Kinetic affinity index informs the divisions of nitrate flux in aerobic denitrification

Effects of Ion Combinations and Their Concentrations on Denitrification Performance and Gene Expressions of an Aerobic Strain Marinobacter Hydrocarbonoclasticus RAD-2

Salinity is one of the most important factors affecting the nitrogen-removal efficiency of denitrifying bacteria. A series of different ion combinations and salinity gradients were carried out to clarify the effects of ion types and concentrations on nitrogen removal by halophilic aerobic denitrifying bacteria RAD-2. Nitrate concentrations, nitrite concentrations, TAN concentrations, and OD600 were monitored to investigate their effects on denitrification in each group. The results showed that Na+, K+, and Cl- accelerated the denitrification process and improved nitrogen-removal efficiency at moderate additions, while Ca2+ and Mg2+ showed no significant effect. Na+ was effective alone, while K+ or Cl- needed to be combined with at least one of Na+, K+, or Cl- to achieve similar efficiency. The batch tests of salinity confirmed that the addition of a moderate concentration of NaCl/Na2SO4 could effectively improve nitrogen-removal efficiency, while excessive salinity might hinder denitrification metabolism. In the salinity range of 5~40‱, a 5‱ dosage might be the most economical method for strain RAD-2. Real-time PCR experiments on 17 key nitrogen metabolism-related genes revealed that chloride was widely involved in the nitrogen and carbon metabolism of microorganisms by altering cell osmotic pressure and opening ion channel proteins, thereby affecting the efficiency of denitrification. The results of this study may contribute to a better understanding of the different roles of various ions in aerobic denitrification and highlight the importance of salinity control in highly salted wastewater treatment.

High nitrous oxide (N2O) greenhouse gas reduction potential of Pseudomonas sp. YR02 under aerobic condition

Aerobic environments exist widely in wastewater treatment plants (WWTP) and are unfavorable for greenhouse gas nitrous oxide (N₂O) reduction. Here, a novel strain Pseudomonas sp. YR02, which can perform N₂O reduction under aerobic conditions, was isolated. The successful amplification of four denitrifying genes proved its complete denitrifying ability. The inorganic nitrogen (IN) removal efficiencies (NRE) were >98.0% and intracellular nitrogen and gaseous nitrogen account for 52.6-58.4% and 41.6-47.4% of input nitrogen, respectively. The priority of IN utilization was TAN > NO₃^--N > NO₂^--N. The optimal conditions for IN and N₂O removal were consistent, except for the C/N ratio, which is 15 and 5 for IN and N₂O removal, respectively. The biokinetic constants analysis indicated strain YR02 had high potential to treat high ammonia and dissolved N₂O wastewater. Strain YR02 bioaugmentation mitigated 98.7% of N₂O emission and improved 32% NRE in WWTP, proving its application potential for N₂O mitigation.

A mechanistic review on aerobic denitrification for nitrogen removal in water treatment

The traditional biological nitrogen removal technology consists of two steps: nitrification by autotrophs in aerobic circumstances and denitrification by heterotrophs in anaerobic situations; however, this technology requires a huge area and stringent environmental conditions. Researchers reached the conclusion that the denitrification process could also be carried out in aerobic circumstances with the discovery of aerobic denitrification. The aerobic denitrification process is carried out by aerobic denitrifying bacteria (ADB), most of which are heterotrophic bacteria that can metabolize various forms of nitrogen compounds under aerobic conditions and directly convert ammonia nitrogen to N₂ for discharge from the system. Despite the fact that there is no universal agreement on the mechanism of aerobic denitrification, this article reviewed four current explanations for the denitrification mechanism of ADB, including the microenvironment theory, theory of enzyme, electron transport bottlenecks theory, and omics study, and summarized the parameters affecting the denitrification efficiency of ADB in terms of carbon source, temperature, dissolved oxygen (DO), and pH. It also discussed the current status of the application of aerobic denitrification in practical processes. Following the review, the difficulties of present aerobic denitrification technology are outlined and future research options are highlighted. This review may help to improve the design of current wastewater treatment facilities by utilizing ADB for effective nitrogen removal and provide the engineers with relevant references.

Simultaneous removal of organic matter and nitrogen by heterotrophic nitrification-aerobic denitrification bacteria in an air-lift multi-stage circulating integrated bioreactor

This study aimed to propose a novel air-lift multi-stage circulating integrated bioreactor (AMCIB) to treat urban sewage. The AMCIB combined the reaction zone and sedimentation zone, the alternating circulation of activated sludge in separate aerobic and anaerobic environments facilitates the enrichment of HN-AD bacteria. The preliminary study showed that AMCIB had high removal efficiencies for COD, NH₄⁺-N, TN and TP under high dissolved oxygen (DO) concentration conditions, with average removal rates of 93.21 %, 96.04 %, 75.06 % and 94.30 %, respectively. IlluminaMiSeq sequencing results showed that the system successfully cultured heterotrophic nitrification-aerobic denitrification (HN-AD) functional bacteria (Pseudomonas, Acinetobacter, Aeromonas) that played a crucial role in sewage treatment, and Tetrasphaera was the central phosphorus removing bacteria in the system. Functional gene predictions showed that the HN-AD played a dominant role in the system.

Nitrogen cycling and microbial cooperation in the terrestrial subsurface

The nitrogen cycle plays a major role in aquatic nitrogen transformations, including in the terrestrial subsurface. However, the variety of transformations remains understudied. To determine how nitrogen cycling microorganisms respond to different aquifer chemistries, we sampled groundwater with varying nutrient and oxygen contents. Genes and transcripts involved in major nitrogen-cycling pathways were quantified from 55 and 26 sites, respectively, and metagenomes and metatranscriptomes were analyzed from a subset of oxic and dysoxic sites (0.3-1.1 mg/L bulk dissolved oxygen). Nitrogen-cycling mechanisms (e.g. ammonia oxidation, denitrification, dissimilatory nitrate reduction to ammonium) were prevalent and highly redundant, regardless of site-specific physicochemistry or nitrate availability, and present in 40% of reconstructed genomes, suggesting that nitrogen cycling is a core function of aquifer communities. Transcriptional activity for nitrification, denitrification, nitrite-dependent anaerobic methane oxidation and anaerobic ammonia oxidation (anammox) occurred simultaneously in oxic and dysoxic groundwater, indicating the availability of oxic-anoxic interfaces. Concurrent activity by these microorganisms indicates potential synergisms through metabolite exchange across these interfaces (e.g. nitrite and oxygen). Fragmented denitrification pathway encoding and transcription was widespread among groundwater bacteria, although a considerable proportion of associated transcriptional activity was driven by complete denitrifiers, especially under dysoxic conditions. Despite large differences in transcription, the capacity for the final steps of denitrification was largely invariant to aquifer conditions, and most genes and transcripts encoding N₂O reductases were the atypical Sec-dependant type, suggesting energy-efficiency prioritization. Results provide insights into the capacity for cooperative relationships in groundwater communities, and the richness and complexity of metabolic mechanisms leading to the loss of fixed nitrogen.

Synthetic organic antibiotics residues as emerging contaminants waste-to-resources processing for a circular economy in China: Challenges and perspective

Synthetic antibiotics have been known for years to combat bacterial antibiotics. But their overuse and resistance have become a concern recently. The antibiotics reach the environment, including soil from the manufacturing process and undigested excretion by cattle and humans. It leads to overburden and contamination of the environment. These organic antibiotics remain in the environment for a very long period. During this period, antibiotics come in contact with various flora and fauna. The ill manufacturing practices and inadequate wastewater treatment cause a severe problem to the water bodies. After pretreatment from pharmaceutical industries, the effluents are released to the water bodies such as rivers. Even after pretreatment, effluents contain a significant number of antibiotic residues, which affect the living organisms living in the water bodies. Ultimately, river contaminated water reaches the ocean, spreading the contamination to a vast environment. This review paper discusses the impact of synthetic organic contamination on the environment and its hazardous effect on health. In addition, it analyzes and suggests the biotechnological strategies to tackle organic antibiotic residue proliferation. Moreover, the degradation of organic antibiotic residues by biocatalyst and biochar is analyzed. The circular economy approach for waste-to-resource technology for organic antibiotic residue in China is analyzed for a sustainable solution. Overall, the significant challenges related to synthetic antibiotic residues and future aspects are analyzed in this review paper.

Characteristics of a novel heterotrophic nitrification and aerobic denitrification bacterium and its bioaugmentation performance in a membrane bioreactor

A novel bacteria with heterotrophic nitrification and aerobic denitrification ability was obtained from a membrane bioreactor (MBR) and identified as Acinetobacter sp. TSH1. The nitrogen removal characteristics, nitrogen balance analysis, kinetic characteristics, and enhanced biological treatment in MBR of the novel isolated strain TSH1 were determined. Results showed that strain TSH1 could remove approximately 96.6% of NH₄⁺-N, 82.9% of NO₂^--N and 98.7% of NO₃^--N in 24 h, and the corresponding maximum removal rates were 3.64 mg-N/(L·h), 1.77 mg-N/(L·h) and 3.94 mg-N/(L·h). The nitrogen balance analysis indicated that most of NH₄⁺-N (62.6%) and NO₃^--N (71.9%) were transformed to gaseous nitrogen. The kinetic experiments showed that strain TSH1 had a high K_m of 151.64 mg-NH₄⁺-N/L and 203.25 mg-NO₃^--N/L. The enhanced biological treatment of synthetic wastewater in MBR showed that the strain TSH1 can significantly improve the nitrogen removal efficiency.

Simultaneous nitrification and aerobic denitrification by a novel isolated Ochrobactrum anthropi HND19

The study aimed to isolate a novel strain with heterotrophic nitrification and aerobic denitrification ability and evaluate the nitrogen removal characteristics. Results showed that Ochrobactrum anthropi HND19 could remove approximately 98.6% of NH₄⁺-N (104.3 mg·L^-1) and 97.6% of NO₃^--N (98.6 mg·L^-1), and the removal rates achieved 4.28 and 4.01 mg-N/(L·h) by heterotrophic nitrification and aerobic denitrification. The optimal incubate conditions of strain HND19 were 120 rpm (shaking speed), 5 ‰ (salinity), 30 °C (temperature), 7.5 (C/N ratio) with sodium acetate as carbon resource. And the removal efficiency of the total nitrogen (TN) realized 73.4% under the optimal conditions. Functional genes (hao, napA, nirK, norB, and nosZ) involved in the nitrogen removal processes were successfully amplified from strain HND19. These findings indicate that the strain HND19 possesses great application feasibility in treating wastewater with high-intensity nitrogen.

Performance of Aerobic Denitrification by the Strain Pseudomonas balearica RAD-17 in the Presence of Antibiotics

Aerobic denitrification, one of the important nitrate metabolic pathways in biological denitrification, has been attracting increasing interest recently due to its functional advantages. In order to evaluate the effect of antibiotics on aerobic denitrification and guide practical engineering application of aerobic denitrification techniques, we evaluated the performance of aerobic denitrification by the strain Pseudomonas balearica RAD-17 in the presence of ciprofloxacin (CFX) and oxytetracycline (OTC). No significant negative impact on the performance of aerobic denitrification in the presence of CFX or OTC within the range of 50 to 300 μg L^-1 was found. Significant degradation of OTC was found within the range of 50 μg L^-1 to 300 μg L^-1 under aerobic denitrification conditions, while no degradation was found for CFX. Stimulation of cell growth occurred within the investigated range of antibiotics. Under anoxic or aerobic conditions, the addition of CFX or OTC changed the N₂O production trend. The results in the present study may play an important role in informing the use of aerobic denitrification techniques in the presence of antibiotics within environmentally relevant concentrations (<1 mg/L).

Characterization of a novel marine aerobic denitrifier Vibrio spp. AD2 for efficient nitrate reduction without nitrite accumulation

Aerobic denitrifiers have the potential to reduce nitrate in polluted water under aerobic conditions. A salt-tolerant aerobic denitrifier was newly isolated and identified as Vibrio spp. AD2 from a marine recirculating aquaculture system, in which denitrification performance was investigated via single-factor experiment, Box-Behnken experiment, and nitrogen balance analysis. Nitrate reductase genes were identified by polymerase chain reaction. Results showed that strain AD2 removed 98.9% of nitrate-nitrogen (NO₃^--N) with an initial concentration about 100 mg·L^-1 in 48 h without nitrite-nitrogen (NO₂^--N) accumulation. Nitrogen balance indicated that approximately 17.5% of the initial NO₃^--N was utilized for bacteria synthesis themselves, 4.02% was converted to organic nitrogen, 39.8% was converted to nitrous oxide (N₂O), and 31.1% was converted to nitrogen (N₂). Response surface methodology experiment showed that the maximum removal of total nitrogen (TN) occurred under the condition of C/N ratio 11.5, shaking speed 127.9 rpm, and temperature 30.8 °C. Sequence amplification indicated that the denitrification genes, napA and nirS, were present in strain AD2. These results indicated that the strain AD2 has potential applications for removing NO₃^--N from high-salinity (3%) wastewater.

Nitrogen removal by heterotrophic nitrifying and aerobic denitrifying bacterium Pseudomonas sp. DM02: Removal performance, mechanism and immobilized application for real aquaculture wastewater treatment

A bacterial strain was isolated and identified as Pseudomonas sp. DM02 from an aquaculture system. Strain DM02 showed efficient heterotrophic nitrification-aerobic denitrification capability. Total ammonia nitrogen (TAN, 10 mg/L) could be completely removed by strain DM02 within 12 h under low nutrient condition. Nitrogen mass balance indicated that 70.8% of the initial TAN was translated into gaseous nitrogen and 28.1% was converted into intracellular nitrogen. Various carbon sources can be used for nitrate removal (>95% within 28 h). The optimal conditions for TAN, nitrate and nitrite removal were pH 7 with carbon/nitrogen (C/N) ratios of 8, 12 and 12, respectively. The napA, nirK, and nosZ functional genes were successful amplified from strain DM02. Both bioaugmentation and immobilized technology of strain DM02 present ability (>88%) for continuous treatment of real aquaculture wastewater. This research indicated a great potential for practical application of Pseudomonas sp. DM02 in aquaculture wastewater treatment.

Interrelationships between tetracyclines and nitrogen cycling processes mediated by microorganisms: A review

Due to their broad-spectrum antibacterial activity and low cost, tetracyclines (TCs) are a class of antibiotics widely used for human and veterinary medical purposes and as a growth-promoting agent for aquaculture. Interrelationships between TCs and nitrogen cycling have attracted scientific attention due to the complicated processes mediated by microorganisms. TCs negatively impact the nitrogen cycling; however, simultaneous degradation of TCs during nitrogen cycling mediated by microorganisms can be achieved. This review encapsulates the background and distribution of TCs in the environment. Additionally, the main nitrogen cycling process mediated by microorganisms were retrospectively examined. Furthermore, effects of TCs on the nitrogen cycling processes, namely nitrification, denitrification, and anammox, have been summarized. Finally, the pathway and microbial mechanism of degradation of TCs accompanied by nitrogen cycling processes were reviewed, along with the scope for prospective studies.

Simultaneous aerobic denitrification and antibiotics degradation by strain Marinobacter hydrocarbonoclasticus RAD-2

Simultaneous denitrification and antibiotics (oxytetracycline, OTC and ciprofloxacin, CFX) degradation was evaluated using a typical aerobic denitrifying strain Marinobacter hydrocarbonoclasticus RAD-2. There was no significant influence on the aerobic nitrate removal efficiency of strain RAD-2 in the presence of these two antibiotics. Along with denitrification, the average degradation rate of 2.92 μg OTC L^-1h^-1 was achieved, while no degradation was observed for CFX. The growth behavior indicated that an insignificant inhibition effect could have occurred at an antibiotics dosage lower than 300 μg/L. The transcriptional results revealed that antibiotics exposure caused (<2h) down-regulation of the denitrifying related genes, but triggered a significant subsequent up-regulation (4 h). Less nitrous oxide productions were observed in both aerobic and anoxic denitrification processes with antibiotics. Overall, the hormesis effect caused by antibiotics exposure indicated a potential approach to enhance the co-metabolism degradation performance for nitrate and antibiotics in aerobic denitrification.