Abstract
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 < 0.05). High C/N was beneficial for nitrate reduction (p < 0.05). The nitrate removal efficiencies showed no significant differences among the tested inoculums dosage (p > 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.
Highlights
During the past few decades, more and more nitrogen has been discarded into the fresh water ecosystem, leading to serious environmental problems [1,2,3,4], such as eutrophication, algae bloom, and unsafe water [5,6], especially in drinking water reservoirs [7,8]
The low temperature resistant and oligotrophic denitrifying functional microorganism groups could be constructed by self-adjustment and eco-recombination and the results showed that the maximum removal rate of nitrate and total nitrogen (TN) could reach 46% and 53%, respectively, during operation under the conditions of temperature about 10 to 18 °C of the source water quality [39]
The isolated strain N299 with high nitrogen removal efficiency was obtained in this study, and was stored on SM slant medium at 4 °C and on SM Glycerin medium at −20 °C
Summary
During the past few decades, more and more nitrogen has been discarded into the fresh water ecosystem, leading to serious environmental problems [1,2,3,4], such as eutrophication, algae bloom, and unsafe water [5,6], especially in drinking water reservoirs [7,8]. Nitrogen removal in freshwater ecosystems is important. Physical (air stripping) [9] and chemical techniques (chemical precipitation) [10] are widely used to remove nitrogen from wastewater, as the traditional biological method (nitrification by autotrophs under aerobic conditions and denitrification by heterotrophs under anaerobic conditions) is impractical [11]. Conventional biological denitrification only occurs under anaerobic or anoxic conditions with the reduction from nitrate to nitrogen gas [12]. Oxygen inhibits the reaction steps, which makes them impractical in natural waters, especially reservoirs [13].
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