Nitrogen removal characteristics of efficient heterotrophic nitrification-aerobic denitrification bacterium and application in biological deodorization

Characterization and genomic insights into the nitrogen metabolism of heterotrophic nitrifying and aerobic denitrifying bacterium Pseudomonas aeruginosa WS-03

To achieve effective removal of various inorganic nitrogen in aquatic ecosystems, while expanding the applicability of existing heterotrophic nitrifying-aerobic denitrifying (HN-AD) strains and enhancing their stress tolerance, we isolated the Pseudomonas aeruginosa WS-03 from a sewage treatment plant. The results of parameter optimization indicated that the following were the most favorable conditions for nitrogen removal: using sodium citrate as the carbon source, a C/N ratio of 9, a pH of 7, a temperature of 30 °C and an NH4+-N concentrations below 300 mg/L. The maximum reduction rates of nitrogen are 8.96 mg/(L·h), 4.64 mg/(L·h) and 5.12 mg/(L·h) of NH4+-N, NO3--N and TN, respectively. The result of genome analysis and polymerase chain reaction (PCR) amplification electrophoresis revealed the presence of genes related to nitrogen metabolism, which involves nitrification, denitrification, and assimilation pathways. It also verified that absence of key nitrification genes in strain WS-03, suggesting it operates via a unique denitrification mechanism. Notably, nitrogen assimilation has been identified as the predominant pathway for nitrogen removal by the strain. The strain demonstrated an impressive efficiency of 54.28% in reducing the concentration of NH4+-N in untreated landfill leachate, highlighting its potential for application in practical wastewater treatment. This study comprehensively explored the denitrification characteristics and showed its significant role in environmental remediation.

New Insight Into the Mechanism of Nitrite Enhancement on Heterotrophic Nitrification and Aerobic Denitrification Bacterium in Gene Expression

The growth and nitrogen metabolism of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria are affected by nitrite, but the mechanisms underlying this for strain Acinetobacter johnsonii EN-J1 are unclear. In this study, the addition of 10 mg/L nitrite increased the reduction rate of ammonium by 1.0 mg/L/h, and 20 mg/L nitrite increased the reduction rate of nitrate by 3.9 mg/L/h. Compared with the control, the nitrate reductase activity, electron transfer activity, and adenosine triphosphate content of EN-J1 were enhanced by 142.0%, 278.0% and 279.0%, respectively, in the nitrate removal process after the addition of 20 mg/L nitrite. The whole genome was annotated with nitrogen removal genes such as narGHI, narK, nsrR, nirBD, nasA, glnA, gltB, gdhA and amt. Transcriptome analysis showed that nitrite triggered significant upregulation of several key pathways, including nitrogen metabolism, the tricarboxylic acid cycle, and amino acid metabolism for enhancing denitrification. The expression of key denitrification genes (narG, narK, hmp, nirBD, glnA and nasA) was detected by real-time quantitative polymerase chain reaction. These results suggested that nitrite enhances denitrification by increasing the expression of denitrification genes, electron transfer and adenosine triphosphate levels, which is important for elucidating the mechanism of nitrite promotion of biological nitrogen removal efficiency.

Characteristics of a heavy metal resistant heterotrophic nitrification-aerobic denitrification bacterium isolated from municipal activated sludge

The heterotrophic nitrification-aerobic denitrification (HNAD) is a new biological denitrification technology, the present study isolated a new HNAD strain named Cupriavidus metallidurans TX6 with heavy metal resistance. The gene expression, electron transport, enzyme activity and nitrogen removal property of strain TX6 were studied with different influencing factors. Strain TX6 has five nitrogen metabolism pathways (NH4+ → NH2OH → NO → NO2- → NH4+ → GOGAT/GDH; NH4+-N → NH2OH → NO → N2O → N2; NH4+ → NH2OH → NO → NO2- → NO3-; NO3- → NO2- → NH4+ → GOGAT/GDH; NO3-→ NO2- → NH4+ → GOGAT/GDH). Nitrogen balance analysis shows that 29 ± 4 mg/L of N was converted to intracellular nitrogen by assimilation and 50 ± 3 mg/L N loss may be attributed to aerobic denitrification. The results provide a theoretical basis for the HAND bacteria application in nitrogen removal from wastewaters containing heavy metals.

Efficient strategy for employing HN-AD bacterium enhanced biofilter reactors to remove NH3 and reduce secondary pollution

Heterotrophic nitrification-aerobic denitrification (HN-AD) strain (Paracoccus denitrificans HY-1) was employed in this study to enhance the removal efficiency of NH3 in a biological trickling filter (BTF) reactor. The results demonstrated that inoculation with HY-1 and packed with bamboo charcoal as filler significantly improved the RE of NH3 in BTF, reaching 96.52 % under 27 s of empty bed residence time (EBRT) and 812.56 ppm of inlet gas concentration. Meanwhile, the titer of NH4+-N, NO2--N, and NO3--N in the circulating fluid were merely 8.52 mg/L, 5.14 mg/L, and 18.07 mg/L, respectively. Microbial community and metabolism analyses revealed that HY-1 have successfully colonized in the BTF, and the high expression of denitrification-related genes (nar, nap, nir, nor and nos) further confirmed that the inoculation of HY-1 greatly improved both nitrification and denitrification metabolism. Furthermore, the biofilter reactor inoculated with HY-1 was applied at a large-scale piggery and exhibited remarkable odor removal effect, in which 99.61 % of NH3 and 96.63 % of H2S were completely eliminated. In general, the HN-AD bacterium could strengthen the performance of BTF reactor and reduce the secondary pollution of circulating fluid during bio-deodorization.

The mechanism of survival and degradation of phenol by Acinetobacter pittii in an extremely acidic environment

The treatment efficiency of acidic phenol-containing wastewater is hindered by the absence of efficient acid-resistant phenol-degrading bacteria, and the acid-resistant mechanism of such bacteria remains poorly studied. In this study, the acid-resistant strain Hly3 was used as a research model to investigate its ability to degrade phenol and its underlying mechanism of acid resistance. Strain Hly3 exhibited robust acid resistance, capable of surviving in extremely acidic environments (pH 3) and degrading 1700 mg L-1 phenol in 72 h. Through the physiological response analysis of strain Hly3 to pH, the results indicated: firstly, the strain could reduce the relative permeability of the cell membrane and increase EPS secretion to prevent H+ from entering the cell (shielding effect); secondly, the strain could accumulate more buffering substances to neutralize the intracellular H+ (neutralization effect); thirdly, the strain could expel H+ from the cell by enhancing H+-ATPase activity (pumping effect); finally, the strain produced more active scavengers to reduce the toxicity of acid stress on cells (antioxidant effect). Subsequently, combining liquid chromatography-mass spectrometry (LC-MS) technology with exogenous addition experiments, it was verified that the acid resistance mechanism of microorganisms is achieved through the activation of acid-resistant response systems by glutamine, thereby enhancing functions such as shielding, neutralization, efflux, and antioxidation. This study elucidated the acid resistance mechanism of Acinetobacter pittii, providing a theoretical basis and guidance for the treatment of acidic phenol-containing wastewater.

Efficient nitrogen removal via simultaneous ammonium assimilation and heterotrophic denitrification of Paracoccus denitrificans R-1

Although diverse microorganisms can remove ammonium and nitrate simultaneously, their metabolic mechanisms are not well understood. Paracoccus denitrificans R-1 showed the maximal NH4 + removal rate 9.94 mg L-1·h-1 and 2.91 mg L-1·h-1 under aerobic and anaerobic conditions, respectively. Analysis of the nitrogen balance calculation and isotope tracing experiment indicated that NH4 + was consumed through assimilation. The maximal NO3 - removal rate of strain R-1 was 18.05 and 19.76 mg L-1·h-1 under aerobic and anaerobic conditions, respectively. The stoichiometric consumption ratio of acetate to nitrate was 0.902 and NO3 - was reduced to N2 for strain R-1 through 15NO3 - isotopic tracing experiment, which indicated a respiratory process coupled with the oxidation of electron donors. Genomic analysis showed that strain R-1 contained genes for ammonium assimilation and denitrification, which effectively promoted each other. These findings provide insights into microbial nitrogen transformation and facilitate the simultaneous removal of NH4 + and NO3 - in a single reactor.

Optimal conditions and nitrogen removal performance of aerobic denitrifier Comamonas sp. pw-6 and its bioaugmented application in synthetic domestic wastewater treatment

To assess the possibility of using aerobic denitrification (AD) bacteria with high NO2--N accumulation for nitrogen removal in wastewater treatment, conditional optimization, as well as sole and mixed nitrogen source tests involving AD bacterium, Comamonas sp. pw-6 was performed. The results showed that the optimal carbon source, pH, C/N ratio, rotational speed, and salinity for this strain were determined to be succinate, 7, 20, 160 rpm, and 0%, respectively. Further, this strain preferentially utilized NH4+-N, NO3--N, and NO2--N, and when NO3--N was its sole nitrogen source, 92.28% of the NO3--N (150 mg·L-1) was converted to NO2--N. However, when NH4+-N and NO3--N constituted the mixed nitrogen source, NO3--N utilization by this strain was significantly lower (p < 0.05). Therefore, a strategy was proposed to combine pw-6 bacteria with traditional autotrophic nitrification to achieve the application of pw-6 bacteria in NH4+-N-containing wastewater treatment. Bioaugmented application experiments showed significantly higher NH4+-N removal (5.96 ± 0.94 mg·L-1·h-1) and lower NO3--N accumulation (2.52 ± 0.18 mg·L-1·h-1) rates (p < 0.05) than those observed for the control test. Thus, AD bacteria with high NO2--N accumulation can also be used for practical applications, providing a basis for expanding the selection range of AD strains for wastewater treatment.

Extracellular electron transfer for aerobic denitrification mediated by the bioelectric catalytic system with zero-carbon source

The slow rate of electron transfer and the large consumption of carbon sources are technical bottlenecks in the biological treatment of wastewater. Here, we first proposed to domesticate aerobic denitrifying bacteria (ADB) from heterotrophic to autotrophic by electricity (0.6 V) under zero organic carbon source conditions, to accelerate electron transfer and shorten hydraulic retention time (HRT) while increasing the biodegradation rate. Then we investigated the extracellular electron transfer (EET) mechanism mediated by this process, and additionally examined the integrated nitrogen removal efficiency of this system with composite pollution. It was demonstrated that compared with the traditional membrane bioreactor (MBR), the BEC displayed higher nitrogen removal efficiency. Especially at C/N = 0, the BEC exhibited a NO3--N removal rate of 95.42 ± 2.71 % for 4 h, which was about 6.5 times higher than that of the MBR. Under the compound pollution condition, the BEC still maintained high NO3--N and tetracycline removal (94.52 ± 2.01 % and 91.50 ± 0.001 %), greatly superior to the MBR (10.64 ± 2.01 % and 12.00 ± 0.019 %). In addition, in-situ electrochemical tests showed that the nitrate in the BEC could be directly converted to N2 by reduction using electrons from the cathode, which was successfully demonstrated as a terminal electron acceptor.

Enhancement strategies of aerobic denitrification for efficient nitrogen removal from low carbon-to-nitrogen ratio shale oil wastewater

The strategy of high reflux ratio and long solids retention time was adopted to realize efficient nitrogen removal from real shale oil wastewater. This was undertaken with a low chemical oxygen demand to total nitrogen (COD/TN) ratio by strengthening aerobic denitrification in an anoxic/aerobic membrane bioreactor (A/O-MBR). The TN removal load climbed from 22 to 25 g N/(kg MLSS·d) as the COD/TN ratio declined from 8 to 3. The abundance of heterotrophic nitrifying and aerobic denitrifying (HNAD) bacteria increased by 13.8 times to 42.5%, displacing anoxic denitrifying bacteria as the predominant bacteria. The abundance of genes involved in denitrification (napAB, narGHI, norBC, nosZ) increased, however the genes related to assimilatory nitrate reduction (nirA, narB, nasC) decreased. The capacity of the dominant HNAD bacteria in an A/O-MBR to efficiently utilize a carbon source is the key to efficient nitrogen removal from shale oil wastewater with a low COD/TN ratio.

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.

Bioaugmentation of woodchip bioreactors by Pseudomonas nicosulfuronedens D1-1 with functional species enrichment

A novel heterotrophic nitrification and aerobic denitrification (HN-AD) bacterium D1-1 was identified as Pseudomonas nicosulfuronedens D1-1. Strain D1-1 removed 97.24%, 97.25%, and 77.12% of 100 mg/L NH₄⁺-N, NO₃^--N, and NO₂^--N, with corresponding maximum removal rates of 7.42, 8.69, and 7.15 mg·L^-1·h^-1, respectively. Strain D1-1 bioaugmentation enhanced woodchip bioreactor performance with an average NO₃^--N removal efficiency of 93.8%. Bioaugmentation enriched N cyclers along with increased bacterial diversity and predicted genes for denitrification, DNRA (dissimilatory nitrate reduction to ammonium), and ammonium oxidation. It also reduced local selection and network modularity from 4.336 to 0.934, resulting in predicted nitrogen (N) cycling genes shared by more modules. These observations suggested that bioaugmentation could enhance the functional redundancy to stabilize the NO₃^--N removal performance. This study provides insights into the potential applications of HN-AD bacteria in bioremediation or other environmental engineering fields, relying on their ability to shape bacterial communities.

Three Novel Marine Species of Paracoccus, P. aerodenitrificans sp. nov., P. sediminicola sp. nov. and P. albus sp. nov., and the Characterization of Their Capability to Perform Heterotrophic Nitrification and Aerobic Denitrification

Heterotrophic nitrification-aerobic denitrification (HN-AD) is an efficient nitrogen removal process and the genus Paracoccus is one important group of the HN-AD bacteria. During an investigation of the microbial diversity in marine ranching of the Pearl River Estuary (PR China), three bacterial strains, designated SCSIO 75817^T, SCSIO 76264^T and SCSIO 80058^T, were isolated from sediments. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the three strains belonged to the genus Paracoccus and their closest neighbors were P. isoporae DSM 22220^T (97.6-98.0%), P. aurantiacus CGMCC 1.13898^T (97.3-97.6%) and P. xiamenensis MCCC 1A16381^T (97.1-97.4%), respectively. The analysis results of 16S rRNA gene similarity, ANI, AAI and dDDH showed that the pairwise similarities between these three strains and their closest neighbors were 97.4-98.5%, 76.9-81.0%, 75.5-79.6% and 20.3-23.3%, respectively. Polyphasic taxonomic data of the phylogenetic, phenotypic and chemotaxonomic analyses indicate that these strains represent three novel species in the genus Paracoccus, for which the names Paracoccus aerodenitrificans sp. nov., Paracoccus sediminicola sp. nov. and Paracoccus albus sp. nov. are proposed, respectively. The study also demonstrated the heterotrophic nitrification-aerobic denitrification (HN-AD) ability of the novel species P. aerodenitrificans SCSIO 75817^T. When it was aerobically cultivated at 28 °C using NH₄⁺-N, NO₃^--N and NO₂^--N as the sole nitrogen sources, the nitrogen removal efficiencies were 73.4, 55.27 and 49.2%, respectively, and the maximum removal rates were 3.05, 1.82 and 1.63 mg/L/h, respectively. The results suggest that it has promising potential for wastewater treatment.

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.