Comparison of moving bed biofilm reactor and bio-contact oxidation reactor start-up with heterotrophic nitrification-aerobic denitrification bacteria and activated sludge inoculation under high ammonia nitrogen conditions

To overcome poor ammonia tolerance and removal performance of bio-contact oxidation (BCO) reactor inoculated with activated sludge for high-ammonia nitrogen (NH4+-N) chemical wastewater treatment, this study compared inoculating heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria in moving bed biofilm reactor (MBBR) with activated sludge inoculation in BCO reactor under simulated high NH4+-N conditions. Results revealed that MBBR achieved faster biofilm formation (20 days vs. 100 days for BCO) with notable advantages: 27.6 % higher total nitrogen (TN) and 29.9 % higher NH4+-N removal efficiency than BCO. Microbial analysis indicated optimal enrichment of the key nitrogen removal (NR) bacterium Alcaligenes, leading to increased expression of NR enzymes hydroxylamine reductase, ensuring the superior NR efficiency of the MBBR. Additionally, functional enzymes and genes analysis speculated that the NR pathway in MBBR was: NH4+-N → NH2OH → NO3--N → NO2--N → NO → N2O → N2. This research offers a practical and theoretical foundation for extending HN-AD bacteria-inoculated MBBR processes.

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.

Dual-edged effects and mechanisms of hydroxylamine in partial denitrification-anaerobic ammonium oxidation system

The combination of partial denitrification (PD) and anaerobic ammonium oxidation (anammox) is a novel and promising nitrogen removal process. Regulating the synergistic reaction between denitrifiers and anammox bacteria (AnAOB) is the key to achieving stable and efficient PD-anammox performance. In this study, 10 mg/L of hydroxylamine (NH2OH) was considered to efficiently promote the bacterial activity, microbial energy flow, and the synergy of functional microflora. As a result, the nitrogen removal rate (NRR) significantly increased from 0.05 to 0.30 g N/L/d in parallel with an increase in the nitrogen loading rate (NLR) from 0.10 to 0.40 g N/L/d. However, the dual-edged effect of NH2OH was also confirmed. The long-term presence of NH2OH caused overgrowth of complete-denitrifying bacteria and decreased the NRR to 0.11 g N/L/d. Additionally, NH2OH enhanced nitrous oxide (N2O) emissions via chemical pathways as well as enhanced denitrification Fortunately, the inhibition caused by NH2OH was reversible by stopping the dosing, the reactor restored to stable operation with an NRR of 0.27 g N/L/d. Analysis of metabolic intensity and pathways revealed the effecting process and mechanism of NH2OH on the PD-anammox system. This study verified the dual-edged effects and mechanisms of NH2OH, therefore proving a theoretical basis and technical reference for the application of PD-anammox.

Nitrogen removal characteristics of heterotrophic nitrification-aerobic denitrification bacterium Acinetobacter ZQ-A1 and community characteristics analysis of its application in pig farm wastewater

A heterotrophic nitrifying aerobic denitrifying (HN-AD) strain ZQ-A1 with excellent denitrification performance, identified as Acinetobacter, was isolated from simultaneous nitrification and denitrification (SND) craft. ZQ-A1 was capable of removing NH4+, NO2-, and NO3-; the 21-hour removal rates were 84.84%, 87.13%, and 92.63%. ZQ-A1 has the ability to treat mixed nitrogen sources. In addition, ZQ-A1 can be well applied to actual sewage. According to the analysis of microbial community characteristics, the relative abundance of Acinetobacter in the experimental group increased from 0.06% to 2.38%, which is an important reason for the removal rate of NH4+ exceeding 99% within 30 days. The results of KEGG function prediction showed that with the addition of ZQ-A1, the relative abundance of pathways related to bacterial metabolism, such as tricarboxylic acid cycle metabolism, was higher. The research expanded the thinking of HN-AD bacteria in actual production and laid a foundation for its application in sewage treatment.

Insight into the roles of microalgae on simultaneous nitrification and denitrification in microalgal-bacterial sequencing batch reactors: Nitrogen removal, extracellular polymeric substances, and microbial communities

This study explored the influence and mechanism of microalgae on simultaneous nitrification and denitrification (SND) in microalgal-bacterial sequencing batch reactors (MB-SBR). It particularly focused on nitrogen transformation in extracellular polymeric substances (EPS) and functional groups associated with nitrogen removal. The results showed that MB-SBR achieved more optimal performance than control, with an SND efficiency of 68.01% and total nitrogen removal efficiency of 66.74%. Further analyses revealed that microalgae changed compositions and properties of EPS by increasing EPS contents and improving transfer, conversion, and storage capacity of nitrogen in EPS. Microbial community analysis demonstrated that microalgae promoted the enrichment of functional groups and genes related to SND and introduced diverse nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated the interactions between communities of bacteria and microalgae and the promotion of SND by microalgae as keystone connectors in the MB-SBR. This study provides insights into the roles of microalgae for enhanced SND.

Efficient nitrogen removal of a novel Pseudomonas chengduensis strain BF6 mainly through assimilation in the recirculating aquaculture systems

Biological nitrogen removal has received increasing attention in wastewater treatment. A bacterium with excellent nitrogen removal performance was isolated from biofilters of recirculating aquaculture systems (RAS) and identified as Pseudomonas chengduensis BF6. It was indicated that inorganic nitrogen is transformed into gaseous and biological nitrogen by the metabolic pathways of denitrification, anammox, and assimilation, which is the main nitrogen removal pathway of strain BF6. The strain BF6 could effectively remove nitrogen within 24 h under the conditions of ammonia, nitrate, nitrite, and mixed nitrogen sources with maximum total nitrogen removal efficiencies reaching 97.00 %, 61.40 %, 79.10 %, and 84.98 %, respectively. The strain BF6 exhibited total nitrogen removal efficiency of 91.14 %, altered the microbial diversity and enhanced the relative abundance of Pseudomonas in the RAS biofilter. These findings demonstrate that Pseudomonas sp. BF6 is a highly efficient nitrogen-removing bacterium with great potential for application in aquaculture wastewater remediation.

Genomics and nitrogen metabolic characteristics of a novel heterotrophic nitrifying-aerobic denitrifying bacterium Acinetobacter oleivorans AHP123

A novel aerobic strain of Acinetobacter oleivorans AHP123 was isolated from activated sludge, which could conduct heterotrophic nitrification and denitrification simultaneously. This strain has excellent NH₄⁺-N removal ability, with 97.93% removal rate at 24-hour. To identify the metabolic pathways of this novel strain, genes of gam, glnA, gdhA, gltB, nirB, nasA, nar, nor, glnK and amt were detected by genome analysis. Through RT-qPCR, it was found that the expression of key genes confirmed two possible ways of nitrogen removal in strain AHP123: nitrogen assimilation and heterotrophic nitrification aerobic denitrification (HNAD). However, the absence of some common HNAD genes (amo, nap and nos) suggested that strain AHP123 might have a different HNAD pathway from other HNAD bacteria. Nitrogen balance analysis revealed that strain AHP123 assimilated most of the external nitrogen sources into intracellular nitrogen.

Isolation and characteristics of two heterotrophic nitrifying and aerobic denitrifying bacteria, Achromobacter sp. strain HNDS-1 and Enterobacter sp. strain HNDS-6

In order to solve nitrogen pollution in environmental water, two heterotrophic nitrifying and aerobic denitrifying strains isolated from acid paddy soil were identified as Achromobacter sp. strain HNDS-1 and Enterobacter sp. strain HNDS-6 respectively. Strain HNDS-1 and strain HNDS-6 exhibited amazing ability to nitrogen removal. When (NH₄)₂SO₄, KNO₃, NaNO₂ were used as nitrogen resource respectively, the NH₄⁺-N, NO₃^--N, NO₂^--N removal efficiencies of strain HNDS-1 were 93.31%, 89.47%, and 100% respectively, while those of strain HNDS-6 were 82.39%, 96.92%, and 100%. And both of them could remove mixed nitrogen effectively in low C/N (C/N = 5). Strain HNDS-1 could remove 76.86% NH₄⁺-N and 75.13% NO₃^--N. And strain HNDS-6 can remove 65.07% NH₄⁺-N and 78.21% NO₃^--N. A putative ammonia monooxygenase, nitrite reductase, nitrate reductase, assimilatory nitrate reductase, nitrate/nitrite transport protein and nitric oxide reductase of strain HNDS-1, while hydroxylamine reductase, nitrite reductase, nitrate reductase, assimilatory nitrate reductase, nitrate/nitrite transport protein, and nitric oxide reductase of strain HNDS-6 were identified by genomic analysis. DNA-SIP analysis showed that genes Nxr, narG, nirK, norB, nosZ were involved in nitrogen removal pathway, which indicates that the denitrification pathway of strain HNDS-1 and strain HNDS-6 was NO₃^-→NO₂^-→NO→N₂O→N₂ during NH₄⁺-N removal process. And the nitrification pathway of strain HNDS-1 and strain HNDS-6 was NO₂^-→NO₃^-, but the nitrification pathway of NH₄⁺→ NO₂^- needs further studies.

Overlooked pathways of endogenous simultaneous nitrification and denitrification in anaerobic/aerobic/anoxic sequencing batch reactors with organic supplementation

The anaerobic/aerobic/anoxic (A/O/A) process is a promising biotechnology to intensify denitrification in low carbon/nitrogen (C/N) wastewater treatment, but the neglected typical rate-limiting step-nitrification-would hinder its wider application. Heterotrophic nitrification driven by intracellular carbon (PHAs) could enhance nitrification and achieve endogenous simultaneous nitrification and denitrification (ESND) in the A/O/A process, but its feasibility remains unexamined. Here we established four A/O/A-SBRs at different C/N ratios (3, 7.5, 12, and 16.5) to address the above-mentioned knowledge gaps. The results showed that organic supplementation promoted both nitrification and denitrification (performance and relevant enzymatic activities) until organic overdose (C/N = 16.5) exacerbated niche competitions from other non-functional heterotrophs. qPCR and batch tests indicated that high C/N ratios inhibited autotrophic nitrifiers, and heterotrophic nitrifiers (HNB) dominated in the enhanced nitrification. Given the high HNB contribution (43.7%) and low COD variation (< 10 mg L^-1) in the SND (76.4%) of CN12, we proposed a potential SND pathway based on heterotrophic nitrification and denitrification driven by PHAs and verified it with batch tests. Microbial and functional analyses suggested that CN12 favored the intracellular carbon transformation and harbored the minimum autotrophic nitrifiers, supporting the dominance of ESND in the enhanced SND. Our findings expand the understanding of the relationships between intracellular carbon transformation and SND and provide a novel nitrogen removal pathway for the practical application of the A/O/A process.

A novel Pseudomonas aeruginosa strain performs simultaneous heterotrophic nitrification-aerobic denitrification and aerobic phosphate removal

Nitrogen and phosphate removal from wastewater relies on different functional bacteria. In this study, a novel strain affiliated with Pseudomonas aeruginosa was isolated from activated sludge by gradient dilution and performed heterotrophic nitrification-aerobic denitrification and aerobic phosphate removal (HNADPR). The strain showed an ammonium removal efficiency of 87% and a phosphate removal efficiency of 97% under optimal conditions, such as C/N ratio of 10, P/N ratio of 0.1, temperature of 30°C, and pH of 7.5-8.5. The modified Gompertz model could fit well the heterotrophic ammonium nitrification, aerobic nitrite/nitrate denitrification, and aerobic phosphate removal processes. Functional gene amplification indicated that ammonium removal followed the complete HN-AD pathway (NH₄⁺ → NH₂OH → NO₂^- → NO₃^- → NO₂^- → NO → N₂O → N₂). Phosphate removal only occurred under aerobic conditions and ceased under anaerobic conditions. In successive aerobic cycles, the strain persistently took up phosphate. In wastewater, phosphate was aerobically converted into cell membrane, intracellular and extracellular polymeric substrates (EPS). Phosphorus in the form of phosphate monoester was pooled in EPS. A hypothetic aerobic phosphate removal model for strain SNDPR-01 is proposed to improve our understanding of the novel bacterial function of HNADPR.

Microbial composition and nitrogen removal pathways in a novel sequencing batch reactor integrated with semi-fixed biofilm carrier: evidence from a pilot study for low- and high-strength sewage treatment

The sequencing batch reactor (SBR) activated sludge process is a well-established technology for sewage treatment. One of the drawbacks of SBRs, however, total nitrogen (TN) removals is insufficient. By means of introducing four improvements, including semi-fixed biofilm carrier, sludge elevation mixing and change for the mode of influent and effluent, compliant standard for TN discharge was obtained in this novel SBR configuration during low- and high-strength sewage load. To illustrate the microbial compositions and functions of the attached biofilm on semi-fixed carrier and the suspended aggregates, as well as the nitrogen removal pathway, high throughput 16S rRNA gene amplicon sequencing, PICRUSt2 algorithm, and KEGG database were applied. The results revealed that (i) the microbial communities from suspended aggregates and biofilm samples were significantly different from each other; (ii) during low-strength sewage loads, TN removal was mainly by nitrification-denitrification. The suspended aggregates was responsible for denitrification, while the biofilm was focused on ammonium oxidation; (iii) during high-strength sewage loads, function of nitrate reductase from suspended aggregates was faded, and anammox and N assimilation by biofilm became dominant. Meanwhile, TN removal referring to the formation of L-glutamine via assimilation was the main pathway.

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.

Heterotrophic nitrification and aerobic denitrification by a novel Acinetobacter sp. TAC-1 at low temperature and high ammonia nitrogen

A novel strain was isolated from swinewastewater and identified as Acinetobacter sp. TAC-1 based on its phylogenetic and phenotypic characteristics. The strain TAC-1 was found to have a high ability to metabolize ammonium-N under low temperature condition. The strain TAC-1 could remove approximately 94.6% of ammonium-N (400 mg/L), 93.3% of nitrate-N (400 mg/L) and 42.4% of nitrite-N (400 mg/L) at 5 °C. The functional genes nitrate reductase gene (narG) and nitrite reductase gene (nirK, nirS) were successfully amplified by qPCR, further evidencing the heterotrophic nitrification and aerobic denitrification capability of Acinetobacter sp. TAC-1. The transcriptome data confirmed that the membrane transport protein and unsaturated fatty acid dehydrogenase-related genes of the strain TAC-1 were significantly up-regulated at 5 °C, enabling it to survive low temperatures. The high nitrogen removal ability at 5 °C makes this strain have a good application prospect.

Pathways regulating nitrogen removal in constructed ditch wetlands: effects of different inflow ratios and artificial aeration

Constructed ditch wetland (CDW) is a combination of idle ditch and constructed wetland, which is typically used in rural areas to remove pollutants from domestic wastewater. However, its low total nitrogen (TN) removal remains a pressing issue. To enhance total nitrogen removal, an approach of supplying water at two locations in the CDW at different influent flow ratios, combined with artificial aeration, was proposed to adjust carbon and oxygen distribution in the system. The highest average TN removal was achieved at low influent concentration (CDW4; influent flow ratio 1:2). The removal of TN in winter and spring were 58.93 and 83.26%, respectively. The distribution of carbon sources in the back zone enhanced denitrification. Of the high influent concentration treatments, CDW2 (2:1) achieved 16.97% more TN removal on average compared with CDW1 (3:0), after extra artificial aeration was applied in the front zone. However, nitrification was a limiting step in the system, which became the primary problem preventing pollutant purification. Moreover, nitrifying bacteria abundance was negatively correlated to the influent flow ratio and autotrophic denitrifying bacterial abundance was positively correlated to the influent flow ratios. Graphical abstract.

Nitrogen removal characteristics of a versatile heterotrophic nitrifying-aerobic denitrifying bacterium, Pseudomonas bauzanensis DN13-1, isolated from deep-sea sediment

A heterotrophic nitrifying-aerobic denitrifying bacterium isolated from deep-sea sediment was identified as Pseudomonas bauzanensis DN13-1. Nitrogen (N) removal capability and relative expression of nitrification and denitrification genes of this strain were investigated. The NO2--N, NO3--N and NH4+-N removal efficiencies were 98.82%, 65.87% and 98.89%, respectively, and strain DN13-1 could efficiently remove mixed N. Meanwhile, other inorganic N was not accumulated during these N removal processes. Genomic analysis indicated that genes nirS, norB, nosZ, nasA and putative amo were identified. The relative expression of functional genes by real-time PCR (qPCR) further confirmed nitrite, nitrate and ammonium removal pathways of strain DN13-1 under aerobic condition. Especially, the ammonium removal pathway of this strain was achieved through heterotrophic ammonium nitrification coupled with fast nitrite denitrification directly. Taken together, strain DN13-1 possesses particularity to efficiently remove N, which guarantees its promising application in aquaculture wastewater treatment.

Effects of COD/TN ratio on nitrogen removal efficiency, microbial community for high saline wastewater treatment based on heterotrophic nitrification-aerobic denitrification process

High salinity and high organic concentration impose negative impacts on autotrophic nitrification, which hinders efficient nitrogen removal. To achieve efficient nitrogen removal, high saline wastewater nitrogen removal systems with different COD/TN ratios based on heterotrophic nitrification-aerobic denitrification (HN-AD) process were established in this study. Results demonstrated that the COD/TN ratio had significant effects on nitrogen removal efficiency, microbial community structures and metabolic pathways. The optimal COD/TN ratio was 25 for nitrogen removal, with NH₄⁺-N and TN removal rates of 11.86 mg·L^-1·h^-1 and 11.50 mg·L^-1·h^-1, respectively (3.65 and 3.31 times higher than those COD/TN ratio of 10). 16S rRNA high-throughput sequencing revealed that HN-AD functional bacteria (Pseudomonas, Bacillus, Paracoccus) with highest abundance (7.61%) played a key role in high saline wastewater treatment. And Halomonas, Nitrincola and Oceanimonas participated in the denitrification process. Moreover, the abundance of genes related to nitrogen removal was the highest (1.90%) revealed by functional genes prediction.

Overlooked pathways of denitrification in a sulfur-based denitrification system with organic supplementation

Elemental sulfur-driven autotrophic denitrification (SADN) is a cost-effective approach for treating secondary effluent from wastewater treatment plants (WWTPs). Additional organics are generally supplemented to promote total nitrogen (TN) removal, reduce nitrite accumulation and sulfate production, and balance the pH decrease induced by SADN. However, understanding of the impacts of organic supplementation on microbial communities, nitrogen metabolism, denitrifier activity, and SADN rates in sulfur-based denitrification reactors is still limited. Here, a sulfur-based denitrification reactor was continuously operated for 272 days during which six different C/N ratios were tested successively (2.7, 1.5, 0.7, 0.5, 0.25, and 0). Organic supplementation improved TN removal and decreased NO₂^- accumulation, but reduced the relative abundance of denitrifiers and the contribution of autotrophic nitrate-reducing bacteria (aNRB) to TN removal during the long-term operation of reactor. Predictive functional profiling showed that nitrogen metabolism potential increased with decreasing C/N ratios. SADN was the predominant removal process when the C/N ratio was ≤0.7 (achieving 60% contribution when C/N = 0.7). Although organic supplementation weakened the dominant role of aNRB in denitrification, batch tests for the first time demonstrated that it could accelerate the SADN rate, attributed to the improvement of sulfur bioavailability, likely via the formation of polysulfide. A possible nitrogen removal pathway with multiple electron donors (i.e., sulfur, organics, sulfide, and polysulfide) in a sulfur-based denitrification reactor with organic supplementation was therefore proposed. However, supplementation with a high level of organics could increase the operational cost and effluent concentrations of sulfide and organics as well as enrich heterotrophic denitrifiers. Moreover, microbial community had substantial changes at C/N ratios of >0.5. Accordingly, an optimal C/N ratio of 0.25-0.5 was suggested, which could simultaneously minimize the additional operating cost associated with organic supplementation and maximize TN removal and SADN rates.

Nitrogen removal pathway and dynamics of microbial community with the increase of salinity in simultaneous nitrification and denitrification process

In this study, simultaneous nitrification and denitrification (SND) process was successfully established in a hybrid sequencing batch biofilm reactor (HSBBR). High removal efficiency of NH₄⁺-N (98.0±2.4% to 99.8±0.4%) and COD (86.6±4.0% to 91.6±1.8%) was observed in the salinity range of 0.0 to 2.4%. SND via nitrite, replacing SND via nitrate, became the main nitrogen removal pathway at 1.6% and 2.4% salinity. Suspended sludge and biofilm shared similar microbial composition. Dominant genera were substituted by salt-adaptable microbes as salinity increasing. Abundance of autotrophic ammonia-oxidizing bacteria (Nitrosomonas) increased with elevated salinity, while autotrophic nitrite-oxidizing bacteria (Nitrospira) exhibited extreme sensitivity to salinity. The presence of Gemmata demonstrated that heterotrophic nitrification co-existed with autotrophic nitrification in the SND process. Aerobic denitrifiers (Denitratisoma and Thauera) were also identified. Thiothrix, Sedimenticola, Sulfuritalea, Arcobacter (sulfide-based autotrophic denitrifier) and Hydrogenophaga (hydrogen-based autotrophic denitrifier) were detected in both S-sludge and biofilm. The occurrence of ANAMMOX bacteria Pirellula and Planctomyces indicated that ANAMMOX process was another pathway for nitrogen removal. Nitrogen removal in the HSBBR was accomplished via diverse pathways, including traditional autotrophic nitrification/heterotrophic denitrification, heterotrophic nitrification, aerobic and autotrophic denitrification, and ANAMMOX.

Effect of oxygen supply strategy on nitrogen removal of biochar-based vertical subsurface flow constructed wetland: Intermittent aeration and tidal flow

Insufficient dissolved oxygen (DO) concentration is recognized as one of the major factors limiting efficient nitrogen removal in constructed wetlands (CWs). This study investigated four biochar-based vertical subsurface flow constructed wetlands (VSFCWs) (system I: intermittent aeration without biochar addition; system II: intermittent aeration with biochar addition; system III: tidal flow without biochar addition; system IV: tidal flow with biochar addition) to compare the effect of oxygen supply strategies on the performance and mechanism of nitrogen removal. The results showed that NH₄⁺N removal efficiencies were 85.83%, 87.88%, 96.19%, and 98.30% for systems I-IV respectively. The abundance of microbes involved in nitrogen transformation also increased in all VSFCWs, particularly in the tidal flow mode with biochar addition. The higher oxygen utilization rate and higher surface area provided by biochar could significantly improve microbial abundance and then enhance nitrogen removal. Most notably, the rate of nitritation (2.92, 3.82, 3.14 and 4.27 mg N L^-1 h^-1) was higher than that of nitration (0.51, 0.66, 0.83 and 0.89 mg N L^-1 h^-1) in systems I-IV, respectively, and the percentages of NO₂^--N denitrified via simultaneous nitrification denitrification (SND) in systems I-IV were 58.20%, 55.10%, 50.89% and 51.89%, respectively. Therefore, in addition to conventional nitrification denitrification, partial nitrification and SND via NO₂^--N were also the significant nitrogen transformation pathways in the four VSFCWs at high DO concentrations (2.43-6.84 mg L^-1). These results demonstrated that the tidal flow biochar-based VSFCWs performed well in nitrogen removal due to efficient oxygen supplementation and enhanced microbial community abundance.

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.

Achieving short-cut nitrification and denitrification in modified intermittently aerated constructed wetland

This study aim to enhance nitrogen removal performance via shifting nitrogen removal pathway from nitrate to nitrite pathway. It was demonstrated that nitrite pathway was successfully and stably achieved in CWs by using modified intermittent aeration control with aeration 20min/non-aeration 100min and reducing DO concentration during aeration, nitrite in the effluent could accumulate to over 70% of the total oxidized nitrogen. Q-PCR analysis showed that nitrifying microbial communities were optimized under the alternating anoxic and aerobic conditions, ammonia oxidizing bacteria increased from 7.15×10⁶ to 8.99×10⁶copies/g, while nitrite oxidizing bacteria decreased approximately threefold after 234days operation. Most importantly, high nitrogen removal efficiency with ammonium removal efficiency of 94.6%, and total nitrogen removal efficiency of 82.6% could be achieved via nitrite pathway even under carbon limiting conditions. In comparison to the nitrate pathway, the nitrite pathway could improve the TN removal by about 55%.

Effect of plant-based carbon sources on denitrifying microorganisms in a vertical flow constructed wetland

The effects of supplementing plant-based carbon sources, fermented tissues of Arundo donax and Pontederia cordata, and a combination of the two plants, on the nitrogen removal efficiency and microbial composition in a vertical flow constructed wetland (VFCW) were examined. The results showed that the addition of the composite carbon source produced the highest removal efficiencies of NH₄⁺-N 91.5%, NO₃^--N 94.5% and TN 92.8% in VFCW. The detected abundance of amoA, nirS, and nxrA genes indicated that ammonia oxidation bacteria and denitrifying bacteria were more abundant than the nitrite oxidation bacteria. Furthermore, the addition of the composite carbon source significantly promoted the growth of the denitrifying bacteria in VFCW. The results indicated that supplementing the system with plant-based carbon sources achieved partial nitrification and denitrification, as well as classic denitrification in VFCWs. The study suggested that multiple nitrogen removal pathways were required to feasibly and efficiently remove nitrogen.

Heterotrophic nitrogen removal by a newly-isolated alkalitolerant microorganism, Serratia marcescens W5

A new microbe, Serratia marcescens W5 was successfully isolated. Its feasibility in purification of excessively nitrogen-containing wastewater was evaluated using inorganic nitrogen media. Single factor tests showed that W5 exhibited high ammonium removal rates (above 80%) under different culture conditions (pH 7-10, C/N ratios of 6-20, 15-35°C, 0-2.5% of salinity, respectively). Besides various organic carbon sources, W5 was able to utilize calcium carbonate with 28.05% of ammonium removed. Further experiments indicated that W5 was capable of resisting high-strength ammonium (1200mg/L) with the maximum removal rate of 514.13mgL(-1)d(-1). The nitrogen removal pathway of W5 was also tested, showing that both nitrite and nitrate were efficiently removed only in the presence of ammonium, with hydroxylamine as intermediate, which was different from the conventional nitrogen removal pathway. All the results verified that W5 was a good candidate for the purification of excessively nitrogenous wastewater.

Microbial nitrogen removal pathways in integrated vertical-flow constructed wetland systems

Microbial nitrogen (N) removal pathways in planted (Canna indica L.) and unplanted integrated vertical-flow constructed wetland systems (IVCWs) were investigated. Results of, molecular biological and isotope pairing experiments showed that nitrifying, anammox, and denitrifying bacteria were distributed in both down-flow and up-flow columns of the IVCWs. Further, the N transforming bacteria in the planted IVCWs were significantly higher than that in the unplanted ones (p<0.05). Moreover, the potential nitrification, anammox, and denitrification rates were highest (18.90, 11.75, and 7.84nmolNg(-1)h(-1), respectively) in the down-flow column of the planted IVCWs. Significant correlations between these potential rates and the absolute abundance of N transformation genes further confirmed the existence of simultaneous nitrification, anammox, and denitrification (SNAD) processes in the IVCWs. The anammox process was the major N removal pathway (55.6-60.0%) in the IVCWs. The results will further our understanding of the microbial N removal mechanisms in IVCWs.

The characteristics of a novel heterotrophic nitrifying and aerobic denitrifying bacterium, Acinetobacter junii YB

A novel heterotrophic nitrifying bacterium was isolated from activated sludge and was identified as Acinetobacter junii YB. The strain exhibited efficient heterotrophic nitrification-aerobic denitrification ability at a broad range of ammonium loads and had the capability to utilize hydroxylamine, nitrite and nitrate as a sole nitrogen source. Based on the nitrogen removal and enzyme assay, the nitrogen removal pathway was speculated to be achieved through heterotrophic nitrification coupled with aerobic denitrification. In addition, single-factor experiments showed that efficient heterotrophic nitrification and growth of strain YB occurred with succinate as the carbon source, pH 7.5, 37 °C, and high C/N ratio and dissolved oxygen. Furthermore, the new isolate showed capacities for aggregation and hydrophobicity. Regular variations of the flocculating ability and relative hydrophobicity were observed during the whole cultivation. The ability to perform heterotrophic nitrification-aerobic denitrification and cell aggregation demonstrated the great potential of the strain YB for future applications.