Enhanced biological nutrient removal by the alliance of a heterotrophic nitrifying strain with a nitrogen removing ecosystem

Nitrogen removal from synthetic wastewater was investigated in an airlift bioreactor （ALB）, augmented with a novel heterotrophic nitrifier Pseudonocardia ammonioxydans H9^T under organic carbon to nitrogen ratios （Corg/N） ranging from 0 to 12. Effect of the inoculated strain was also determined on the settling properties and the removal of chemical oxygen demand （COD）. Two laboratory scale reactors were set up to achieve a stable nitrifying state under the same physicochemical conditions of hydraulic retention time （HRT）, temperature, pH and dissolved oxygen （DO）, and operated under the sequencing batch mode. The level of DO was kept at 0.5- 1.5 mg/L by periodic stirring and aeration. Each specific Corg/N ratio was continued for duration of 3 weeks. One of the reactors （BR2） was inoculated with P ammonioxydans H9^T periodically at the start of each Corg/N ratio. Sludge volumetric index （SVI） improved with the increasing Corg/N ratio, but no significant difference was detected between the two reactors. BR2 showed higher levels of nitrogen removal with the increasing heterotrophic conditions, and the ammonia removal reached to the level of 82%-88%, up to10% higher than that in the control reactor （BR1） at Corg/N ratios higher than 6; however, the ammonia removal level in experimental reactor was up to 8% lower than that in control reactor at Corg/N ratios lower than 2. The COD removal efficiency progressively increased with the increasing Corg/N ratios in both of the reactors. The COD removal percentage up to peak values of 88%-94% in BR2, up to 11% higher than that in BR1 at Corg/N ratio higher than 4. The peak values of ammonia and COD removal almost coincided with the highest number （18%-27% to total bacterial number） of the exogenous bacterium in the BR2, detected as colony forming units （CFU）. Furthermore, the removal of ammonia and COD in BR2 was closely related to the number of the inoculated strain with a coefficient index （R2） up to 0.82 and 0.85 for ammonia and COD, respectively. These results suggest that it was more efficient for both the ammonia and carbon nutrient removals in a reactor inoculated with a heterotrophic nitrifier at high Corg/N ratio, inferring that the heterotrophic nitrifers would be practically more available in the treatment of wastewater with high level of ammonia and COD.

Purification and Characterization of a Low-temperature Hydroxylamine Oxidase from Heterotrophic Nitrifier Acinetobacter sp.Y16

Objective To purify a low-temperature hydroxylamine oxidase （HAO） from a heterotrophic nitrifying bacterium Acinetobacter sp. Y26 and investigate the enzyme property. Methods A HAO was purified by an anion-exchange and gel-filtration chromatography from strain Y16. The purity and molecular mass were determined by RP-HPLC and SDS-PAGE. The HAO activity was detected by monitoring the reduction of potassium ferricyanide using hydroxylamine as substrate and ferricyanide as electron acceptor. The partial amino acid sequence was determined by mass spectrometry. Results The low-temperature HAO with a molecular mass of 61 kDa was purified from strain Y26 by an anion-exchange and gel-filtration chromatography. The enzyme exhibited an ability to oxidize hydroxylamine in wide temperature range （4-40 ℃） in vitro using hydroxylamine as substrate and ferricyanide as electron acceptor. It was stable in the temperature range of 4 to 25 ℃ and pH range of 6.0 to 8.5 with less than 30% change in its activity. The optimal temperature and pH were 15 ℃ and 7.5, respectively. Three peptides were determined by mass spectrometry which were shown to be not identical to other reported HAOs. Conclusion This is the first study to purify a low-temperature HAO from a heterotrophic nitrifier Acinetobecter sp. It differs from other reported HAOs in molecular mass and enzyme properties. The findings of the present study have suggested that the strain Y26 passes through a hydroxylamine-oxidizing process catalyzed by a low-temperature HAO for ammonium removal.

Impact of 17β-Estradiol on Natural Water’s Heterotrophic Nitrifying Bacteria

In this research, bottom water samples were collected from nature water. After cultivating and selecting, bacteria which could use (NH4)2SO4 as the only nitrogen source had been selected. The bacteria were cultivated in BM cultures with 0, 0.1, 1, 10, 100 ng/L 17β-estradiol (E2), and the initial concentration of E2 is the only difference between cultures of each group. BM culture is a kind of bacteria culture with 100 mg/L of NH4-N as only nitrogen source. Every group’s N- NH4+, N- NO3-concentration and OD600 were measured. The result shows that compared with the control group, in which no E2 was added, the growth of heterotrophic nitrifying bacteria had been promoted when the concentration of E2 was in range of 1 - 100 ng/L. In addition, heterotrophic nitrifying bacteria’s growing speed has a positive correlation between the E2’s concentration. However, low concentration of E2 (like 0.1 ng/L), could inhibit the growth of heterotrophic nitrifying bacteria. Considering the impact of E2 on heterotrophic nitrifying bacteria, it is necessary to intensify the detection of E2 in the future.