Effect of nitrate concentration, pH, and hydraulic retention time on autotrophic denitrification efficiency with Fe(II) and Mn(II) as electron donors.

The role of electron donors (Fe(2+) and Mn(2+)) in the autotrophic denitrification of contaminated groundwater by bacterial strain SY6 was characterized based on empirical laboratory-scale analysis. Strain SY6 can utilize Fe(2+) more efficiently than Mn(2+) as an electron donor. This study has shown that the highest nitrate removal ratio, observed with Fe(2+) as the electron donor, was approximately 88.89%. An immobilized biological filter reactor was tested by using three levels of influent nitrate (10, 30, and 50 mg/L), three pH levels (6, 7, and 8), and three levels of hydraulic retention time (HRT; 6, 8, and 12 h), respectively. An optimal nitrate removal ratio of about 95% was achieved at pH 6.0 using a nitrate concentration of 50 mg/L and HRT of 12 h with Fe(2+) as an electron donor. The study showed that 90% of Fe(2+) and 75.52% removal of Mn(2+) were achieved at pH 8.0 with a nitrate concentration of 50 mg/L and a HRT of 12 h. Removal ratio of Fe(2+) and Mn(2+) is higher with higher influent nitrate and HRT. A weakly alkaline environment assisted the removal of Fe(2+) and Mn(2+).

Characterization of the anaerobic denitrification bacterium Acinetobacter sp. SZ28 and its application for groundwater treatment.

Acinetobacter sp. SZ28 exhibited efficient autotrophic denitrification ability using Mn(2+) as an electron donor. Sequence amplification identified the presence of the nirS gene. Meteorological chromatography analysis showed that N2 was produced as an end product. Response surface methodology experiments showed that the maximum removal of nitrate occurred under the following conditions: Mn(2+) concentration of 143.56 mg/L, C/N ratio of 6.82, initial pH of 5.17, and temperature of 34.26 °C, where the initial Mn(2+) concentration produced the largest effect. In the groundwater experiment, nitrate levels decreased from 1.63 mg/L to 0 mg/L. Three-dimensional fluorescence analysis showed a decrease in the peak intensity of the original humus. Humus and the small-molecule amino acid tryptophan were detected. These results demonstrated that strain SZ28 is a suitable candidate for the simultaneous removal of nitrogen and Mn(2+) in groundwater treatment.

Heterotrophic nitrification and aerobic denitrification at low nutrient conditions by a newly isolated bacterium, Acinetobacter sp. SYF26.

A new strain, named SYF26, was isolated from the Hei He oligotrophic drinking-water reservoir in China. Based on its phenotypic and phylogenetic characteristics, the isolate was identified as a species of genus Acinetobacter. Strain SYF26 was able to grow at low NH4(+)-N concentrations (5.46 mg l(-1)), and the nitrification rate was 0.064 mg NH4(+)-N l(-1) h(-1). Low accumulation of nitrate and nitrite was observed throughout the ammonium removal experiment. Strain SYF26 reduced NO3(-)-N or NO2(-)-N. Nitrite reductase and periplasmic nitrate reductase were detectable. The putative nitrogen removal process carried out by the strain SYF26 is as follows: NH4(+)→NH2OH→NO2(-)→NO3(-), then NO3(-)→NO2(-)→N2. Response surface methodology analysis demonstrated that the maximum removal of ammonium occurred under the following conditions: NH4(+)-N concentration of 22.05 mg l(-1), C/N ratio of 4.31, initial pH of 7.78 and temperature of 29.73 °C, where initial pH and temperature had the largest influence on ammonium removal.