when cultured in nitrate and nitrite mediums, at rates of 75.53% ± 1.69% and 58.65% ± 0.61%, respectively. The ammonia removal rate reached 44.12% ± 1.61% in ammonia medium. Zoogloea sp. N299 was inoculated into sterilized and unsterilized reservoir source waters with a dissolved oxygen level of 5–9 mg/L, pH 8–9, and C/N 1.14:1. The total nitrogen removal rate reached 46.41% ± 3.17% (sterilized) and 44.88% ± 4.31% (unsterilized). The cell optical density suggested the strain could survive in oligotrophic drinking water reservoir water conditions and perform nitrogen removal. Sodium acetate was the most favorable carbon source for nitrogen removal by strain N299 (p &lt, 0.05). High C/N was beneficial for nitrate reduction (p &lt, 0.05). The nitrate removal efficiencies showed no significant differences among the tested inoculums dosage (p &gt, 0.05). Furthermore, strain N299 could efficiently remove nitrate at neutral and slightly alkaline and low temperature conditions. These results, therefore, demonstrate that Zoogloea sp. N299 has high removal characteristics, and can be used as a nitrogen removal microbial inoculum with simultaneous aerobic nitrification and denitrification in a micro-polluted reservoir water ecosystem.