Abstract
Treatment of micro-polluted source water is receiving increasing attention because of environmental awareness on a global level. We isolated and identified aerobic denitrifying bacteria Zoogloea sp. N299, Acinetobacter sp. G107, and Acinetobacter sp. 81Y and used these to remediate samples of their native source water. We first domesticated the isolated strains in the source water, and the 48-h nitrate removal rates of strains N299, G107, and 81Y reached 33.69%, 28.28%, and 22.86%, respectively, with no nitrite accumulation. We then conducted a source-water remediation experiment and cultured the domesticated strains (each at a dry cell weight concentration of 0.4 ppm) together in a sample of source water at 20–26 °C and a dissolved oxygen concentration of 3–7 mg/L for 60 days. The nitrate concentration of the system decreased from 1.57 ± 0.02 to 0.42 ± 0.01 mg/L and that of a control system decreased from 1.63 ± 0.02 to 1.30 ± 0.01 mg/L, each with no nitrite accumulation. Total nitrogen of the bacterial system changed from 2.31 ± 0.12 to 1.09 ± 0.01 mg/L, while that of the control system changed from 2.51 ± 0.13 to 1.72 ± 0.06 mg/L. The densities of aerobic denitrification bacteria in the experimental and control systems ranged from 2.8 × 104 to 2 × 107 cfu/mL and from 7.75 × 103 to 5.5 × 105 cfu/mL, respectively. The permanganate index in the experimental and control systems decreased from 5.94 ± 0.12 to 3.10 ± 0.08 mg/L and from 6.02 ± 0.13 to 3.61 ± 0.11 mg/L, respectively, over the course of the experiment. Next, we supplemented samples of the experimental and control systems with additional bacteria or additional source water and cultivated the systems for another 35 days. The additional bacteria did little to improve the water quality. The additional source water provided supplemental carbon and brought the nitrate removal rate in the experimental system to 16.97%, while that in the control system reached only 3.01%, with no nitrite accumulation in either system. Our results show that aerobic denitrifying bacteria remain highly active after domestication and demonstrate the applicability of such organisms in the bioremediation of oligotrophic ecosystems.
Highlights
Economic and social development has resulted in massive amounts of nitrogenous compounds in environmental waters and led to the continuous deterioration of aquatic ecosystems [1,2,3,4,5] and eutrophication of some reservoirs [6,7], putting drinking water sources at great risk [5]
Our results show that aerobic denitrifying bacteria remain highly active after domestication and demonstrate the applicability of such organisms in the bioremediation of oligotrophic ecosystems
On the basis of the 16S rRNA gene sequences, strain N299 clustered with species from Zoogloea and strains G107 and 81Y clustered with species from Acinetobacter
Summary
Economic and social development has resulted in massive amounts of nitrogenous compounds in environmental waters and led to the continuous deterioration of aquatic ecosystems [1,2,3,4,5] and eutrophication of some reservoirs [6,7], putting drinking water sources at great risk [5]. Many physical [8], chemical [9], and biological methods [10] have been used to remove the nitrogenous compounds and purify polluted waters [11]. Bioremediation has attracted wide attention because it has lower maintenance costs and greater pollutant-removal performance than other methods [10], for example, remediation of uranium [12], toluene [13,14], and organic and metal contamination [15]. The reaction steps that use nitrate or nitrite as terminal electron acceptors are inhibited by oxygen [20]. There have been recent reports of aerobic denitrifying bacteria isolated from canals [22], soils [23], ponds [24], activated sludge [25], and lakes [26] that can simultaneously utilize oxygen and nitrate as electron acceptors
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