Facilitating nitrification and biofilm formation of Vibrio sp. by N-acyl-homoserine lactones in high salinity environment

The N-acyl-homoserine lactones (AHLs)-mediated quorum-sensing (QS) system played a crucial role in regulating biological nitrogen removal and biofilm formation. However, the regulatory role of AHLs on nitrogen removal bacteria in high salinity environment has remained unclear. This study evaluated the roles and release patterns of AHLs in Vibrio sp. LV-Q1 under high salinity condition. Results showed that Vibrio sp. primarily secretes five AHLs, and the AHLs activity is strongly correlated with the bacterial density. Exogenous C10-HSL and 3OC10-HSL were found to significantly enhance ammonium removal, while making a minor contribution to the growth rate. Both the C10-HSL and 3OC10-HSL promoted the biofilm formation of Vibrio sp. with an enhancement of 1.64 and 1.78 times, respectively. The scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM) observations confirmed the biofilm-enhancing effect of AHLs. Further analysis revealed that AHLs significantly improved bacterial self-aggregation and motility, as well as the level of extracellular polymeric substances (EPS). These findings provide significant guidance on construction of nitrification system at high salinity.

Nitrogen removal by a novel heterotrophic nitrification and aerobic denitrification bacterium Acinetobacter calcoaceticus TY1 under low temperatures

A new bacterial strain, Acinetobacter calcoaceticus TY1, was identified in activated sludge. This strain efficiently metabolized nitrogen from ammonium at low temperatures, utilizing NH₄⁺-N, NO₃^--N, and NO₂^--N as nitrogen sources. Of these, NH₄⁺-N was superior in terms of both assimilation and heterotrophic nitrification at 8 °C. The nitrogen metabolism-associated genes amoA, nirK, and nosZ were identified in TY1. Optimal requirements for growth and nitrogen removal were pH 7, shaking speed of 90 rpm, a C/N ratio of 10, and sodium citrate for the carbon supply. The ability to denitrify at low temperature suggests TY1's potential for wastewater management.

The immobilized Alcaligenes faecalis strain WT14 for removing high strength nitrate and reducing nitrite accumulation

Microbial immobilization is considered as one of the effective denitrification techniques in the treatment of high load wastewater. In this study, the immobilized cells consisting of polyvinyl alcohol (PVA), sodium alginate (SA), and calcium chloride (CaCl₂) were inoculated with Alcaligenes faecalis strain WT14 to treat wastewater with high nitrate-nitrogen (NO3--N) concentrations. After 48 h of wastewater treatment, 26.2-89.4% of total nitrogen (TN) was removed by the immobilized Alcaligenes faecalis strain WT14. The response surface methodology revealed the highest TN removal efficiency by Alcaligenes faecalis strain WT14 occurred at the immobilized ratio of 9.3% of PVA, 2.2% of SA and 1.9% of CaCl₂. Under the optimal ratio of PVA, SA, and CaCl₂, the conditions for the maximum denitrification efficiency and TN removal were pH of 7, temperature of 40°C, and shaking speed of 60 rpm·min^-1. Compared to the free cells, the immobilization cells had no obvious negative effect on denitrification efficiency, additionally reduced the nitrite accumulation, and thus improved the TN removal. Furthermore, the immobilized cells still maintained 95.4% of NO3--N removal after the eighth cycle reuse. These results demonstrated the immobilized Alcaligenes faecalis strain WT14 can remove TN effectively and additionally reduce nitrite accumulation in treating high strength NO3--N wastewater.

Simultaneous nitrification and denitrification of hypersaline wastewater by a robust bacterium Halomonas salifodinae from a repeated-batch acclimation

Biotreatment of hypersaline wastewater requires robust strains with high resistance to activity inhibition and even bacterium death, which remains a worldwide challenge. Here Halomonas salifodinae, a simultaneous nitrification and denitrification (SND) bacterium, was isolated by performing repeated-batch acclimation, showing efficient nitrogen removal at 0-15% salinity and low activity inhibition prominently superior to that of other strains such as Pseudomonas sp. and Acinetobacter sp. Community analysis as well as comparison of microbial activity at different salinities revealed an increased relative abundance of halotolerant populations by stimulating their salt tolerance during the repeated-batch process. For single or mixed nitrogen sources at 15% salinity, the SND efficiencies of the isolated strain reached above 95%. The high activities were attributed to the key enzymes AMO and HAO for nitrification as well as NAP and NIR for denitrification. The findings provide a promising acclimation pathway to obtain robust bacteria for biotreatment of hypersaline wastewater.

Nitrogen removal characteristics of a novel heterotrophic nitrification and aerobic denitrification bacteria, Alcaligenes faecalis strain WT14

Alcaligenes faecalis strain WT14 is heterotrophic nitrification and aerobic denitrification bacterium, newly isolated from a constructed wetland, and its feasibility in nitrogen removal was investigated. The result showed sodium citrate was more readily utilized by WT14 as a carbon source. The response surface methodology model revealed the highest total nitrogen removal by WT14 occurred at 20.3 °C, 113.5 r·min^-1, C/N 10.8, and pH 8.4. Under adapted environmental conditions, up to 55.9 mg·L^-1·h^-1 of ammonium nitrogen (NH₄⁺-N) was removed by WT14, and its NH₄⁺-N tolerance ability reached 2000 mg·L^-1. In addition to the reported high NH₄⁺-resistance of Alcaligenes faecalis, WT14 multiplied fast and had strong nitrate or nitrite removal capacity when high strength nitrate or nitrite was provided as the single nitrogen source; which differed from other Alcaligenes faecalis species. These results show WT14 is a novel strain of Alcaligenes faecalis and its nitrogen removal pathway will be carried out in the further study.

The nitrogen removal characterization of a cold-adapted bacterium: Bacillus simplex H-b

The removal efficacy of biological nitrogen removal process is inhibited by low temperatures. Herein, a psychrotrophic bacterium strain, Bacillus simplex H-b, was isolated and identified with the potential to conduct heterotrophic nitrification and aerobic denitrification in the temperature range from 5 to 37 °C. At 10 °C, the removal efficiencies of initial nitrate-N (63 mg/L), nitrite-N (10 mg/L) and ammonium-N (60 mg/L) were 67.29%, 78.69% and 82.16%, with the maximum removal rate of 0.56, 0.18 and 0.74 mg/L/h, respectively. Additionally, both the accumulation level of ATP (adenosine triphosphate) and the formation of extracellular polymeric substances was found to increase with the decrease of temperature from 37 °C to 10 °C, indicating strain H-b might resist low temperature stress through its cellular extreme environment resistant mechanism and further suggesting the newly isolated strain could serve as a promising candidate for nitrogen contaminated wastewater treatment, especially under low-temperature condition.

Nitrogen removal characteristics and predicted conversion pathways of a heterotrophic nitrification-aerobic denitrification bacterium, Pseudomonas aeruginosa P-1

In this study, the heterotrophic nitrification-aerobic denitrification activity of Pseudomonas aeruginosa (P-1) strain was investigated, and the N transformation pathway was revealed. The highest removal rates of NH₄⁺, NO₃^-, and NO₂^- (9.29, 6.12, and 3.72 mg L^-1 h^-1, respectively) by this strain were higher than those by most reported bacteria and were achieved when the carbon source was glucose, C/N ratio was 15, pH was 8, temperature was 30 °C, and shaking speed was 200 rpm. The removal order and characteristics of three N sources were investigated in Pseudomonas aeruginosa for the first time. The results revealed that P-1 preferentially nitrified NH₄⁺ and only began to denitrify NO₂^- and NO₃^- when NH₄⁺ was almost entirely depleted. Isotopic labeling of N sources revealed that P-1 uses both partial and complete nitrification/denitrification pathways that can operate either simultaneously or independently, depending on the availability of different types of N compounds, with N₂ as the final gaseous product and virtually no NO₂^- accumulation. Moreover, the P-1 strain could convert various nitrogen compounds under high salinity (40 g L^-1) and high concentrations of Cu²⁺, Zn²⁺, Cr⁶⁺, Pb²⁺, and Cd²⁺ (50 mg L^-1). Therefore, P-1 could be used as an alternative of inorganic N-removal bacteria in practical applications.

Simultaneous removal characteristics of ammonium and phenol by Alcaligenes faecalis strain WY-01 with the addition of acetate

In this study, simultaneous removal of ammonium plus phenol could be achieved by Alcaligenes faecalis strain WY-01 with the addition of acetate, although acetate delayed the phenol degradation, probably due to the delayed expression of phenol hydroxylase gene under the presence of acetate. Moreover, the successful expression of key enzyme genes in strain WY-01 provided some evidence to illustrate its metabolic pathways of ammonium and phenol under aerobic conditions. Furthermore, SEM was used to clarify the role of acetate in resisting phenol toxicity, and these results demonstrated that strain WY-01 has the ability to form cell flocs when sodium acetate is used as co-substrate for a high concentration of phenol, and these flocs could protect cells against the toxicity of phenol, further enhancing phenol degradation in a high concentration of phenol. All these will provide further insights into the efficacy of strain WY-01 for treating wastewater cocontaminated by ammonium and phenol.

Simultaneous reduction of nitrate and Cr(VI) by Pseudomonas aeruginosa strain G12 in wastewater

The interference of toxic heavy metals in the process of microbial aerobic denitrification is a hot issue in industry wastewater treatment in recent years. In this study, a multifunctional aerobic denitrifying bacterium - Pseudomonas aeruginosa G12 isolated from sewage sludge was used to explore the simultaneous removal ability to NO₃^--N and Cr(VI) in wastewater by a series of batch experiments. The results showed that G12 could effectively remove NO₃^--N (500 mg L^-1) and Cr(VI) (10 mg L^-1) by 98% and 93%, respectively. Meanwhile, the study found that the strain G12 had the potential to adapt to the complex external environment, including different carbon resources, nitrogen sources, and the coexisting heavy metals (Mn²⁺ and Cu²⁺). The strain G12 also had the considerable tolerance to initial NO₃^--N (100-700 mg L^-1) and Cr(VI) (1-20 mg L^-1) concentrations. The instrument analysis methods-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), from the molecular level, further confirmed that the strain G12 could remove NO₃^--N by aerobic denitrification, and the reduced functional groups (amino group, amide group, hydroxyl group and carboxyl group) on the surface of bacteria could transform Cr(VI) to Cr(III) (mainly CrCl₃). This study will offer a promising new microbial resource for nitrogen and Cr(VI) removal in industry wastewater treatment.

An innovative strategy for inducing Anammox from partial nitrification process in a membrane bioreactor

Anaerobic ammonium oxidation (Anammox) was an innovative process for nitrogen removal. In this study, CuO nanoparticles (NPs) was step-wise increasingly added to an MBR-based partial nitrification system, to investigate its feasibility for inducing Anammox and establishing autotrophic nitrogen removal system. Results showed that when CuO NPs was elevated to 5 mg L^-1, Anammox was successfully induced. The relative abundance of Nitrosomonas reached 13.73% while Candidatus Kuenenia increased to 4.79% from 0.46%, these two bacteria cooperatively contributed to the autotrophic nitrogen removal and improved the nitrogen removal rate (NRR) to 0.56 kg m^-3 d^-1 in 20 mg L^-1 NPs. However, 50 mg L^-1 NPs deeply suppressed the functional bacteria and decreased NRR to 0.14 kg m^-3 d^-1. Finally, the NPs removal, transformation and adsorption in the system were evaluated. It was concluded that CuO NPs in low concentration (5 mg L^-1) was effective for inducing Anammox and contributed to the survival of Anammox bacteria. The mechanism for inducing Anammox was attributed to the aggregation of CuO NPs which enabled the attached growth of AAOB as well as the suitable survival condition supplied by MBR.

Identification and Characterization of Janthinobacterium svalbardensis F19, a Novel Low-C/N-Tolerant Denitrifying Bacterium

Herein, we isolated Janthinobacterium svalbardensis F19 from sludge sediment. Strain F19 can simultaneously execute heterotrophic nitrification and aerobic denitrification under aerobic conditions. The organism exhibited efficient nitrogen removal at a C/N ratio of 2:1, with an average removal rate of 0.88 mg/L/h, without nitrite accumulation. At a C/N ratio of 2, an initial pH of 10.0, a culturing temperature of 25 °C, and sodium acetate as the carbon source, the removal efficiencies of ammonium, nitrate, nitrite, and hydroxylamine were 96.44%, 92.32%, 97.46%, and 96.69%, respectively. The maximum removal rates for domestic wastewater treatment for ammonia and total nitrogen were 98.22% and 92.49%, respectively. Gene-specific PCR amplification further confirmed the presence of napA, hao, and nirS genes, which may contribute to the heterotrophic nitrification and aerobic denitrification capacity of strain F19. These results indicate that this bacterium has potential for efficient nitrogen removal at low C/N ratios from domestic wastewater.

Ca(II) and Mg(II) significantly enhanced the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II)

This study investigated the impacts of alkaline-earth metals [Ca(II), Mg(II)] and heavy metals [Zn(II), Ni(II)] on the nitrogen removal capacity of Arthrobacter arilaitensis Y-10. StrainY-10 was able to tolerate 20 mg/L Ca(II) and its ammonium removal efficiency was 100%. 0.5 mg/L Ca(II) effectively promoted total nitrogen removal from wastewater containing nitrite. Mg(II) supplementation substantially enhanced the bacterial growth and nitrogen reduction. As Mg(II) concentrations increased from 0 to 2 mg/L, the ammonium, nitrate and nitrite removal efficiencies increased by 40.62%, 69.91% and 64.68%, respectively. Although the nitrogen removal ability of strain Y-10 was sharply hindered by Zn(II) and Ni(II), it occurred continuously even when the Zn(II) concentration reached 30 mg/L. However, the ammonium and total nitrogen removal almost stopped at 8 mg/L Ni(II), and the denitrification capacity was lost when the Ni(II) concentration exceeded 1 mg/L. The results demonstrate that Ca(II) and especially Mg(II) could significantly enhance the nitrogen removal capacity of Arthrobacter arilaitensis relative to Zn(II) and Ni(II).

Investigating the effect of copper and magnesium ions on nitrogen removal capacity of pure cultures by modified non-competitive inhibition model

Copper, a common heavy metal, may be beneficial for or poisonous to microbial activity. The objective of this study was to determine the effect of different copper ion concentrations on the nitrogen removal performance of Arthrobacter arilaitensis strain Y-10 and Pseudomonas taiwanensis strain J488. The non-competitive inhibition model was employed to evaluate the 50% inhibition concentrations (IC₅₀ values) of copper ions toward the pure strains. In the absence of magnesium ions, a low concentration of copper (0.1 mg/L) significantly enhanced the ammonium removal ability of strain Y-10 and its removal efficiency increased by 10.88% compared with the control treatment. Copper ranging from 0 to 0.1 mg/L had no significant effect on the ammonium removal capacity of strain J488. After adding 9.90 mg/L of magnesium to the basal medium, the effects of copper on nitrification of ammonium or denitrification of nitrate or nitrite were also assessed. In these conditions, 0.25 mg/L copper ions could strongly inhibit the ammonium, nitrate and nitrite removal activities for strain Y-10. For strain J488, no clear deterioration in ammonium removal efficiency was observed at copper ion concentrations below 0.5 mg/L, but 0.25 mg/L copper ions significantly inhibited nitrate and nitrite removal efficiencies, which were only 45.88% and 6.35%, respectively. The IC₅₀ values of copper ions for nitrate and nitrite removal by strain Y-10 were 0.195 and 0.090 mg/L respectively; for strain J488, the IC₅₀ values were 0.175 and 0.196 mg/L. The magnesium ions could improve the cell growth, nitrogen removal efficiency and copper ion resistance of bacteria.

Aerobic denitrification by Paracoccus sp. YF1 in the presence of Cu(II)

This study of Cu(II)'s impact on aerobic denitrification of Paracoccus sp. YF1 revealed that the denitrification rate decreased markedly from 99.8%, 98.0%, 68.7% to 16.3% when the concentrations of Cu(II) rose from 0, 0.01 mM, 0.05 mM to 0.1 mM, respectively. This outcome was confirmed by the successful test of OD₆₀₀, total protein and enzyme activities. As the concentration of Cu(II) increased from 0 to 0.1 mM, the total protein contents declined over a period of 48 h, and the activities of nitrate reductase (NR) and nitrite reductase (NIR) decreased remarkably during the first 24 h in a NO₃^- sufficient state. Meanwhile, the reduction of NO₃^- and NO₂^- was positively correlated with the expression level of NR and NIR. The removal rate of nitrate in the control treatment and different concentration of Cu(II) treatment fitted approximately to the zero-order model. Scanning electron microscopy (SEM) confirmed that the cell surfaces of Paracoccus sp. YF1 were disrupted when exposed to 0.1 mM Cu(II). The adsorption of Cu(II) onto the cells' surface was confirmed by Energy dispersive spectrometer (EDS), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy analysis (XPS). The insights obtained here regarding the influence of Cu(II) on aerobic denitrification will be of great significance for the treatment of heavy metals and nitrite co-existing sewage.

Optimization, purification, and characterization of hydroxylamine oxidoreductase from Acinetobacter sp. Y1

Hydroxylamine oxidoreductase (HAO) is a key enzyme involved in ammonium removal pathway. To further study the enzyme, HAO was purified from heterotrophic nitrifier Acinetobacter sp. Y1 and its property was investigated. Results of single-factor experiments showed that the optimal carbon source, nitrogen source, and C/N ratio were trisodium citrate, ammonium sulfate, and 14, respectively, with incubation time of 16 H. DEAE Sefinose^TM FF anion-exchange chromatography was used to purify HAO, followed by Sefinose^TM CL-6B gel filtration chromatography. SDS-PAGE revealed that a 47 kDa enzyme was purified successfully, with a purification fold of 7.32 and a recovery rate of 19.40%. The optimized enzyme activity of purified HAO was tested at pH 8.0 and 30 °C. The results showed that the activity was increased by 43.78% and 25.64% in the presence of 1 mM Fe²⁺ and Fe³⁺ , respectively. HAO activity was increased with the increase of Na⁺ and K⁺ , Mn²⁺ , Zn²⁺ , Cu²⁺ , Ca²⁺ , Ba²⁺ inhibited the HAO activity at three concentrations. In addition, HAO activity was activated by ethylenediaminetetraacetic acid at 0.4 mM, and a negative effect arose as the dose increased. The purified enzyme from Y1 is different from other reported HAOs. Further study should be conducted to investigate the enzyme.

Ammonium removal characteristics of an acid-resistant bacterium Acinetobacter sp. JR1 from pharmaceutical wastewater capable of heterotrophic nitrification-aerobic denitrification

A new acid-resistant bacterium Acinetobacter sp. JR1 was isolated, and its feasibility in nitrogen removal was investigated under acidic condition. Results show that JR1 indicated excellent ammonium and nitrate removal abilities with no accumulation of intermediates, and the maximum ammonium and nitrate removal efficiencies were 98.5% and 91.1%, respectively. Further experiments demonstrated that JR1 preferred to use ammonium with ammonium and nitrate as the mixed N-sources. For JR1, ammonium was assimilated directly as nutrients into cells and also converted into N₂ through heterotrophic nitrification-aerobic denitrification. Under acidic condition, JR1 performed comparable nitrogen removal abilities to other strains under neutral or weak alkaline environment, and the efficient removal of ammonium occurred at pH 4.5-10, C/N 12-24, 20-40 °C, DO ≥4.72 mg/L, 0-1.5% of salinity, 10 mg/L Zn²⁺ or 20 mg/L Mn²⁺. All these make JR1 a promising candidate for treating acidic wastewater containing nitrogen.

Seasonal-related effects on ammonium removal in activated carbon filter biologically enhanced by heterotrophic nitrifying bacteria for drinking water treatment

To determine the potential effects of seasonal changes on water temperature and water quality upon removal of ammonium and organic carbon pollutants and to characterize the variations in microbial characteristics, a pilot-scale activated carbon filter biologically enhanced with heterotrophic nitrifying bacteria was investigated for 528 days. The results show that 69.2 ± 28.6% of ammonium and 23.1 ± 11.6% of the dissolved organic carbon were removed by the biologically enhanced activated carbon (BEAC) reactor. It is shown that higher biodegradable dissolved organic carbon enhances ammonium removal, even at low temperatures. The C/N ratio consumed by the BEAC reactor reached a steady value (i.e., 3.3) after 2 months of operation. Despite seasonal fluctuations and competition of the indigenous community, the heterotrophic nitrifying bacteria (Acinetobacter sp. HRBLi 16 and Acinetobacter harbinensis strain HITLi 7) remained relatively stable. The amount of carbon source was the most significant environmental parameter and dramatically affected the microbial community compositions in the BEAC reactor. The present study provides new insights into the application of a BEAC reactor for ammonium removal from drinking water, resisting strong seasonal changes.

Short-term and long-term effects of Zn (II) on the microbial activity and sludge property of partial nitrification process

Autotrophic nitrogen removal was an innovative and economical nitrogen removal technology with less oxygen and no organics consumption, in which partial nitrification (PN) is the key component. It is necessary to clear the impact of metal ions on PN since the development of industry increased their opportunity for entering into wastewater. In this study, PN process was successfully started-up in an SBR, the short-term and long-term effects of Zn (II) on microbial bioactivity and the sludge adsorption ability for Zn (II) were investigated. Results suggested that low Zn (II) were favorable for AOB bioactivity, while the long-term effect also induced NOB bioactivity. The suppression threshold of Zn (II) on AOB in short-term effect was 10mgL^-1, which rose to 50mgL^-1 in the long-term effect due to the self-adaption. The PN sludge presented prominent absorbability for zinc and performed a quadratic relation with the Zn (II) concentration.

An adsorption-release-biodegradation system for simultaneous biodegradation of phenol and ammonium in phenol-rich wastewater

The feasibility of simultaneous biodegradation of phenol and ammonium in phenol-rich wastewater was evaluated in a reusable system, which contained macroporous adsorption resin and Alcaligenes faecalis strain WY-01. In the system, up to 6000mg/L phenol could be completely degraded by WY-01; meanwhile, 99.03±3.95% of ammonium was removed from the initial concentration of 384mg/L. This is the first study to show the capability of single strain in simultaneous removal of ammonium and phenol in wastewater containing such high concentrations of phenol. Moreover, the resin was regenerated during the biodegradation process without any additional manipulations, indicating the system was reusable. Furthermore, enzyme assay, gene expression patterns, HPLC-MS and gas chromatography analysis confirmed that phenol biodegradation accompanied with aerobic nitrifier denitrification process. Results imply that the reusable system provides a novel strategy for more efficient biodegradation of phenol and ammonium contained in some particular industrial wastewater.