Ammonium removal by a novel oligotrophic Acinetobacter sp. Y16 capable of heterotrophic nitrification-aerobic denitrification at low temperature

Effect of carbon source on carbon and nitrogen metabolism of common heterotrophic nitrification-aerobic denitrification pathway

Pseudomonas sp. ZHL02, removing nitrogen via ammonia nitrogen (NH4+) → hydroxylamine (HN2OH) → nitrite (NO2-) → nitrate (NO3-) → NO2- → nitric oxide (NO) → nitrous oxide (N2O) pathway was employed for getting in-depth information on the heterotrophic nitrification-aerobic denitrification (HNAD) pathway from carbon oxidation, nitrogen conversion, electron transport process, enzyme activity, as well as gene expression while sodium succinate, sodium citrate, and sodium acetate were utilized as the carbon sources. The nitrogen balance analysis results demonstrated that ZHL02 mainly removed NH4+-N through assimilation. The carbon source metabolism resulted in the discrepancies in electron transport chain and nitrogen removal between different HNAD bacteria. Moreover, the prokaryotic strand-specific transcriptome method showed that, amo and hao were absent in ZHL02, and unknown genes may be involved in ZHL02 during the HNAD process. As a fascinating process for removing nitrogen, the HNAD process is still puzzling, and the relationship between carbon metabolism and nitrogen metabolism among different HNAD pathways should be studied further.

The response of structure and nitrogen removal function of the biofilm on submerged macrophytes to high ammonium in constructed wetlands

The ammonium exceedance discharge from sewage treatment plants has a great risk to the stable operation of subsequent constructed wetlands (CWs). The effects of high ammonium shocks on submerged macrophytes and epiphytic biofilms on the leaves of submerged macrophytes in CWs were rarely mentioned in previous studies. In this paper, the 16S rRNA sequencing method was used to investigate the variation of the microbial communities in biofilms on the leaves of Vallisneria natans plants while the growth characteristics of V. natans plants were measured at different initial ammonium concentrations. The results demonstrated that the total chlorophyll and soluble sugar synthesis of V. natans plants decreased by 51.45% and 57.16%, respectively, and malondialdehyde content increased threefold after 8 days if the initial NH4+-N concentration was more than 5 mg/L. Algal density, bacterial quantity, dissolved oxygen, and pH increased with high ammonium shocks. The average removal efficiencies of total nitrogen and NH4+-N reached 73.26% and 83.94%, respectively. The heat map and relative abundance analysis represented that the relative abundances of phyla Proteobacteria, Cyanobacteria, and Bacteroidetes increased. The numbers of autotrophic nitrifiers and heterotrophic nitrification aerobic denitrification (HNAD) bacteria expanded in biofilms. In particular, HNAD bacteria of Flavobacterium, Hydrogenophaga, Acidovorax, Acinetobacter, Pseudomonas, Aeromonas, and Azospira had higher abundances than autotrophic nitrifiers because there were organic matters secreted from declining leaves of V. natans plants. The analysis of the nitrogen metabolic pathway showed aerobic denitrification was the main nitrogen removal pathway. Thus, the nitrification and denitrification bacterial communities increased in epiphytic biofilms on submerged macrophytes in constructed wetlands while submerged macrophytes declined under ammonium shock loading.

Influence of increasing anode surface area on nitrite-absent ammonium oxidation in a continuous single-chamber bio-electrochemical system

Reducing energy consumption in conventional nitrogen removal processes is a crucial and urgent requirement. This study proposes an efficient electrode-dependent bio-electrochemical anaerobic ammonium (NH4+-N) oxidation (BE-ANAMMOX) process, employing a carbon brush as the electron acceptor and voltage of 0.8 V. The applied voltage facilitated the removal of NH4+-N with a maximum removal efficiency of 41% and a Coulombic efficiency of 40.92%, without the addition of nitrite (NO2--N). Furthermore, the NH4+-N removal efficiency demonstrated an increase corresponding to the increase in the anodic surface area. The bio-electrochemical NH4+-N removal achieved remarkable reductions, eliminating the need for O2 and NO2--N by 100%, lowering energy consumption by 67%, and reducing CO2 emissions by 66% when treating 1 kg of NH4+-N. An analysis of the microbial community revealed an increase in nitrifiers and denitrifiers, including Exiguobacterium aestuarii, Alishewanella aestuarii, Comamonas granuli, and Acinetobacter baumannii. This intricate process involved the direct conversion of NH4+-N to N2 by ANAMMOX bacteria through extracellular electron transfer, all without NO2--N. Thus, bio-electrochemical NH4+-N removal exhibits promising potential for effective nitrogen removal in wastewater treatment facilities.

Diversity, community structure, and abundance of nirS-type denitrifying bacteria on suspended particulate matter in coastal high-altitude aquaculture pond water

Denitrifying bacteria harboring the nitrate reductase S (nirS) gene convert active nitrogen into molecular nitrogen, and alleviate eutrophication in aquaculture water. Suspended particulate matter (SPM) is an important component of aquaculture water and a carrier for denitrification. SPM with different particle sizes were collected from a coastal high-altitude aquaculture pond in Maoming City, China. Diversity, community structure, abundance of nirS-type denitrifying bacteria on SPM and environmental influencing factors were studied using high-throughput sequencing, fluorescence quantitative PCR, and statistical analysis. Pseudomonas, Halomonas, and Wenzhouxiangella were the dominant genera of nirS-type denitrifying bacteria on SPM from the ponds. Network analysis revealed Pseudomonas and Halomonas as the key genera involved in the interaction of nirS-type denitrifying bacteria on SPM in the ponds. qPCR indicated a trend toward greater nirS gene abundance in progressively larger SPM. Dissolved oxygen, pH, temperature, and SPM particle size were the main environmental factors influencing changes in the nirS-type denitrifying bacterial community on SPM in coastal high-altitude aquaculture pond water. These findings increase our understanding of the microbiology of nitrogen cycle processes in aquaculture ecosystem, and will help optimize aquatic tailwater treatment strategies.

Electrospun nanofibers electrostatically adsorb heterotrophic nitrifying and aerobic denitrifying bacteria to degrade nitrogen in wastewater

Nanofibers were prepared by electrospinning a mixture of polycaprolactone and silica, and modified to improve the hydrophilicity and stability of the material and to degrade nitrogenous wastewater by adsorbing heterotrophic nitrifying aerobic denitrifying (Ochrobactrum anthropic). The immobilized bacteria showed highly efficient simultaneous nitrification-denitrification ability, which could convert nearly 90 % of the initial nitrogen into gaseous nitrogen under aerobic conditions, and the average TN removal rate reached 5.59 mg/L/h. The average ammonia oxidation rate of bacteria immobilized by modified nanofibers was 7.36 mg/L/h, compared with 6.3 mg/L/h for free bacteria and only 4.23 mg/L/h for unmodified nanofiber-immobilized bacteria. Kinetic studies showed that modified nanofiber-immobilized bacteria complied with first-order degradation kinetics, and the effects of extreme pH, temperature, and salinity on immobilized bacteria were significantly reduced, while the degradation rate of free bacteria produced larger fluctuations. In addition, the immobilized bacterial nanofibers were reused five times, and the degradation rate remained stable at more than 80 %. At the same time, the degradation rate can still reach 50 % after 6 months of storage at 4 °C. It also demonstrated good nitrogen removal in practical wastewater treatment.

Isolation and characterization of a cold-tolerant heterotrophic nitrification-aerobic denitrification bacterium and evaluation of its nitrogen-removal efficiency

With a view toward addressing the poor efficiency with which nitrogen is removed from wastewater below 10 °C, in this study, we isolated a novel cold-tolerant heterotrophic nitrification-aerobic denitrification (HN-AD) bacterium from a wetland and characterized its nitrogen removal performance and nitrogen metabolic pathway. On the basis of 16S rRNA gene sequencing, this strain was identified as a species of Janthinobacterium, designated J1-1. At 8 °C, strain J1-1 showed excellent removal efficiencies of 89.18% and 68.18% for single-source NH4+-N and NO3--N, respectively, and removal efficiencies of 96.23% and 79.64% for NH4+-N and NO3--N, respectively, when supplied with mixed-source nitrogen. Whole-genome sequence analysis and successful amplification of the amoA, napA, and nirK functional genes related to nitrogen metabolism provided further evidence in support of the HN-AD capacity of strain J1-1. The deduced HN-AD metabolic pathway of the strain was NH4+-N→NH2OH→NO2--N→NO3--N→NO2--N→NO→N2O. In addition, assessments of NH4+-N removal under different conditions revealed the following conditions to be optimal for efficient removal: a temperature of 20 °C, pH of 7, shaking speed of 150 rpm, sodium succinate as a carbon source, and a C/N mass ratio of 16. Given its efficient nitrogen removal capacity at 8 °C, the J1-1 strain characterized in this study has considerable application potential in the treatment of low-temperature wastewater.

Optimization of nitrogen removal conditions based on response surface methodology and nitrogen removal pathway of Paracoccus sp. QD-19

The strain Paracoccus sp. QD-19 was isolated from the sludge-water mixture of aerobic tanks at the southern wastewater treatment plant in Shenyang, China. The optimal nitrogen removal conditions for strain QD-19 were determined using the Plackett-Burman design, path of steepest ascent method, and response surface methodology (RSM). The optimum nitrogen removal conditions were C/N 12.93, temperature 37 °C, and shaking speed 175.50 r/min. Strain QD-19 achieved 83.82 ± 0.80 % nitrogen removal efficiency at 10 h under optimum conditions. Functional enzyme-encodinge genes amplified via 16S rRNA sequence analysis included amoA, hao, napA, nirS, nirK, norB, and nosZ. The results revealed that NH4+-N → NH2OH → NO2--N → NO3--N → NO2--N → NO → N2O → N2 was the pathway for heterotrophic nitrification - aerobic denitrification. The strain was used to treat wastewater from a sewage treatment plant under optimal response surface methodology conditions. As a result, the TN removal efficiency was 77.11 %. The findings demonstrated that strain QD-19 exhibits favorable potential for heterotrophic nitrification and aerobic denitrification (HN-AD) of actual wastewater, presenting a promising application for biological wastewater treatment.

Nitrogen removal by a strengthened comprehensive floating bed with embedded pellets made by a newly isolated Pseudomonas sp. Y1

A newly heterotrophic nitrification aerobic denitrification(HN-AD) bacterium Pseudomonas sp. Y1 with highly nitrogen removal ability was isolated from the activated sludge, TN removal rate of which was 99.73%. In this study, two types of different ecology floating bed systems were designed to achieve efficient nitrogen removal in the urban eutrophic landscape water body, one is the comprehensive ecological floating bed(CEFB) system with only Lythrum salicari and the other is the strengthened comprehensive ecological floating bed (SCEFB) system with both Lythrum and embedded pellets made by Y1. The TN removal rates of the CEFB system were 33.82%, 83.84% and 88.91% at 8±1℃, 15±1℃ and 25±1℃, respectively, while the TN removal rates of the SCEFB system increased by nearly 40%, 16% and 11% at the same environment, respectively. The result shows that the SCEFB system can purify the simulated water from surface water body class V to class IV. Thus it has a broad application prospect in the urban eutrophic landscape water body.

Removal of nitrate nitrogen by Pseudomonas JI-2 under strong alkaline conditions: Performance and mechanism

The nitrate nitrogen removal characteristics of Pseudomonas JI-2 under strong alkaline conditions and the composition and functional groups of extracellular polymeric substance were analyzed. Furthermore, nontargeted metabonomics and bioinformatics technology were used to investigate the alkaline tolerance mechanism. JI-2 removed 11.05 mg N/(L·h) of nitrate with the initial pH, carbon to nitrogen ratio and temperature were 11.0, 8 and 25 °C respectively. Even when the pH was maintained at 11.0, JI-2 could still effectively remove nitrate. JI-2 contains a large number of Na+/H+ antiporters, such as Mrp, Mnh (mnhACDEFG) and Pha (phaACDEFG), which can stabilize the intracellular acid-base environment, and SlpA can enable quick adaptation to alkaline conditions. Moreover, JI-2 responds to the strong alkaline environment by secreting more polysaccharides, acidic functional groups and compatible solutes and regulating key metabolic processes such as pantothenate and CoA biosynthesis and carbapenem biosynthesis. Therefore, JI-2 can survive in strong alkaline environments and remove nitrate efficiently.

Efficient heterotrophic nitrification by a novel bacterium Sneathiella aquimaris 216LB-ZA1-12T isolated from aquaculture seawater

High concentration of ammonia poses a common threat to the healthy breeding of marine aquaculture organisms. Since aquaculture water is rich in organic matter, heterotrophic nitrifying bacteria might play a crucial role in ammonia removal. However, their roles in ammonia oxidation remain unknown. Here, we report a novel strain isolated from shrimp aquaculture seawater, identified as Sneathiella aquimaris 216LB-ZA1-12T, capable of heterotrophic nitrification. It is the first characterized heterotrophic nitrifier of the order Sneathiellales in the class Alphaproteobacteria. It exhibits high activity in heterotrophic nitrification, removing nearly 94% of ammonium-N under carbon-constrained conditions in 8 days with no observed nitrite accumulation. The heterotrophic nitrification pathway, inferred based on detection and genomic data was as follows: NH4+→NH2OH→NO→NO2-→NO3-. While this pathway aligns with the classical nitrification pathway, while the significant difference lies in the absence of classical HAO and HOX encoding genes in the genome, which is common in heterotrophic nitrifying bacteria. In summary, this bacterium is not only valuable for studying the nitrifying mechanism, but also holds potential for practical applications in ammonia removal in marine aquaculture systems and saline wastewater.

Exploring influence mechanism of small-molecule carbon source on heterotrophic nitrification-aerobic denitrification process from carbon metabolism, nitrogen metabolism and electron transport process

The heterotrophic nitrification-aerobic denitrification (HNAD) process can remove nitrogen and organic carbon under aerobic conditions. To get the in-depth mechanism of the HAND process, a strain named Acinetobacter johnsonii ZHL01 was isolated, and enzyme activity, electron transport, energy production, and gene expression of the strain were studied with small-molecule carbon sources, including sodium citrate, sodium acetate, sodium fumarate, and sodium succinate. The HNAD pathway of ZHL01 was NH4+→NH2OH → NO, and nitrogen balance analysis shows that ZHL01 could assimilate and denitrify 58.29 ± 1.05 % and 16.58 ± 1.07 % of nitrogen, respectively. The assimilation, the nitrification/denitrification, and the respiration processes were regulated by the concentration of reduced nicotinamide adenine dinucleotide (NADH) produced from the different metabolic pathways of small-molecule carbon sources. The HNAD process occurs to reduce intracellular redox levels related to NADH concentrations. This discovery provides a theoretical basis for the practical application of HAND bacteria.

Sediment Bacteria in the Alpine Lake Sayram: Vertical Patterns in Community Composition

Bacterial communities inhabiting alpine lakes are essential to our understanding of ecosystem processes in a changing climate, but little has been reported about the vertical patterns of sediment bacterial communities in alpine lakes. To address this knowledge gap, we collected the 100 cm long sediment core from the center of Lake Sayram, the largest alpine lake in Xinjiang Uygur autonomous area, China, and used 16S rRNA gene-targeted amplicon sequencing to examine the bacterial populations. The results showed that bacterial diversity, as estimated by the Shannon index, was highest at the surface (6.9849 at 0-4 cm) and gradually decreased with depth up to 3.9983 at 68-72 cm, and then increased to 5.0927 at 96-100 cm. A total of 56 different phyla and 1204 distinct genera were observed in the sediment core of Lake Sayram. The bacterial community structure in the sediment samples from the various layers was dissimilar. The most abundant phyla in alpine Lake Sayram were Proteobacteria, Firmicutes, and Planctomycetes, accounting for 73%, 6%, and 4% of the total reads, respectively; the most abundant genera were Acinetobacter, Hydrogenophaga, and Pseudomonas, accounting for 18%, 12%, and 8% of the total reads, respectively. Furthermore, the relative abundance of Acinetobacter increased with sediment depth, while the relative abundance of Hydrogenophaga and Pseudomonas decreased with sediment depth. Our findings indicated that the nitrate-reducing bacteria (Acinetobacter, Hydrogenophaga, and Pseudomonas) may be prevalent in the sediment core of Lake Sayram. Canonical correspondence analysis showed that carbonate and total organic carbon (TOC) may be the main environmental factors affecting the vertical patterns of bacterial community composition (BCC) in the sediment of Lake Sayram. This work significantly contributes to our understanding of the BCC of sediments from alpine lakes in arid and semiarid regions.

Phylogenetic diversity, distribution, and gene structure of the pyruvic oxime dioxygenase involved in heterotrophic nitrification

Some heterotrophic microorganisms carry out nitrification to produce nitrite and nitrate from pyruvic oxime. Pyruvic oxime dioxygenase (POD) is an enzyme that catalyzes the degradation of pyruvic oxime to pyruvate and nitrite from the heterotrophic nitrifying bacterium Alcaligenes faecalis. Sequence similarity searches revealed the presence of genes encoding proteins homologous to A. faecalis POD in bacteria of the phyla Proteobacteria and Actinobacteria and in fungi of the phylum Ascomycota, and their gene products were confirmed to have POD activity in recombinant experiments. Phylogenetic analysis further classified these POD homologs into three groups. Group 1 POD is mainly found in heterotrophic nitrifying Betaproteobacteria and fungi, and is assumed to be involved in heterotrophic nitrification. It is not clear whether group 2 POD, found mainly in species of the Gammaproteobacteria and Actinobacteria, and group 3 POD, found simultaneously with group 1 POD, are involved in heterotrophic nitrification. The genes of bacterial group 1 POD comprised a single transcription unit with the genes related to the metabolism of aromatic compounds, and many of the genes group 2 POD consisted of a single transcription unit with the gene encoding the protein homologous to 4-hydroxy-tetrahydrodipicolinate synthase (DapA). LysR- or Cro/CI-type regulatory genes were present adjacent to or in the vicinity of these POD gene clusters. POD may be involved not only in nitrification, but also in certain metabolic processes whose functions are currently unknown, in coordination with members of gene clusters.

Low-carbon and high-ammonia nitrogen dispersed wastewater treatment: From "normal-sludge" to "low-sludge" to "no-sludge" modes

Several biological enhancements were implemented in the aerobic tank to address the challenges of treating expressway service sewage (ESS) with low-carbon and high-ammonia nitrogen using A/O-MBR technology, aiming to improve TN removal efficiency and reduce excessive sludge production. A novel moving bed biofilm reactor (MBBR) inoculated with heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was developed for ESS, and the results showed that HN-AD bacteria significantly improved TN removal efficiency, with an increase of 65% compared to the traditional activated sludge system. High-throughput sequencing revealed that Bacteroidotas contributed significantly to MBBR denitrification, and the genes nirK and nosZ played a significant role in denitrification. The HN-AD biofilm-forming MBBR achieved the transition of ESS treatment from "normal-sludge" mode to the more environmentally-friendly "low-sludge" and "no-sludge" modes by reducing the sludge concentration.

Pangenome-driven insights into nitrogen metabolic characteristics of Citrobacter portucalensis strain AAK_AS5 associated with wastewater nitrogen removal

Nitrogen metabolism in the genus Citrobacter is very poorly studied despite its several implications in wastewater treatment. In the current study, Citrobacter portucalensis strain AAK_AS5 was assessed for remediation of simulated wastewater supplemented with different inorganic nitrogen sources. Combination of (NH₄)₂SO₄ with KNO₃ was the most preferred for achieving high growth density followed by (NH₄)₂SO₄ and KNO₃ alone. This was in agreement with highest ammonical nitrogen removal of 92.9% in the presence of combined nitrogen sources and the corresponding nitrate nitrogen removal of 93% in the presence of KNO₃. Furthermore, these removal capacities were validated by investigating the uniqueness and the spread of metabolic features through pan-genomic approach that revealed the largest number of unique genes (2097) and accessory genes (705) in strain AAK_AS5. Of the total 44 different types of nitrogen metabolism-related genes, 39 genes were associated with the core genome, while 5 genes such as gltI, nasA, nasR, nrtA, and ntrC uniquely belonged to the accessory genome. Strain AAK_AS5 possessed three major nitrate removal pathways viz., assimilatory and dissimilatory nitrate reduction to ammonia (ANRA & DNRA), and denitrification; however, the absence of nitrification was compensated by ammonia assimilation catalyzed by gene products of the GDH and GS-GOGAT pathways. narGHIJ encoding the respiratory nitrate reductase was commonly identified in all the studied genomes, while genes such as nirK, norB, and nosZ were uniquely present in the strain AAK_AS5 only. A markedly different genetic content and metabolic diversity between the strains reflected their adaptive evolution in the environment thus highlighting the significance of C. portucalensis AAK_AS5 for potential application in nitrogen removal from wastewater.

Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective

With the extensive development of industrial livestock and poultry production, a considerable part of agricultural wastewater containing tremendous ammonium and antibiotics have been indiscriminately released into the aquatic systems, causing serious harms to ecosystem and human health. In this review, ammonium detection technologies, including spectroscopy and fluorescence methods, and sensors were systematically summarized. Antibiotics analysis methodologies were critically reviewed, including chromatographic methods coupled with mass spectrometry, electrochemical sensors, fluorescence sensors, and biosensors. Current progress in remediation methods for ammonium removal were discussed and analyzed, including chemical precipitation, breakpoint chlorination, air stripping, reverse osmosis, adsorption, advanced oxidation processes (AOPs), and biological methods. Antibiotics removal approaches were comprehensively reviewed, including physical, AOPs, and biological processes. Furthermore, the simultaneous removal strategies for ammonium and antibiotics were reviewed and discussed, including physical adsorption processes, AOPs, biological processes. Finally, research gaps and the future perspectives were discussed. Through conducting comprehensive review, future research priorities include: (1) to improve the stabilities and adaptabilities of detection and analysis techniques for ammonium and antibiotics, (2) to develop innovative, efficient, and low cost approaches for simultaneous removal of ammonium and antibiotics, and (3) to explore the underlying mechanisms that governs the simultaneous removal of ammonium and antibiotics. This review could facilitate the evolution of innovative and efficient technologies for ammonium and antibiotics treatment in agricultural wastewater.

Enhanced heterotrophic nitrification and aerobic denitrification performance of Glutamicibacter arilaitensis EM-H8 with different carbon sources

Different carbon sources for Glutamicibacter arilaitensis EM-H8 were evaluated for ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N) removal. Strain EM-H8 could rapidly remove NH₄⁺-N, NO₃^--N and NO₂^--N. The highest removal rates measured for different forms of nitrogen with different carbon sources were 5.94 mg/L/h for NH₄⁺-N with sodium citrate, 4.25 mg/L/h for NO₃^--N with sodium succinate, and 3.88 mg/L/h for NO₂^--N with sucrose. The Nitrogen balance showed that strain EM-H8 could convert 77.88% of the initial nitrogen into nitrogenous gas when NO₂^--N was selected as the sole nitrogen source. The presence of NH₄⁺-N increased the removal rate of NO₂^--N from 3.88 to 4.02 mg/L/h. In an enzyme assay, ammonia monooxygenase, nitrate reductase and nitrite oxidoreductase were detected at 0.209, 0.314, and 0.025 U/mg protein, respectively. These results demonstrate that strain EM-H8 performs well for nitrogen removal, and shows excellent potential for simple and efficient removal of NO₂^--N from wastewater.

Enhanced efficiency and mechanism of low-temperature biochar on simultaneous removal of nitrogen and phosphorus by combined heterotrophic nitrification-aerobic denitrification bacteria

In this study, three strains of heterotrophic nitrification-aerobic denitrification (HN-AD) capable of simultaneously removing phosphorus were isolated from activated sludge, and low-temperature coconut shell biochar was prepared. The metabolic effects of combined HN-AD bacteria on the total nitrogen (TN) and total phosphorus (TP) were investigated, and the enhanced efficiency and mechanism of low-temperature biochar on the combined bacteria were also explored. The results indicated that the combined bacteria could adapt to environmental impacts and multiple nitrogen sources. The low-temperature biochar containing more aliphatic carbon and oxygen-containing functional groups enhanced the metabolic activity of combined HN-AD bacteria and accelerated the electron transfer process during nitrogen and phosphorus degradation. The removal efficiencies of TN and TP increased by 68% and 88%, respectively, in the treatment of actual sewage by biochar attached with combined bacteria. The findings form a basis for the engineering utilization of HN-AD and are of great practical significance.

Biofilm stratification and autotrophic-heterotrophic interactions in a structured bed reactor (SBRIA) for carbon and nitrogen removal

The structured-bed reactor with intermittent aeration (SBRIA) is a promising technology for simultaneous carbon and nitrogen removal from wastewater. An in depth understanding of the microbiological in the reactor is crucial for its optimization. In this research, biofilm samples from the aerobic and anoxic zones of an SBRIA were analyzed through 16S rRNA sequencing to evaluate the bacterial community shift with variations in the airflow and aeration time. The control of the airflow and aeration time were essential to guarantee reactor performances to nitrogen removal close to 80%, as it interfered in nitrifying and denitrifying communities. The aeration time of 1.75 h led to establishment of different nitrogen removal pathways by syntrophic relationships between nitrifier, denitrifier and anammox species. Additionally, the predominance of these different species in the internal and external parts of the biofilm varied according to the airflow.

Disturbing ion regulation and excretion in medaka (Oryzias melastigma) gills by microplastics: Insights from the gut-gill axis

The accumulation of microplastics (MPs) in fish gills has been widely recognized, however, whether such stress could thereby impact the physiological responses of fish gills is still unknown. Here, we investigated the impacts of three sizes (400 nm, 4 μm, 20 μm) of polystyrene (PS) MPs on (Na⁺, K⁺, Cl^-) ions regulation and ammonia excretion in medaka Oryzias melastigma. Significantly increased net Na⁺ and K⁺ flux rates were observed transiently during 0-3 h and 3-9 h, but not during 9-24 h. Such results suggest that the physiological resilience of fish gills regarding Na⁺ and K⁺ regulation was unaffected upon the exposure to PS-MPs, probably evidenced by the increased secretion of mucus. However, Cl^- regulation and ammonia excretion were significantly impaired, partly in consistent with the damages of ionocytes. The adverse impacts of PS-MPs on Cl^- regulation and ammonia excretion were size-dependent, with significant disturbances observed in 4 μm and 20 μm treated group for Cl^- regulation, but only in 20 μm treated group for ammonia excretion. The specific enrichment of Shinella and lower abundance of function profiles related to ion transport and metabolism might be responsible for the specific disturbance of Cl^- regulation found in the 4 μm treated group. The enrichment of Gemmobacter also accounted for the disturbances of ammonia excretion in 20 μm treated group. Our results highlighted the impacts of PS-MPs on the physiological functions in fish gills.

Bioaugmentation performances with a powerful strain for nitrogen removal without N2O accumulation

N₂O is regarded as an inevitable intermediate during nitrogen removal, especially for wastewater treatment plants where good operating conditions would be required to mitigate N₂O releasing, which generally causes a high treatment cost. In this study, a novel bacterium capable of removing nitrogen without N₂O accumulation was isolated and identified as Citrobacter freundii XY-1. The nitrogen removal characteristics, nitrogen removal pathway, bioaugmentation in different reactors as well as microbial diversity were investigated. Results showed that 99.42% of NH+ 4-N and 95% of total organic carbon could be removed within 48 h with the corresponding removal rates being 4.03 mg/(L·h) and 39.42 mg/(L·h), respectively. It was inferred that traditional denitrification and N₂O generation do not exist in the pathway of removing nitrogen by XY-1 based on isotope analysis and functional genes detection. Bioaugmentations of XY-1 in both sequencing batch reactor and biological aerated filter significantly promoted the performances of nitrogen removal. The microbial diversity indicated that the relative abundance of strain XY-1 ranged from 45% to 66%, predominating throughout the running period. Overall, XY-1 could become an incredibly important candidate for the upgrading of wastewater treatment plants.

Integrative chemical and omics analysis of the ammonia nitrogen removal characteristics and mechanism of a novel oligotrophic heterotrophic nitrification-aerobic denitrification bacterium

A novel oligotrophic heterotrophic nitrification-aerobic denitrification bacterium designated as Pseudomonas sp. N31942, was isolated from a eutrophic lake. Strain N31942 exhibits high ammonia nitrogen removal ability in oligotrophic environment as ammonia nitrogen can be efficiently (86.97 %) removed within 10 h with no accumulation of nitrite. In the nitrification process, strain N31942 can convert ammonia into nitrate in the absence of hydroxylamine oxidase and nitrite oxidoreductase. As for the denitrification process, nitrate or nitrite were reduced to ammonia and further converted into glutamate by dissimilatory nitrate reduction pathway. Transcriptomic analysis detected 2080 differentially expressed genes. Among them, the expression of the related genes in dissimilatory nitrate reduction process was all up-regulated at low ammonia concentrations, which indicates that the strain has excellent nitrogen removal efficiency for further nitrogen removal. Integrative omics analyses revealed that strain N31942 may have two possible pathways for the NH₄⁺-N removal as direct GDH/GS-GOGAT pathway (NH₄⁺-N → Glutamate) and indirect GDH/GS-GOGAT pathway (NH₄⁺-N → NH₂OH → NO₂^--N → NO₃^--N → NO₂^--N → NH₄⁺-N → Glutamate). Moreover, strain N31942 also has excellent nitrogen removal ability for real sewage and 77.21 % total nitrogen could be removed within 48 h. The results presented here provide new insights into ammonia nitrogen removal characteristics and mechanism of heterotrophic nitrification-aerobic denitrification bacterium under oligotrophic conditions.

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.

Effect mechanism of individual and combined salinity on the nitrogen removal yield of heterotrophic nitrification-aerobic denitrification bacteria

One of the biggest challenges of applying heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria to treat high salt organic wastewater lies in the inhibitory effect exerted by salinity. To study the inhibition effect and underlying mechanism induced by different ion types and ion composition, the individual and combined effects of NaCl, KCl and Na₂SO₄ on HN-AD bacteria Acinetobacter sp. TAC-1 were systematically investigated by batch experiments. Results indicated that the ammonia nitrogen removal yield and TAC-1 activity decreased with increased salt concentration. NaCl, KCl and Na₂SO₄ exerted different degrees of inhibition on TAC-1, with half concentration inhibition constant values of 0.205, 0.238 and 0.110 M, respectively. A synergistic effect on TAC-1 was found with the combinations of NaCl + KCl, NaCl + Na₂SO₄ and NaCl + KCl + Na₂SO₄. The whole RNA resequencing suggested that transcripts of denitrification genes (nirB and nasA) were significantly downregulated with increased Na₂SO₄ concentration. Simultaneously, Na₂SO₄ stress disrupted cell respiration, DNA replication, transcription, translation, and induced oxidative stress. Finally, we proposed a conceptual model to summarize the inhibition mechanisms and possible response strategies of TAC-1 bacteria under Na₂SO₄ stress.

Characterization of heterotrophic nitrification by a thermotolerant Brevibacillus Agri N2 isolated from sewage sludge composting

A thermotolerant strain isolated from sewage sludge (SS) composting was identified as Brevibacillus Agri N2, which showed the efficient capability for heterotrophic nitrification under high-temperature conditions. Incubation at 60 °C, strain N2 could utilize 45.47% of ammonium nitrogen (99.64 mg/L), 68.89% of hydroxylamine nitrogen (51.14 mg/L) and 76.77% of nitrite nitrogen (55.20 mg/L), with a minor part of nitrogen loss for 1.64%, 2.82% and 5.01%, respectively. The successful detection of ammonia monooxygenase, hydroxylamine oxidase, and nitrate oxidoreductase and PCR amplification of amoA, hao and nxrA genes provided evidence of nitrification ability by strain N2. Furthermore, single-factor experiments indicated that the optimal conditions for efficient nitrification performance by strain N2 were succinate as carbon source, 50 °C, C/N 12, pH 8 and 200 r/min. Strain N2 could perform the complete nitrification process, with minimal nitrogen loss at high temperature conditions, which indicated it had the potential for practical application for reducing nitrogen loss of SS composting.

Performance of Paracoccus pantotrophus MA3 in heterotrophic nitrification-anaerobic denitrification using formic acid as a carbon source

Excess amount of nitrogen in wastewater has caused serious concerns, such as water eutrophication. Paracoccus pantotrophus MA3, a novel isolated strain of heterotrophic nitrification-anaerobic denitrification bacteria, was evaluated for nitrogen removal using formic acid as the sole carbon source. The results showed that the maximum ammonium removal efficiency was observed under the optimum conditions of 26.25 carbon to nitrogen ratio, 3.39% (v/v) inoculation amount, 34.64 °C temperature, and at 180 rpm shaking speed, respectively. In addition, quantitative real-time PCR technique analysis assured that the gene expression level of formate dehydrogenase, formate tetrahydrofolate ligase, 5,10-methylenetetrahydrofolate dehydrogenase, serine hydroxymethyltransferase, respiratory nitrate reductase beta subunit, L-glutamine synthetase, glutamate dehydrogenase, and glutamate synthase were up-regulated compared to the control group, and combined with nitrogen mass balance analysis to conclude that most of the ammonium was removed by assimilation. A small amount of nitrate and nearly no nitrite were accumulated during heterotrophic nitrification. MA3 exhibited significant denitrification potential under anaerobic conditions with a maximum nitrate removal rate of 4.39 mg/L/h, and the only gas produced was N₂. Additionally, 11.50 ± 0.06 mg/L/h of NH₄⁺-N removal rate from biogas slurry was achieved.

Enhanced denitrification of sewage via bio-microcapsules embedding heterotrophic nitrification-aerobic denitrification bacteria Acinetobacter pittii SY9 and corn cob

In this work, bio-microcapsules were prepared by embedding heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria (Acinetobacter Pittii SY9) and corn cob. Bio-microcapsules (20 g/L of corn cob and 30% v/v suspension of strain SY9) were porous (pore size 2579.74-3725.44 nm; porosity 53.6%-79.9%). Under the appropriate conditions (C/N > 2, temperature of 20-35 ℃, rotation speed of 100-120 rpm, pH of 7-9), TN removal efficiency of bio-microcapsules reached 94.4%, and 74.0% of nitrogen was converted into N₂. The results of kinetics fitting indicated that aerobic denitrification was the limiting step during HN-AD process. Bio-microcapsules could slow the carbon release of corn cob for 120 days, which ensuring high HN-AD performance even at low C/N of 2.8. Bio-microcapsule SBR could stably run for 88 days with TN removal efficiency > 90% for synthetic sewage. Bio-microcapsules embedding strain SY9 and corn cob have prospective applications for enhancing denitrification of sewage.

Isolation and Nitrogen Removal Efficiency of the Heterotrophic Nitrifying-Aerobic Denitrifying Strain K17 From a Rare Earth Element Leaching Site

K17, an indigenous and heterotrophic nitrifying-aerobic denitrifying bacterium, was isolated from the soil of a weathered crust elution-deposited rare earth ore leaching site in Longnan County, China. Strain K17 was identified as Pseudomonas mosselii. In this study, the morphological characteristics of strain K17 were observed and the optimal ammonia nitrogen removal conditions for the strain were studied using a single-factor experiment. Key enzyme activities were determined, and we also explored the ammonia nitrogen removal process of strain K17 on simulated leaching liquor of the rare earth element leaching site. Based on the determination of ammonia nitrogen removal and enzyme activity, it was found that strain K17 has both heterotrophic nitrifying and aerobic denitrifying activities. In addition, single-factor experiments revealed that the most appropriate carbon source for strain K17 was sodium citrate with a C/N ratio of 10 and an initial NH₄⁺-N concentration of 100 mg/l. Furthermore, the optimal initial pH and rotation speed were 7 and 165 r/min, respectively. Under optimal conditions, the ammonia nitrogen removal efficiency of strain K17 was greater than 95%. As an indigenous bacterium, strain K17 has great potential for treating residual ammonium leaching solutions from rare earth element leaching sites.

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.

Characterization of Alcaligenes aquatilis as a novel member of heterotrophic nitrifier-aerobic denitrifier and its performance in treating piggery wastewater

A novel strain AS1 with heterotrophic nitrifying-aerobic denitrifying capacity in the species of Alcaligenes aquatilis was isolated from the aerobic activated sludge. It showed a great capability of ammonia removal, and the aerobic metabolic pathways to yield gaseous-nitrogen by hydroxylamine oxidation and nitrite denitrification were proposed. AS1 could efficiently remove ammonia under a wide range of environmental conditions, including the ratio of chemical oxygen demand to total nitrogen: 15-30, pH: 6-10, NaCl: 0-60 g/L, shaking speed of 0-180 rpm, and succinate, acetate, or citrate as carbon source. In the treatment of actual piggery wastewater, 95.3%, 95.1% and 84.9% of NH₄⁺-N was removed by AS1 when the initial ammonia concentration was 500, 1300, and 2000 mg/L, respectively, with the maximum NH₄⁺-N removal rate of 30.5 mg/L/h and 569.7 mg/L/d. Furthermore, plate colony-counting showed that AS1 achieved an efficient proliferation. These results imply the application potential of AS1 in treating high-ammonia wastewater.

Simultaneous Nitrification and Denitrification under Aerobic Atmosphere by Newly Isolated Pseudomona aeruginosa LS82

Discharge of wastewater contained high amount of nitrogen would cause eutrophication to water bodies. Simultaneous nitrification and denitrification (SND) has been confirmed as an effective process, the isolation of SND bacteria is crucial for its successful operation. In this study, an SND strain was isolated and identified as Pseudomona aeruginosa LS82, which exhibited a rapid growth rate (0.385 h−1) and good nitrogen removal performance (4.96 mg N·L−1·h−1). Response surface methodology was applied to optimize the TN removal conditions, at which nearly complete nitrogen (99.8 ± 0.9%) removal were obtained within 18 h at the condition: pH 8.47, 100 rpm and the C/N ratio of 19.7. The saddle-shaped contours confirmed that the interaction of pH and inoculum size would influence the removal of total nitrogen significantly. Kinetic analyses indicated that the reduction of nitrite was the rate-limiting step in the SND process. Our research suggested strain LS82 can serve as a promising candidate for the treatment of ammonium rich wastewater, and expended our understanding the nitrogen removal mechanism in the SND process.

Wild Heterotrophic Nitrifying Strain Pseudomonas BT1 Isolated from Kitchen Waste Sludge Restores Ammonia Nitrogen Removal in a Sewage Treatment Plant Shocked by Thiourea

Thiourea is used in agriculture and industry as a metal scavenger, synthetic intermediate, and nitrification inhibitor. However, in wastewater, it can inhibit the nitrification process and induce the collapse of the nitrification system. In such a case, ammonia-oxidizing bacteria (AOB) lose their ability to remove ammonia. We investigated the nitrification system of a 60,000-t/d municipal sewage treatment plant in Nanjing, which collapsed after receiving 5–15 ppm (5–15 mg/L) thiourea. Ammonia nitrogen removal quickly recovered to more than 95% after inoculation with 10 t high-efficiency nitrification sludge, which was collected from a kitchen waste treatment plant. A heterotrophic nitrification strain was isolated from the inoculated sludge and identified as wild Pseudomonas by 16S rDNA sequencing and named “BT1.” Based on thiourea tolerance tests, BT1 can tolerate a thiourea content of more than 500 ppm. For comparison, the in situ process was imitated by the simulation system, and the wastewater shocked by 10 ppm thiourea could still meet the emission standard after adding 1% (V/V) BT1. High-throughput sequencing analysis was applied to study microbial succession during thiourea shock loading. The results showed that Hydrogenophaga and Thiobacillus grew with the growth of BT1. Pseudomonas BT1 was used for a 6,000-t/d printed circuit board (PCB) wastewater treatment system, the nitrification system returned to normal in 15 days, and the degradation rate stabilized at more than 95%.

Intrahabitat Differences in Bacterial Communities Associated with Corbicula fluminea in the Large Shallow Eutrophic Lake Taihu

The Asian clam Corbicula fluminea is a keystone zoobenthos in freshwater ecosystems. However, its associated microbiome is not well understood. We investigated the bacterial communities of this clam and its surrounding environment, including sediment and water simultaneously, in a large lake by means of 16S rRNA gene sequencing. Approximately two-thirds of the bacterial operational taxonomic units (OTUs) associated with clams were observed in the surrounding environment and mostly from particle-associated samples. The associated bacterial communities were site specific and more similar to environmental bacteria from the same site than those at other sites, suggesting a local environmental influence on host bacteria. However, the significant differences in bacterial diversities and compositions between the clam and the environment also indicated strong host selection pressure on bacteria from the surrounding environment. Bacteria affiliated with Firmicutes, Spirochaetes, Tenericutes, Bacteroidetes, Epsilonbacteraeota, Patescibacteria, and Fusobacteria were found to be significantly enriched in the clams in comparison to their local environment. Oligotyping analyses of the core-associated bacterial OTUs also demonstrated that most of the core OTUs had lower relative abundances and occurrence frequencies in environmental samples. The core bacterial OTUs were found to play an important role in maintaining the stability of the bacterial community network. These core bacteria included the two most abundant taxa Romboutsia and Paraclostridium with the potential function of fermenting polysaccharides for assisting host clams in food digestion. Overall, we demonstrate that clam-associated bacteria were spatially dynamic and site specific, which were mainly structured both by local environments and host selection. IMPORTANCE The Asian clam Corbicula fluminea is an important benthic clam in freshwater ecosystems due to its high population densities and high filtering efficiency for particulate organic matter. While the associated microbiota is believed to be vital for host living, our knowledge about the compositions, sources, and potential functions is still lacking. We found that C. fluminea offers a unique ecological niche for specific lake bacteria. We also observed high intrahabitat variation in the associated bacterial communities. Such variations were driven mainly by local environments, followed by host selection pressure. While the local microbes served as a source of the clam-associated bacteria, host selection resulted in enrichments of bacterial taxa with the potential for assisting the host in organic matter digestion. These results significantly advance our current understanding of the origins and ecological roles of the microbiota associated with a keynote clam in freshwater ecosystems.

Performance and nitrogen removal mechanism in a novel aerobic-microaerobic combined process treating manure-free piggery wastewater

A novel combined sequencing batch reactor (SBR) - up-flow microaerobic sludge reactor (UMSR) process was developed to treat manure-free piggery wastewater characterized by low COD/TN ratio and high NH₄⁺-N. The front-end SBR was designed to get an effluent with COD/TN ≤ 1 by removing COD, allowing the back-end UMSR to practice anammox for the simultaneous removal of TN and NH₄⁺-N. Fed with the raw piggery wastewater, the combined SBR-UMSR process was started up at 27℃ with a reflux ratio of 15:1 in the UMSR. After 230-days running, the removal of COD, TN, and NH₄⁺-N in the combined SBR-UMSR process reached 78.41%,85.05%, and 92.21%, respectively. 50.22% of COD in the wastewater was removed in the SBR, while 87.11% of NH₄⁺-N and 79.69% of TN were removed in the UMSR. Stoichiometry and bacterial function analysis revealed that the partial nitrification - anammox process was the dominant nitrogen removal approach in the UMSR.

Nitrogen Removal Characteristics and Constraints of an Alphaproteobacteria with Potential for High Nitrogen Content Heterotrophic Nitrification-Aerobic Denitrification

The discovery of heterotrophic nitrification-aerobic denitrification (HN-AD) microorganisms has opened a new window for wastewater treatment. The underlying mechanism of HN-AD, however, is not fully understood because of the phylogenetic diversity of HN-AD microbes. The isolation and characterization of new HN-AD microorganisms are encouraging for furthering the understanding of this process. In this study, we found an Alphaproteobacteria isolate W30 from a historically polluted river in China through an HN-AD microbes screening process, which we identified as Pannonibacter sp. A potential HN-AD pathway for W30 was proposed based on N conversion analyses and the successful amplification of the entire denitrification gene series. The isolate exhibited high efficiency of aerobic inorganic nitrogen transformation, which accounted for 97.11% of NH₄⁺-N, 100% of NO₃⁻-N, and 99.98% of NO₂⁻-N removal with a maximum linear rate of 10.21 mg/L/h, 10.46 mg/L/h, and 10.77 mg/L/h, respectively. Assimilation rather than denitrification was the main mechanism for the environmental nitrogen depletion mediated by W30. The effect of environmental constraints on aerobic NO₃⁻-N removal were characterized, following a membrane bioreactor effluent test under an oxic condition. Compared to known Alphaproteobacterial HN-AD microbes, we showed that Pannonibacter sp. W30 could deplete nitrogen with no NO₂⁻-N or NO₃⁻-N accumulation in the HN-AD process. Therefore, the application of Pannonibacter sp. W30 has the potential for developing a felicitous HN-AD technology to treat N-laden wastewater at the full-scale level.

Heterotrophic nitrification and aerobic denitrification process: Promising but a long way to go in the wastewater treatment

The traditional biological nitrogen removal (BNR) follows the conventional scheme of sequential nitrification and denitrification. In recent years, novel processes such as anaerobic ammonia oxidation (anammox), complete oxidation of ammonia to nitrate in one organism (comammox), heterotrophic nitrification and aerobic denitrification (HN-AD), and dissimilatory nitrate reduction to ammonium (DNRA) are gaining tremendous attention after the discovery of metabolically versatile bacteria. Among them, HN-AD offers several advantages because individual bacteria could achieve one-stage nitrogen removal under aerobic conditions in the presence of organic carbon. In this review, besides classical BNR processes, we summarized the existing literature on HN-AD bacteria which have been isolated from diverse habitats. A particular focus was given on the diversity and physiology of HN-AD bacteria, influences of physiological and biochemical factors on their growth, nitrogen removal performances, as well as limitations and strategies in unraveling HN-AD metabolic pathways. We also presented case studies of HN-AD application in wastewater treatment facilities, pointed out forthcoming challenges of HN-AD in these systems, and presented modulation strategies for HN-AD application in engineering. This review may help improve the existing design of wastewater treatment plants by harnessing HN-AD bacteria for effective nitrogen removal.

Influence mechanism of C/N ratio on heterotrophic nitrification- aerobic denitrification process

A heterotrophic nitrification- aerobic denitrification (HNAD) bacterium, Acinetobacter junii ZHG-1, was isolated, meanwhile, the optimal conditions for the strain were evaluated, moreover, the influence mechanism of the C/N ratio on the HNAD process was investigated from the perspective of electron transport and energy level. The increasing of C/N ratio enhanced the reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD⁺) ratio, NADH concentration, electron transport system activity (ETSA), ATP content, as well as enzymes activities, consequently, the HNAD performance of the strain can be improved, however, when the C/N ratio was higher than 30, the activities of enzymes relating to the HNAD process and the ETSA had reached the maximum, which might limit the further improvement of the nitrogen removal with the increasing of C/N ratio. As the interaction between different biochemical reactions in HNAD process, more efforts should be devoted to the influent mechanism of different environmental factors on the HNAD process.

A review of research progress of heterotrophic nitrification and aerobic denitrification microorganisms (HNADMs)

Traditional nitrogen removal relies on the autotrophic nitrification and anaerobic denitrification process. In the system, autotrophic microorganisms achieve nitrification under aerobic condition and heterotrophic microorganisms complete the denitrification in anaerobic condition. As the two types of microorganisms have different tolerance on oxygen concentration, nitrification and denitrification are normally set in two compartments for high nitrogen removal. Therefore, large land occupying is required. In fact, there is a special type of microorganism called heterotrophic nitrification & aerobic denitrification microorganisms (HNADMs) which can oxidize ammonium nitrogen, and perform denitrification in the presence of oxygen. HNADMs have been reported in many environments. It was found that HNADMs could simultaneously achieve nitrification and denitrification. In addition, some HNADMs not only have the ability to remove nitrogen, but also have the ability to remove phosphorus. It suggests that HNADMs have great potential for pollution removal from wastewater. So far, individual work on single strain was carried out. Comprehensive summary of the HNADMs would provide a better picture for understanding and directing its application. In this paper, the studies related on HNADMs were reviewed. The nitrogen metabolism pathway of HNADMs was summarized. The impact of pH, DO, carbon source, and C/N on HNADMs growth and metabolism were discussed. In addition, the extracellular polymeric substance (EPS) production, quorum sensing (QS) secretion and P removal by HNADMs were displayed.

Enhanced nitrogen removal from low-temperature wastewater by an iterative screening of cold-tolerant denitrifying bacteria

The biological process to remove nitrogen in winter effluent is often seriously compromised due to the effect of low temperatures (< 13 °C) on the metabolic activity of microorganisms. In this study, a novel heterotrophic nitrifying-aerobic denitrifying bacterium with cold tolerance was isolated by iterative domestication and named Moraxella sp. LT-01. The LT-01 maintained almost 60% of its maximal growth activity at 10 °C. Under initial concentrations of 100 mg/L, the removal efficiencies of ammonium, nitrate, nitrite by LT-01 were 70.3%, 65.4%, 61.7% respectively for 72 h incubation at 10 °C. Nitrogen balance analysis showed that about 46% of TN was released as gases and 16% of TN was assimilated for cell growth. The biomarker genes involved in nitrification and denitrification pathways were identified by gene-specific PCR and revealed that the LT-01 has nitrite reductase (NirS) but not hydroxylamine reductase (HAO), which implies the involvement of other genes in the process. The study indicates that LT-01 has the potential for use in low-temperature regions for efficient sewage treatment.

Effect of bacteria-to-algae volume ratio on treatment performance and microbial community of a novel heterotrophic nitrification-aerobic denitrification bacteria-chlorella symbiotic system

A novel symbiotic system combined by heterotrophic nitrification-aerobic denitrification (HN-AD) mixed bacteria and Chlorella pyrenoidosa was firstly proposed to resolve the poor tolerance and nitrogen removal performance of traditional symbiotic system for treating high ammonia biogas slurry. Results showed that the volume ratio of bacteria to algae had significant effects on nitrogen removal efficiency, microbial community structure, functional bacteria and genes. The optimal ratio was 1/3, and the average removal efficiency of TN and TP increased by 28.9% and 67.6% respectively, compared to those of HN-AD bacteria. High-throughput sequencing indicated nitrogen removal was jointly completed by HN-AD and heterotrophic denitrification. HN-AD bacteria Halomonas and Pseudomonas played a key role in nitrogen removal, and Rhodocyclaceae and Paracoccus took an important part in phosphorus removal. According to the functional gene prediction, the total relative abundance of nitrogen removal genes (0.0127%) and narG, narH and narL genes (0.0054%) were highest in 1/3 system.

Dissimilatory nitrate reduction and functional genes in two subtropical rivers, China

Dissimilatory nitrate reduction processes, including denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA), are important pathways of nitrate transformation in the aquatic environments. In this study, we investigated potential rates of denitrification, anammox, and DNRA in the sediments of two subtropical rivers, Jinshui River and Qi River, with different intensities of human activities in their respective catchment, China. Our objectives were to assess the seasonality of dissimilatory nitrate reduction rates, quantify their respective contributions to nitrate reduction, and reveal the relationship between dissimilatory nitrate reduction rates, functional gene abundances, and physicochemicals in the river ecosystems. Our results showed higher rates of denitrification and anammox in the intensively disturbed areas in autumn and spring, and higher potential DNRA in the slightly disturbed areas in summer. Generally, denitrification, anammox, and DNRA were higher in summer, autumn, and spring, respectively. Relative contributions of nitrate reduction from denitrification, anammox, and DNRA were quite different in different seasons. Dissimilatory nitrate reduction rates and gene abundances correlated significantly with water temperature, dissolved organic carbon (DOC), sediment total organic carbon (SOC), NO₃^-, NH₄⁺, DOC/NO₃^-, iron ions, and sulfide. Understanding dissimilatory nitrate reduction is essential for restoring nitrate reduction capacity and improving and sustaining ecohealth of the river ecosystems.

Effects of design parameters, microbial community and nitrogen removal on the field-scale multi-pond constructed wetlands

Ecological multi-pond constructed wetlands (CWs) are an alternative wastewater treatment technology for nitrogen removal from non-point source pollution. As an important component of nitrogen cycles in the field-scale CWs, microorganisms are affected by design parameters. Nevertheless, the mechanism of design parameters affecting the distribution of microbial community and removal performance remains largely unexplored. In this study, satisfactory nitrogen removal performance was obtained in three multi-pond CWs. The highest mass removal rate per square meter (1104.0 mg/m²/day) and mass removal rate per cubic meter (590.2 mg/m³/day) for total nitrogen removal were obtained in the XY CW system during the wet season. The changes in seasonal parameters accounted for different removal performances and distributions of the microbial community. The combination of wastewater treatment technologies in the XY CW system consisting of ponds, CWs, and eco-floating treatment wetlands enriched the abundances of nitrogen-related functional genera. Correlation network analysis further demonstrated that longer hydraulic residence time and higher nitrogen concentration could intensify the enrichment of nitrogen-related functional genera. Regulating the combination of wastewater treatment technologies, the nitrogen concentration of influent, hydraulic loading rate, and water depth might promote the accumulation of microbial communities and enhance nitrogen removal. Macroscopical spatial/temporal regulation were proposed to enhance the treatment of non-point source pollution. The clarification of driving mechanism on design parameters, microbial community, and removal performance provided a novel perspective on the long-term maintenance of purification performance, practically sustainable applications, and scientific management of field-scale multi-pond CWs.

Mix-cultured aerobic denitrifying bacterial communities reduce nitrate: Novel insights in micro-polluted water treatment at lower temperature

Three mix-cultured aerobic denitrifiers were screened from a source water reservoir and named HE1, HE3 and SU4. Approximately 72.9%, 68.6% and 66.2% of nitrate were effectively removed from basal medium, respectively, after 120 h of cultivation at 8 °C. The nitrogen balance analysis revealed about one-fifth of the initial nitrogen was converted into gaseous denitrification products. According to the results of Biolog, the three microfloras had high metabolic capacity to carbon sources. The dominant genera were Pseudomonas and Paracoccus in these bacterial communities based on nirS gene sequencing. Response surface methodology elucidated that the denitrification rates of identified bacteria reached the maximum under the following optimal parameters: C/N ratio of 7.51-8.34, pH of 8.03-8.09, temperature of 18.03-20.19 °C, and shaking speed of 67.04-120 rpm. All results suggested that screened aerobic denitrifiers could potentially be applied to improve the source water quality at low temperature.

Characteristics and mechanism of heterotrophic nitrification/aerobic denitrification in a novel Halomonas piezotolerans strain

A strain was isolated from an activated sludge system and identified as Halomonas piezotolerans HN2 in this study, which is the first strain in H. piezotolerans with the capability of heterotrophic nitrification and aerobic denitrification. Strain HN2 showed the maximum nitrogen removal rate of 9.10 mg/L/h by utilizing ammonium at the salinity of 3.0%. Under saline environment, HN2 could remove nitrogen efficiently in neutral and slightly alkaline environments, with the carbon sources of sodium succinate and sodium citrate and the C/N ratio of 15-20, and the maximum removal efficiencies of ammonium, nitrite, and nitrate were 100%, 96.35%, and 99.7%, respectively. The genomic information revealed the presence of amoA, napA, and nosZ genes in strain HN2, and the target bands of nirS were obtained via a polymerase chain reaction. Therefore, we inferred that ammonium was mainly utilized for the growth of strain HN2 through assimilation, and another part of the initial ammonium was converted into nitrate through nitrification, and then into gaseous nitrogen through denitrification. This report indicated the potential application of strain HN2 and other nitrifying and denitrifying Halomonas strains in the removal of nitrogen pollution in marine-related environments and also implies the important role of Halomonas in the nitrogen cycle process of the ocean.

Mitigating NO and N2O emissions from a pilot-scale oxidation ditch using bioaugmentation of immobilized aerobic denitrifying bacteria

Nitrous oxide (N₂O) emission from wastewater treatment plants (WWTPs) requires urgent mitigation because of its significant contribution to the greenhouse effect. In this study, bioaugmentation was applied in a pilot-scale oxidation ditch with the aerobic denitrifying bacteria strain PCN-1 immobilized on polyurethane biocarriers, which demonstrated effective N₂O mitigation. Microbial community analysis suggested that the bioaugmentation facilitated a symbiotic relationship of the bacterial populations between the activated sludge and the biocarriers. The denitrifying bacteria with well-known N₂O reducing capabilities predominated on the biocarriers. Correspondingly, the increases of denitrifying genes and NO and N₂O reductase provided evidence for the enhanced genetic potential for NO and N₂O reduction. Besides, the enriched comammox Nitrospira on the biocarriers is proposed as another significant driver for N₂O mitigation by avoiding nitrite accumulation. In addition, the bioaugmentation enhanced the stability and recovery capability of the system in the ammonia overload and aeration failure shock tests.

Characteristics of a novel heterotrophic nitrification-aerobic denitrification yeast, Barnettozyma californica K1

Yeast strain K1, isolated from surface sediment, was identified as Barnettozyma californica. The strain showed efficient heterotrophic nitrification and aerobic denitrification (HN-AD) at initial ammonium, nitrite and nitrate concentrations of 14-140 mg/L. Additionally, the optimum carbon source for its growth and nitrogen removal activity was sucrose, followed by glucose, acetate and citrate. The maximum removal efficiencies of ammonium, nitrite and nitrate were 99.11%, 99.13% and 98.84% under 48 h of culture with sucrose at 140 mg/L nitrogen and the corresponding removal efficiencies of total nitrogen were 90.16%, 86.65% and 81.48%, respectively. The optimum conditions for the inorganic nitrogen removal and growth of strain K1 were a C/N of 18 and a salinity of 5-15 ppt. The amoA, nirK and nosZ genes of K1 were detected. All the results suggest that B. californica K1 is capable of HN-AD and has the potential to remove inorganic nitrogen from wastewater.

Nutrient removal from domestic wastewater: A comprehensive review on conventional and advanced technologies

Nitrogen and phosphorous are indispensable for growth and vitality of living beings, hence termed as nutrients. However, discharge of nutrient rich waste streams to aquatic ecosystems results in eutrophication. Therefore, nutrient removal from wastewater is crucial to meet the strict nutrient discharge standards. Similarly, nutrient recovery from waste streams is vital for the realization of a circular economy by avoiding the depletion of finite resources. This manuscript presents analysis of existing information on different conventional as well as advanced treatment technologies that are commonly practiced for the removal of nutrient from domestic wastewater. First, the information pertaining to the biological nutrient removal technologies are discussed. Second, onsite passive nutrient removal technologies are reviewed comprehensively. Third, advanced nutrient removal technologies are summarized briefly. The mechanisms, advantages, and disadvantages of these technologies along with their efficiencies and limitations are discussed. An integrated approach for simultaneous nutrient removal and recovery is recommended. The fifth section of the review highlights bottlenecks and potential solutions for successful implementation of the nutrient removal technologies. It is anticipated that the review will offer an instructive overview of the progress in nutrient removal and recovery technologies and will illustrate necessity of further investigations for development of efficient nutrient removal and recovery processes.

Biofilm producing indigenous bacteria isolated from municipal sludge and their nutrient removal ability in moving bed biofilm reactor from the wastewater

In the present study, improved moving bed biofilm reactor (MBBR) was applied to enhance the nutrient removal ability of the municipal wastewater. A total of 18 indigenous bacterial isolates were screened from the sewage sludge sample and nitrate reductase, nitrite reductase and hydroxylamine oxidase was analyzed. The strains Pseudomonas aeruginosa NU1 and Acinetobacter calcoaceticus K12 produced 0.87 ± 0.05 U/mg and 0.52 ± 0.12 U/mg hydroxylamine oxidase, 1.023 ± 0.062 U/mg and 1.29 ± 0.07 U/mg nitrite reductase, and 0.789 ± 0.031 U/mg and 1.07 ± 0.13 U/mg nitrate reductase. Nitrogen and phosphate removal improved by the addition of nutrient sources and achieved > 80% removal rate. pH and temperature of the medium also affected nutrient removal and improved removal was achieved at optimum level (p < 0.05). MBBR was designed with R1 (aerobic), R2 and R3 (anoxic) reactors. MBBR reactors removed acceptable level phosphorus removal properties up to 7.2 ± 3.8%, 42.4 ± 4.6%, and 84.2 ± 13.1% in the R1, R2, R3 and R4 reactors, respectively. Denitrification rate showed linear relationship at increasing concentrations nitrogen content in the reactor and denitrification rate was 1.43 g NO₂-N /m²/day at 1.5 g NO₂-N /m²/day. Dehydrogenase activity was assayed in all reactors and maximum amount was detected in the aerobic biofilm reactor. Based on the present findings, MBBRs and the selected bacterial strains are useful for the degradation domestic wastewater with minimum working area.