Removal of ammonium in surface water at low temperature by a newly isolated Microbacterium sp. strain SFA13

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.

Efficient degradation of venlafaxine using intimately coupled high-active crystal facets exposed TiO2 and biodegradation system: Kinetic studies, biofilm stress behavior and transformation mechanism

Intimately coupled photocatalysis and biodegradation (ICPB) system is a potential wastewater treatment technology, of which TiO2-based ICPB system has been widely studied. There are many ways to improve the degradation efficiency of the ICPB process, but no crystal facet engineering method has been reported yet. In this work, a new ICPB system coated with NaF-TiO2 exposing high energy facets was designed to degrade biorecalcitrant psychotropic drug - venlafaxine (VNF). Initially, the TiO2 crystal surface was modified with NaF, resulting in the formation of NaF-TiO2 with a 14.4% increase in the exposure ratio of (001). The contribution rate of ·OH was increased by 9.5%, and the contribution rate of h+ was increased by 33.2%. Next, NaF-TiO2 was loaded onto the surface of the sponge carrier, and then the ICPB system was constructed after about 15 days of biofilm formation. After the ICPB system was acclimated with VNF, the removal rate of COD decreased significantly (the lowest was 62.7%), but that of ammonia nitrogen remained at 50.5 ± 6.0% and the extracellular polymeric substance (EPS) secretion increased by 84.1 mg/g VSS. According to the high throughput results, at the phylum level, Proteobacteria and Chloroflexi together maintain the nitrogen removal capability and structural stability of the ICPB system. The relative abundance of Bacteroidota was significantly increased by 14.2%, suggesting that there may be some correlation between Bacteroidota and certain metabolites of the anti-depressant active ingredients. At the genus level, the Thauera (3.1%∼11.5%) is the major bacterial group that secretes EPS, protecting biofilm against external influences. Most of the changes in microorganisms are consistent with the decontamination properties and macroscopic appearance of EPS in the ICPB system. Finally, the degradation efficiency of ICPB system for VNF was investigated (92.7 ± 3.8%) and it was mostly through hydroxylation and demethylation pathways, with more small molecular products detected, providing the basis for biological assimilation of VNF. Collectively, the NaF-TiO2 based ICPB system would be lucrative for the future degradation of venlafaxine.

C4-HSL-mediated quorum sensing regulates nitrogen removal in activated sludge process at Low temperatures

The activated sludge process faces challenges in achieving adequate nitrification ability under low-temperature conditions. Therefore, we investigated the effects of different concentrations of exogenous N-butyryl-homoserine lactone (C4-HSL) on nitrogen removal in lab-scale sequencing batch reactors (SBRs) at 10 °C. The results revealed that both 10 and 100 μg/L of C4-HSL could improve NH4+-N removal efficiency by 26% and reduce the effluent TN concentration to below 15 mg/L. Analysis of extracellular polymeric substances (EPS) revealed that adding C4-HSL (especially 100 μg/L) reduced the protein-like substance content while increasing the humic and fulvic acid-like substance content in EPS. Protein-like substances could serve as carbon sources for denitrifiers, thus promoting denitrification. Moreover, exogenous C4-HSL increased the abundance of bacteria and genes associated with nitrification and denitrification. Further analysis of quorum sensing (QS) of microorganisms indicated that exogenous C4-HSL (especially 100 μg/L) promoted regulation, transportation, and decomposition functions in the QS process. Furthermore, CS, sdh, fum, and mdh gene expressions involved in the tricarboxylic acid (TCA) cycle were enhanced by 100 μg/L C4-HSL. Exogenous C4-HSL promoted microbial communication, microbial energy metabolism, and nitrogen metabolism, thereby improving the nitrogen removal efficiency of activated sludge systems at low temperatures. This study provides a feasible strategy for enhancing denitrogenation performance at low temperatures through exogenous C4-HSL.

Mechanisms of ammonia, calcium and heavy metal removal from nutrient-poor water by Acinetobacter calcoaceticus strain HM12

An Acinetobacter calcoaceticus strain HM12 capable of heterotrophic nitrification-aerobic denitrification (HN-AD) under nutrient-poor conditions was isolated, with an ammonia nitrogen (NH4+-N) removal efficiency of 98.53%. It can also remove heavy metals by microbial induced calcium precipitation (MICP) with a Ca2+ removal efficiency of 75.91%. Optimal conditions for HN-AD and mineralization of the strain were determined by kinetic analysis (pH = 7, C/N = 2.0, Ca2+ = 70.0 mg L-1, NH4+-N = 5.0 mg L-1). Growth curves and nitrogen balance elucidated nitrogen degradation pathways capable of converting NH4+-N to gaseous nitrogen. The analysis of the bioprecipitation showed that Zn2+ and Cd2+ were removed by the MICP process through co-precipitation and adsorption (maximum removal efficiencies of 93.39% and 80.70%, respectively), mainly ZnCO3, CdCO3, ZnHPO4, Zn3(PO4)2 and Cd3(PO4)2. Strain HM12 produces humic and fulvic acids to counteract the toxicity of pollutants, as well as aromatic proteins to increase extracellular polymers (EPS) and promote the biomineralization process. This study provides a experimental evidence for the simultaneous removal of multiple pollutants from nutrient-poor waters.

Systematic investigation of simultaneous copper biosorption and nitrogen removal from wastewater by an aerobic denitrifying bacterium of auto-aggregation

Finding effective methods for simultaneous removal of eutrophic nutrients and heavy metals has attracted increasing concerns for the environmental remediation. Herein, a novel auto-aggregating aerobic denitrifying strain (Aeromonas veronii YL-41) was isolated with capacities for copper tolerance and biosorption. The denitrification efficiency and nitrogen removal pathway of the strain were investigated by nitrogen balance analysis and amplification of key denitrification functional genes. Moreover, the changes in the auto-aggregation properties of the strain caused by extracellular polymeric substances (EPS) production were focused on. The biosorption capacity and mechanisms of copper tolerance during denitrification were further explored by measuring changes in copper tolerance and adsorption indices, as well as by variations in extracellular functional groups. The strain showed extremely strong total nitrogen removal ability, with 67.5%, 82.08% and 78.48% of total nitrogen removal when NH4+-N, NO2--N, and NO3--N were used as the only initial nitrogen source, respectively. The successful amplification of napA, nirK, norR, and nosZ genes further demonstrated that the strain accomplished nitrate removal through a complete aerobic denitrification pathway. The production of protein-rich EPS of up to 23.31 mg/g and an auto-aggregation index of up to 76.42% may confer a strong biofilm-forming potential to the strain. Under the stress of 20 mg/L copper ions, the removal of nitrate-nitrogen was still as high as 71.4%. In addition, the strain could achieve an efficient removal of 96.9% of copper ions at an initial concentration of 80 mg/L. Scanning electron microscopy and deconvolution analysis of characteristic peaks confirmed that the strains encapsulate heavy metals by secreting EPS and, meanwhile, form strong hydrogen bonding structures to enhance intermolecular forces to resist copper ion stress. This study provides an innovative and effective biological approach for the synergistic bioaugmentation removal of eutrophic substances and heavy metals from aquatic environments.

Removal of ammonium and manganese from surface water using a MeOx filter system as a pretreatment process

Residual aluminium from the coagulation-sedimentation process in the treatment of surface water can decrease the catalytic activity of a manganese co-oxide filter film (MeO_x) used for ammonium and manganese removal. To solve this problem, a MeO_x filter was used as a pretreatment process to filtrate source water directly before the coagulation and sedimentation treatment. The removal performance and the mechanism of change in the activity of MeO_x were investigated. The experimental results indicated that the MeO_x filter removed ammonium and manganese from surface water sources effectively, and its manganese removal activity was enhanced. The characteristics of MeO_x were investigated via SEM, EDS, XPS, and the BET surface area. Analysis of the experimental results showed that the increase in the content of Al under this condition was much lower than that under treatment with the coagulation-sedimentation process. After long-term operation, the amount and surface area of MeO_x coated on the filter sand increased significantly, leading to an increase in the catalytic activity. However, in cold water, the catalytic activity of MeO_x decreased, and more Mn(II) was obtained on the surface of MeO_x. Thus, the morphology of MeO_x changed. Fortunately, when water temperature increases, the removal activity can recover immediately. By inactivating microorganisms and comparing the removal performance with that under other conditions, the MeO_x activity of the pretreatment process is preserved effectively and no strengthening measures are required. This study will provide a new strategy for the use of the MeO_x catalytic technology.

Tea biochar-immobilized Ralstonia Bcul-1 increases nitrate nitrogen content and reduces the bioavailability of cadmium and chromium in a fertilized vegetable soil

Pyrolytic biochar (PL-BC, pyrochar) and hydrothermal biochar (HT-BC, hydrochar) derived from branches and leaves of tea plants had different pH, electrical conductivity (EC), total carbon nitrogen content, BET surface area, total pore volume, average pore diameter, and functional groups. HT-BC had a larger specific surface area and more functional groups than PL-BC. Ralstonia Bcul-1 (R-B) was the dominant and functional bacteria in a fertilized vegetable soil supplemented with TBB-immobilized R-B (TBB + R-B). R-B vitality was more closely related to BET surface area, total pore volume, and functional groups of tea-based biochar (TBB: PL-BC and HT-BC). R-B was able to maintain high oxidase activity. R-B and TBB + R-B can increase the activities of urease and peroxidase in vegetable soil playing an essential role in the biotransformation of ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N). TBB was able to simultaneously increase the content of NO₃^--N and NH₄⁺-N, and TBB + R-B also significantly increased NO₃^--N content but decreased NH₄⁺-N content in a fertilized vegetable soil. These results indicated that R-B promoted nitrification in the soil, i.e. conversion of NH₄⁺-N into NO₃^--N, by enhancing the activities of urease and peroxidase. R-B had high adsorption capacity for cadmium (Cd) and chromium (Cr) (Cd&Cr: Cd and Cr). Moreover, TBB + R-B was able to convert weak acid extractable and reducible Cd&Cr into a more stable residual fraction and oxidizable Cd&Cr. The overall effect of the treatments was to reduce plant uptake of Cd&Cr by cabbage. TBB + R-B significantly promoted R-B growth, changed inorganic nitrogen speciation, increased NO₃^--N supply, reduced Cd&Cr bioavailability, and decreased plant tissue Cd&Cr content.

Nitrogen-metabolising microorganism analysis in rapid sand filters from drinking water treatment plant

Sand filters (SFs) are common treatment processes for nitrogen pollutant removal in drinking water treatment plants (DWTPs). However, the mechanisms on the nitrogen-cycling role of SFs are still unclear. In this study, 16S rRNA gene amplicon sequencing was used to characterise the diversity and composition of the bacterial community in SFs from DWTPs. Additionally, metagenomics approach was used to determine the functional microorganisms involved in nitrogen cycle in SFs. Our results showed that Pseudomonadota, Acidobacteria, Nitrospirae and Chloroflexi dominated in SFs. Subsequently, 85 high-quality metagenome-assembled genomes (MAGs) were retrieved from metagenome datasets of selected SFs involving nitrification, assimilatory nitrogen reduction, denitrification and anaerobic ammonia oxidation (anammox) processes. Read mapping to reference genomes of Nitrospira and the phylogenetic tree of the ammonia monooxygenase subunit A gene, amoA, suggested that Nitrospira is abundantly found in SFs. Furthermore, according to their genetic content, a nitrogen metabolic model in SFs was proposed using representative MAGs and pure culture isolate. Quantitative real-time polymerase chain reaction (qPCR) showed that ammonia-oxidising bacteria (AOB) and archaea (AOA), and complete ammonia oxidisers (comammox) were ubiquitous in the SFs, with the abundance of comammox being higher than that of AOA and AOB. Moreover, we identified a bacterial strain with a high NO₃-N removal rate as Pseudomonas sp. DW-5, which could be applied in the bioremediation of micro-polluted drinking water sources. Our study provides insights into functional nitrogen-metabolising microbes in SFs of DWTPs.

Insight into the Cold Adaptation Mechanism of an Aerobic Denitrifying Bacterium: Bacillus simplex H-b

Psychrophilic bacteria with aerobic denitrification ability have promising potential for application in nitrogen-contaminated wastewater treatment, especially under cold conditions. A better understanding of the cold adaptation mechanism during aerobic denitrification would be beneficial for the practical application of this type of functional bacterium. In this study, Bacillus simplex H-b with good denitrification performance at 5°C was used to investigate the corresponding cold tolerance mechanism. Transcriptomics and nitrogen removal characterization experiments were conducted at different temperatures (5°C, 20°C, and 30°C). At low temperatures, more nitrogen was utilized for assimilation, accompanied by the accumulation of ATP and extracellular polymeric substances (EPS), rather than transforming inorganic nitrogen in the dissimilation pathway. In addition, the proportion of unsaturated fatty acids was higher in strains cultured at low temperatures. At the molecular level, the adjustment of membrane transport, synthesis of cofactors and vitamins, and transcriptional regulators might contribute to the survival of the strain under cold conditions. Moreover, nucleotide precursor synthesis, translation, and oxidative and temperature stress response mechanisms also enhanced the resistance of strain H-b to low temperatures. The results suggest that combining multiple regulatory mechanisms and synergistic adaptation to cold stress enabled the growth and relatively high nitrogen removal rate (27.22%) of strain H-b at 5°C. By clarifying the mechanism of regulation and cold resistance of strain H-b, a theoretical foundation for enhancing the application potential of this functional bacterium for nitrogen-contaminated wastewater treatment was provided. IMPORTANCE The newly isolated aerobic denitrifying bacterium Bacillus simplex H-b removed various forms of inorganic nitrogen (nitrate, nitrite, and ammonium) from wastewater, even when the temperature was as low as 5°C. Although this environmentally functional bacterium has been suggested as a promising candidate for nitrogen-contaminated water treatment at low temperatures, understanding its cold adaptation mechanism during aerobic denitrification is limited. In this study, the cold tolerance mechanism of this strain was comprehensively explained. Furthermore, a theoretical basis for the practical application of this type of functional bacterium for nitrogen removal in cold regions is provided. The study expands our understanding of the survival strategy of psychrophilic bacteria and hence supports their further utilization in wastewater treatment applications.

Heterotrophic nitrification and aerobic denitrification characteristics of the psychrotolerant Pseudomonas peli NR-5 at low temperatures

The nitrogen removal efficiency of heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria can be seriously inhibited at low temperatures (< 15 °C). A novel psychrotolerant bacterium, Pseudomonas peli NR-5 (P. peli NR-5), with efficient HN-AD capability was isolated and screened from river sediments in cold areas. When P. peli NR-5 was aerobically cultivated for 60 h at 10 °C with NH₄⁺-N, NO₃^--N, and NO₂^--N as the sole nitrogen sources (N 105 mg/L), the nitrogen removal efficiencies were 97.3, 95.3, and 87.8%, respectively, without nitrite accumulation, and the corresponding average nitrogen removal rates were 1.71, 1.67, and 1.55 mg/L/h, respectively. Meanwhile, P. peli NR-5 exhibited excellent simultaneous nitrification and denitrification capabilities at 10 °C. Sodium succinate was the most favorable carbon substrate for bacterial growth and ammonia removal by strain NR-5. The optimal culture conditions determined by the response surface methodology model were a carbon to nitrogen ratio of 5.9, temperature of 11.5 °C, pH of 7.0, and shaking speed of 144 rpm. Under these conditions, 99.1% of the total nitrogen was removed in the verification experiments, which was not significantly different from the predicted maximum removal in the model (99.6%). Six functional genes participating in the HN-AD process were successfully obtained by polymerase chain reaction amplification, which further confirmed the HN-AD capability of P. peli NR-5 and proposed the metabolic pathway of HN-AD. The above results provide a theoretical background of psychrotolerant HN-AD bacteria in wastewater purification under low-temperature conditions.

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.

Cooperation of heterotrophic bacteria enables stronger resilience of halophilic assimilation biosystem than nitrification system under long-term stagnation

Long-term stagnation of biosystems (with no or very little wastewater) owing to seasonal downtime or failure maintenance brings great challenges to the performance recovery after system restart. In particular, the reduction of microbial activity and change of dissolved organic matter (DOM) affect the effluent quality and subsequent treatment procedures. Monitoring the dynamics and resilience of biosystems after long-term stagnation is important to formulate targeted countermeasures for system stability. However, the influence of long-term stagnation on autotrophic nitrification (AN) and heterotrophic assimilation (HA) biosystems has not been systematically explored. Here, we used halophilic AN and HA systems to study the stability and resilience of two nitrogen removal consortia after long-term stagnation. The results showed that 97.5 % and 93 % of ammonium and 47.0 % and 90.1 % of total nitrogen were removed using the halophilic AN and HA systems, respectively, in the stable period. After four weeks of stagnation, the HA system showed stronger resilience than AN system, in terms of faster recovery of treatment performance, and less fluctuations in sludge settleability and extracellular polymeric substances. In addition, after the stagnation period, the DOM of AN system was rich in low-molecular refractory humic acid, whereas that of HA system was rich in high-molecular proteins. The stagnation period led to the replacement of the dominant heterotrophic functional microorganisms, Paracoccus and Halomonas, with Muricauda and Marinobacterium in the HA system. The microbial network results revealed that the cooperation of heterotrophic bacteria enables stronger resilience of the HA system from prolonged stagnation than the AN system. In addition, the nitrogen removal efficiency, protein to polysaccharide ratio of EPS and fluorescence intensity of DOM were significantly correlated with the microbial community composition. These results suggest that AN system has greater risks in terms of treatment performance and sludge stability than the system after long-term stagnation.

Nitrogen removal and mechanism of an extremely high-ammonia tolerant heterotrophic nitrification-aerobic denitrification bacterium Alcaligenes faecalis TF-1

A novel heterotrophic nitrifying bacterium with high salt and high ammonia nitrogen tolerance, Alcaligenes faecalis TF-1, was isolated from the leachate of a landfill. The verification of nitrogen removal efficiency of different nitrogen sources and PCR amplification electrophoresis results showed that the HN-AD pathway of the strain TF-1 was NH₄⁺ → NH₂OH → NO → N₂O → N₂. The results of parameter optimization showed that the optimal nitrogen removal conditions were as follows: sodium citrate as carbon source, C/N = 16, pH = 7, and NH₄⁺-N loading of 808.21 mg/L. The strain TF-1 could remove about 94.60% of ammonia nitrogen (1963.94 mg/L). The salinity tolerance range of the strain TF-1 was 0-70 g/L, and the removal efficiency was 52.87% at salinity 70 g/L and NH₄⁺-N concentration 919.20 mg/L and 55.67% at pH = 10 and NH₄⁺-N concentration 994.82 mg/L. The extreme environmental adaptability and remarkable nitrogen removal performance make this strain a promising candidate in leachate treatment.

Simultaneous removal of high concentrations of ammonia nitrogen and calcium by the novel strain Paracoccus denitrificans AC-3 with good environmental adaptability

The novel Paracoccus denitrificans AC-3 strain was isolated and displayed outstanding purification capability for high concentrations of ammonia nitrogen (NH₄⁺-N) and calcium (Ca²⁺). Meanwhile, the strain exhibited excellent environmental adaptability within a wide pH range and high levels of NH₄⁺-N and Ca²⁺. Nitrogen balance analysis demonstrated that the pathways of NH₄⁺-N removal consisted of 80.12% assimilation and 16.60% heterotrophic nitrification aerobic denitrification (HNAD). In addition, Ca²⁺ was removed by forming calcium carbonate (CaCO₃) with carbonate (CO₃^2-) and bicarbonate (HCO₃^-). CO₃^2-and HCO₃^- were obtained from carbon dioxide (CO₂) hydration, which was catalyzed by carbonic anhydrase (CA) secreted by strain AC-3. The alkaline environment for carbonate precipitation was provided by CA and HNAD. The resulting CaCO₃ existed in the form of calcite and exhibited a unique morphology and elemental composition.

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.

Diverse nirS-type Denitrifying Bacteria Contribute to Vital Nitrogen Loss in Natural Acidic Red Soils

Denitrifying bacteria, playing a key role in nitrogen removal in ecosystem, are highly diverse and complex in their community composition. However, there were few reports on the abundance, community composition, and the contribution to nitrogen loss of denitrifiers in natural acidic red soils. In this study, we investigated the structure and function of nirS-type denitrifying bacteria in ten natural red soil samples collected from nine provinces in southern China, based on quantitative polymerase chain reaction (qPCR) and high-throughput sequencing techniques. Nitrogen loss from microbial denitrification in red soils of southern China was estimated up to 9.86 Tg N per year based on ¹⁵N isotope tracing method. The abundance of nirS-type denitrifiers varied from 8.41 × 10⁵ to 2.55 × 10⁹ copies per gram of dry weight. The community of nirS-type denitrifying bacterial was revealed, which contained 50 dominant OTUs assigned to 9 clusters phylogenetically related to Marinobacter, Rhodobacter, and other uncultured species. pH was the key factor affecting both denitrification rates and community composition. Our results demonstrate that nirS-type denitrifying bacteria have higher abundance, diversity, and contribution to the nitrogen loss in natural acidic red soils of southern China.

Membrane penetration of nitrogen and its effects on nitrogen removal in dual-chambered microbial fuel cells

Owing to membrane penetration, a novel route of nitrogen removal was proposed in a dual-chamber microbial fuel cell with a proton exchange membrane (PEM). The results showed that NH₄⁺-N rapidly migrated across PEM with a mass transfer coefficient (K_A) of 1.79 ± 0.51 × 10^-4 cm s^-1, 50% of which was oxidized to NO₃^--N in the cathode chamber, then the remainder being eliminated by short-cut nitrification/denitrification. Meanwhile, NO₃^--N went across the PEM again with a low K_A of 5.50 ± 0.24 × 10^-6 cm s^-1, and was subsequently reduced via anodic denitrification. In the anode, the functional microorganisms were divided into exoelectrogenic bacteria (46.2%) and denitrifying bacteria (37.3%), while the dominated bacteria were mainly affiliated with nitrifying bacteria (19.6%) and aerobic denitrifying bacteria (52.9%) in the cathode. These findings provide a new insight into nitrogen removal during bioelectrochemical treatment of actual wastewater.

Ammonium and hydroxylamine can be preferentially removed during simultaneous nitrification and denitrification by Pseudomonas taiwanensis EN-F2

To overcome a large amount of nitrite accumulation and poor removal rate for hydroxylamine, a simultaneous nitrification and denitrification (SND) bacterium was isolated and identified as Pseudomonas taiwanensis EN-F2 by DNA sequencing. Strain EN-F2 could remove 100% of ammonium (52.90 mg/L), 100% of hydroxylamine (23.32 mg/L), 86.99% of nitrite (56.32 mg/L) and 89.21% of nitrate (56.18 mg/L) with a maximum removal rate of 8.72, 2.12, 4.55 and 5.80 mg/L/h, respectively. Ammonium and hydroxylamine could be preferentially removed during the SND process. The nitrite removal rate and cell growth were substantially enhanced by 2.10 mg/L/h and 0.45 after supplementation of hydroxylamine. The specific activities of ammonia monooxygenase (AMO), hydroxylamine oxidoreductase (HAO), nitrate reductase (NR), nitrite reductase (NIR) were successfully detected as 0.95, 0.31, 0.42 and 0.03 U/mg protein, respectively. All results demonstrated that strain EN-F2 could perform SND to remove multiple nitrogen sources from wastewater.

Effects of different carbon sources on the removal of ciprofloxacin and pollutants by activated sludge: Mechanism and biodegradation

This research investigated the effects of ciprofloxacin (CIP) (0.5, 5, and 20 mg/L) on SBR systems under different carbon source conditions. Microbial community abundance and structure were determined by quantitative PCR and high-throughput sequencing, respectively. The biodegradation production of CIP and possible degradation mechanism were also studied. Results showed that CIP had adverse effects on the nutrient removal from wastewater. Compared with sodium acetate, glucose could be more effectively used by microorganisms, thus eliminating the negative effects of CIP. Glucose stimulated the microbial abundance and increased the removal rate of CIP by 18%-24%. The mechanism research indicated that Proteobacteria and Acidobacteria had a high tolerance for CIP. With sodium acetate as a carbon source, the abundance of nitrite-oxidizing bacterial communities decreased under CIP, resulting in the accumulation of nitrite and nitrate. Rhodanobacter and Microbacterium played a major role in nitrification and denitrification when using sodium acetate and glucose as carbon sources. Dyella and Microbacterium played positive roles in the degradation process of CIP and eliminated the negative effect of CIP on SBR, which was consistent with the improved removal efficiency of pollutants.

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.

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.

Characterization of Oral Bacterial Composition of Adult Smokeless Tobacco Users from Healthy Indians Using 16S rDNA Analysis

The present investigation is aiming to report the oral bacterial composition of smokeless tobacco (SLT) users and to determine the influence of SLT products on the healthy Indian population. With the aid of the V3 hypervariable region of the 16S rRNA gene, a total of 8,080,889 high-quality reads were clustered into 15 phyla and 180 genera in the oral cavity of the SLT users. Comparative analysis revealed a more diverse microbiome where two phyla and sixteen genera were significantly different among the SLT users as compared to the control group (p-value < 0.05). The prevalence of Fusobacteria-, Porphyromonas-, Desulfobulbus-, Enterococcus-, and Parvimonas-like genera among SLT users indicates altered bacterial communities among SLT users. Besides, the depletion of health-compatible bacteria such as Lactobacillus and Haemophilus also suggests poor oral health. Here, the majority of the altered genera belong to Gram-negative anaerobes that have been reported for assisting biofilm formation that leads in the progression of several oral diseases. The PICRUSt analysis further supports the hypothesis where a significant increase in the count of the genes involved in the metabolism of nitrogen, amino acids, and nicotinate/nicotinamide was observed among tobacco chewers. Moreover, this study has a high significance in Indian prospects where the SLT consumers are prevalent but we are deficient in information on their oral microbiome.

Application of glucose for improving NH4+-N removal in micro-polluted source water by immobilized heterotrophic nitrifiers at low temperature

Bio-enhanced activated carbon (BEAC) filters have shown potential in source water purification. The key drawback of this system is the difficulty of the set-up at low temperature. Here, glucose was applied to help immobilize more functional heterotrophic nitrifiers and further improve NH₄⁺-N removal by BEAC. Results showed that pre-loading glucose on granular activated carbon could achieve better immobilization efficiency with 5.12 × 10⁸ CFU/g-DW C biomass and 3.77 mg TF/L/g-DW C dehydrogenase activity after artificial immobilization, which were separately 12.5 and 4.2 times of the control. 95-d running data at different conditions showed the superiority of both immobilization and NH₄⁺-N removal could last and defend environment changes during relatively long period. Even at the end of operating, the abundance of targeting genus (Acinetobacter) still occupied 9.59% of microbial communities on BEAC, while this value was only 1.24% without pre-loading glucose. Biolog-ECO plate analysis found pre-loading glucose improved organic nitrogen metabolism effectively, along with carbohydrate, amino, alcohol, amine and carboxylic acid metabolism on BEAC.

Identification of optimal parameters for treatment of high-strength ammonium leachate by mixed communities of heterotrophic nitrifying/aerobic denitrifying bacteria

Heterotrophic nitrifying and aerobic denitrifying bacteria (HNADB) are important for partial nitrification treatment of high strength ammonium leachate. However, conditions for their optimal performance in mixed reactor systems have yet to be determined. In this study, optimal parameters were identified and included free ammonia (FA) concentrations below 40 mg/L, a dissolved oxygen concentration of 1.2 mg/L, a carbon to nitrogen ratio of 5 and a reflux ratio of 4. These conditions were applied to a continuous anoxic/oxic membrane moving biofilm reactor treating raw incineration leachate with high total ammonium nitrogen (TAN = 1400 mg/L). Ammonium conversion and nitrogen removal efficiencies of 99% and 86% were achieved. Autotrophic ammonia oxidizing bacteria were inhibited at FA concentrations above 25 mg/L. HNADB, particularly Paracoccus species, contributed to ammonium conversion at high FA (25-40 mg/L). These results show that leachate with high TAN and FA can be treated using parameters that support the growth of HNADB.

Performance and microbial community analysis of a bio-contact oxidation reactor during the treatment of low-COD and high-salinity oilfield produced water

The multistage bio-contact oxidation reactor (BCOR) is a widely used biological strategy to treat wastewater, however, little is known about the performance and microbial community information of BCOR during the treatment of low-COD and high-salinity oilfield produced water. In this study, the performance of a multistage BCOR in treating produced water was investigated. The result suggested the BCOR could efficiently remove COD, BOD₅, NH₄⁺-N, and oil pollutants. Besides, high-throughput sequencing analysis revealed that oil content was the main variable in shaping the community structure. The highest total relative abundance of potential pollutants degraders in first BCOR stage suggested significant role of this stage in pollutants removal. In addition, the correlation analysis disclosed the key functional genera during the degradation process, including Rhodobacter, Citreibacter, and Roseovarius. Moreover, network analysis revealed that the microbial taxa within same module had strong ecological linkages and specific functions.

A novel halophilic Exiguobacterium mexicanum strain removes nitrogen from saline wastewater via heterotrophic nitrification and aerobic denitrification

The utilization of halophilic bioresources is limited due to a lack of isolation and characterization work. A halophilic bacterium strain SND-01 of Exiguobacterium mexicanum was isolated in this study, which is the first report on its novel function in heterotrophic nitrification-aerobic denitrification (HN-AD). The strain SND-01 is slightly halophilic, surviving at 0 up to 9% (w/v) salinity. When utilizing ammonium, nitrate or nitrite as the sole nitrogen source in aerobic conditions, the isolated strain showed the maximum nitrogen removal rate of 2.24 ± 0.14 mg/(L·h), 3.63 ± 0.21 mg/(L·h) and 2.30 ± 0.23 mg/(L·h), respectively. Functional genes and key enzymes involved in heterotrophic-aerobic nitrogen transformations were characterized, establishing the pathway of HN-AD. The nitrogen removal via HN-AD is dependent on the C/N ratio, salinity and temperature. The halophilic Exiguobacterium mexicanum strain SND-01 shows a significant potential in biotreatment of saline wastewater in an easy and cost-effective way.

Nitrate removal from low C/N wastewater at low temperature by immobilized Pseudomonas sp. Y39-6 with versatile nitrate metabolism pathways

For solving the challenge in nitrate removal from low C/N wastewater at low temperature, Pseudomonas sp. Y39-6 was isolated and used in nitrate removal. It showed aerobic-heterotrophic denitrification with rate of 1.77 ± 0.31 mg/L·h and unusual aerobic-autotrophic nitrate removal (rate of 0.324 mg/L·h). The aerobic-autotrophic nitrate removal mechanisms were deep investigated by analyzing the nitrate removal process and genomic information. At aerobic-autotrophic condition, the strain Y39-6 could assimilate nitrate to amino acid (NO₃^- + PHA + CO₂ → C₅H₇O₂N) with the carbon source from Polyhydroxyalkanoic acid (PHA) degradation and CO₂ fixation. Flagella motivation, swarming activity and extracellular polymeric substances (EPS) production regulated Pseudomonas sp. Y39-6 forming biofilm. Carriers immobilized with Pseudomonas sp. Y39-6 were used in moving bed biofilm reactor (MBBR) and achieved 24.83% nitrate removal at C/N < 1 and 4 °C. Results of this study provided a practical way for nitrogen removal from low C/N wastewater in cold region.

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

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

A coupled UV photolysis-biodegradation process for the treatment of decabrominated diphenyl ethers in an aerobic novel bioslurry reactor

The commercial flame retardant is an emerging contaminant (EC) commonly found in soils and sediments. A coupled UV-photolysis-biodegradation process was used to decompose decabromodiphenyl ether (BDE-209) in clay slurries. A novel bioslurry bioreactor (NBB) was employed in which BDE-209 degradation was maximized by the simultaneous application of LED UVA irradiation and biodegradation by a mixed bacterial culture. The rate of BDE-209 degradation decreased in the order: coupled UV photolysis-biodegradation (1.31 × 10-2 day-1) > UV photolysis alone (1.10 × 10-2 day-1) > biodegradation alone (1.00 × 10-2 day-1). Degradation intermediates detected included hydroxylated polybrominated diphenylethers, partially debrominated PBDE congeners and polybrominated dibenzofuran. The UV-resistant bacterial strains isolated that could utilize BDE-209 as a sole carbon source included Stenotrophomonas sp., Pseudomonas sp., and Microbacterium sp. These strains encoded important functional genes such as dioxygenase and reductive dehalogenases. Continuous UV irradiation during the NBB process affected various biochemical oxidative reactions during PBDEs biodegradation. Simultaneous photolysis and biodegradation in the NBB system described reduces operational time, energy, expense, and maintenance-demands required for the remediation of BDE-209 when compared to sequential UV-biodegradation process or to biodegradation alone.

Synthesized akhtenskites remove ammonium and manganese from aqueous solution: removal mechanism and the effect of structural cations

Ammonium and manganese removal by tunnel-structured manganese oxide is still enigmatic. Herein, tunnel-structured akhtenskites with different structural cations (Na–MnO_x, Mg–MnO_x Ca–MnO_x, Fe–MnO_x) were synthesized by the KMnO₄ and Mn²⁺ reaction in the presence of different metal cations, and were used to remove ammonium and manganese from aqueous solution. The results of the batch adsorption experiments indicated that akhtenskites effectively removed NH₄⁺ and Mn²⁺, and the removal process fitted the pseudo-second-order model. By measuring the concentration of nitrate and nitrite, discriminating the adsorbed and oxidized Mn²⁺, and testing the zeta potential of the oxides, it can be concluded that NH₄⁺ was merely removed by electrostatic adsorption via Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Mn–O⁻; Mn²⁺ could also be adsorbed by ion exchange with Mn–OH, and the adsorbed Mn²⁺ could be partly oxidized. The structural properties of the akhtenskites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) specific area, and X-ray photoelectron spectroscopy (XPS). The experimental results showed that ions with higher valence can result in a higher percentage of Mn(iii) in akhtenskite. Mg²⁺ can result in a lower proportion of lattice oxygen in the oxide, and Fe³⁺ can increase the pH of the point of zero charge. Both of them were unfavored for the oxidation of Mn²⁺. Moreover, it was found that Ca–MnO_x had optimal removal performance in the catalytic oxidation of Mn²⁺ owing to appropriate percentages of O_latt and Mn(iii) and lower zeta potential. This study provides new insights into the synthesis and application of manganese oxides.

Akhtenskites merely remove NH₄⁺ by adsorption, but remove Mn²⁺ by adsorption and catalytic oxidation simultaneously. The removal efficiency and crystal structure are obviously affected by the structure cations.

A study on the nitrogen removal efficacy of bacterium Acinetobacter tandoii MZ-5 from a contaminated river of Shenzhen, Guangdong Province, China

Heterotrophic nitrification-aerobic denitrification (HN-AD) has advantages over the traditional nitrogen removal process when removing multiple types of nitrogen in wastewater treatment. Acinetobacter tandoii MZ-5, which is capable of HN-AD, was isolated from the sediment of a polluted river for the first time. It used NH₄⁺-N, NO₂^--N and NO₃^--N as sole nitrogen sources with maximum removal rates of 2.28, 1.18 and 1.04 mg L^-1h^-1, respectively. Simultaneous nitrification and denitrification were observed when using mixed N sources and NH₄⁺-N was preferentially utilized. High nitrogen removal efficiencies (>90%) were achieved under the following conditions: C/N ratio 11-18, pH 6-8, 25-30 °C and dissolved oxygen 7.35-7.66 mg L^-1. Strain MZ-5 was effective at treating wastewater from landfill leachate treatment plants, with NH₄⁺-N, NO₃^--N and total nitrogen (TN) removal efficiencies of 99.28%, 44.85% and 45.31%, respectively. Thus, strain MZ-5 may be a good candidate for wastewater treatment.

Applying constructed wetland-microbial electrochemical system to enhance NH4+ removal at low temperature

NH₄⁺ removal at low temperature (<10 °C) has baffled researchers and engineers for decades. Bioelectrochemical process has been increasingly valued as a promising approach to enhance NH₄⁺ removal by both electrochemical and stimulated microbial processes. The feasibility and the mechanism of enhanced NH₄⁺ removal were investigated in Constructed Wetland-Microbial Electrochemical System (CW-MES) with different electrode spacings including Constructed Wetland-Microbial Fuel Cell (CW-MFC) and Constructed Wetland-Microbial Electrolysis Cell (CW-MEC) at low temperature. Solar cell panel was firstly implemented in CW-MEC to enhance NH₄⁺ removal. The low-temperature operation lasted for about four months, CW-MEC successfully enhanced NH₄⁺ removal while CW-MFC did not exhibit positive effect. The NH₄⁺-N removal efficiency of CW-MEC achieved 88.2 ± 7.0%, which was 11.7 ± 6.5% higher than conventional constructed wetland (CCW). The maximum NH₄⁺-N removal efficiency of CW-MEC achieved 100%. The average NH₄⁺-N mass removal rate was 436.02 mg m^-2 d^-1. It was found that NH₄⁺ was mainly removed by the nitrification-autotrophic denitrification process in CW-MES while it was mainly converted to NO₃^- in CCW. Ammoxidation and denitrification were both enhanced by electricity while NH₄⁺ was used as the main substrate for electricity generation. AOA (Candidatus Nitrosocosmicus) and NOB (Nitrospira) were the main contributors to nitrification. This study provided a cost-effective and sustainable method for electrochemically enhanced microbial NH₄⁺ removal at low-temperature and revealed the relevant mechanism.

Bifunctional cathode using a biofilm and Pt/C catalyst for simultaneous electricity generation and nitrification in microbial fuel cells

Biofouling frequently causes catalyst deterioration at the cathode of microbial fuel cells (MFCs). A biofilm-covered Pt/C cathode (BPC) was fabricated via in situ cultivation of a biofilm on a Pt/C cathode (PC) in a dual-chambered MFC, which enables effective removal of NH4+-N and copious generation of electricity. Experimental results show 99% NH4+-N removal by the nitrifying bacteria that constitute 35.7% of all microorganisms on the BPC and a maximum BPC-MFC power density of 0.97 W/m2, which is comparable to that of PC-MFCs (0.99 W/m2). BPC biofilm size is restricted by the limited amount of organic material in the cathode chamber, which constrains the biomass to less than 0.3 g protein /m2. The bifunctional-cathode equipped MFC shows great promise as an energy-saving technology for wastewater treatment in the future.

Influences of organic nitrogen on the removal of inorganic nitrogen from complicated marine aquaculture water by Marichromatium gracile YL28

The sediment-water interface is not only an important location for substrate conversion in a mariculture system, but also a major source of eutrophication. This study aimed to clarify the characteristics of inorganic nitrogen (ammonia, nitrite and nitrate) removal by Marichromatium gracile YL28 in the presence of both organic nitrogen and inorganic nitrogen. The results showed that, in the presence of peptone or urea, seaweed oligosaccharides (SOS) effectively enhanced the ammonia removal capacity of YL28 (6.42 mmol/L) and decreased the residual rate by 54.04% or 8.17%, respectively. With increasing peptone or urea concentrations, the removal of both ammonia and nitrate was gradually inhibited, and the residual rates of ammonia and nitrate reached 22.56-34.36% and 12.03-15.64% in the peptone system and 20.65-24.03% and 12.20-13.21% in the urea system, respectively. However, in the control group the residual rates of ammonia and nitrate reached 11.97% and 5.12%, respectively. In addition, the concentrations of peptone and urea did not affect nitrite removal, and YL28 displayed better cell growth and nitrogen removal activity in the presence of bait and SOS. Overall, the ability of YL28 to remove inorganic nitrogen was enhanced in the presence of organic nitrogen.

Heterotrophic nitrification and aerobic denitrification by a novel Acinetobacter sp. ND7 isolated from municipal activated sludge

A novel strain was isolated from municipal activated sludge and identified as Acinetobacter sp. ND7 based on its phenotypic and phylogenetic characteristics, which had efficient capability for heterotrophic nitrification and aerobic denitrification. Strain ND7 could remove approximately 99.8% of ammonium-N (51.0 mg/L), 96.2% of nitrite-N (51.8 mg/L) and 97.18% of nitrate-N (52.1 mg/L), with the maximum specific removal rate of 5.74, 4.17 and 3.63 mg/(L h), respectively. Ammonium was manifested to be utilized preferentially during simultaneous nitrification and denitrification. The functional genes hao, napA and nirS were successfully amplified by PCR, further evidencing the heterotrophic nitrification and aerobic denitrification capability of Acinetobacter sp. ND7. The optimal conditions for nitrogen removal were temperature of 35 °C, C/N ratio of 8. Acinetobacter sp. ND7 displays superior performance for nitrogen removal, with no nitrite accumulation under aerobic condition, and thus has significant potential for practical application for nitrogen removal from wastewater.

Effect of iron and manganese on ammonium removal from micro-polluted source water by immobilized HITLi7T at 2 °C

In this study, trace metals (Fe & Mn) were applied to enhance NH₄⁺-N removal in source water at 2 °C, and 22.7% of initial 2.20 mg/L NH₄⁺-N was removed by pre-treating granular activated carbon (GAC) with Fe & Mn before immobilizing Acinetobacter harbinensis HITLi7^T to form biological activated carbon (BAC). Biomass and dehydrogenase activity (DHA) on this modified BAC were 2.80 × 10⁸ CFU/g-DW C and 0.50 mg/L/g-DW C, respectively, both the highest. Additionally, 4.76 times more biomass and 9.76 times higher DHA of HITLi7^T were observed in the cultivation with Fe & Mn dosing. Extracellular polymeric substances (EPS) measurements found Fe & Mn dosing could increase total EPS amount (44.3% higher) and polysaccharide (PS) ratio (1.50% higher) secreted by HITLi7^T. According to the results of 3D-excitation-emission matrix (3D-EEM) fluorescence spectra and infrared spectra (FTIR) analysis, Fe and Mn promoted the secretion of tryptophan-like substances and changed functional groups COH, COC, CO and COOH, which are associated with protein and PS.

Preparation, characterization, and application of macroporous activated carbon (MAC) suitable for the BAC water treatment process

To address the sharp decrease in efficiency of the biological activated carbon (BAC) process at low temperatures, a new type of activated carbon (AC), macroporous activated carbon (MAC), was developed from bamboo waste scraps via a special compression, carbonation and activation process without the introduction of chemicals. MAC contains not only the micron-level macropores (V_maco > 0.71 ml/g) sufficient for bacteria to access and multiply, but ensures the developed smaller pores (particularly micropores, V_micro > 0.41 ml/g) and a higher hardness (>90%). In addition, the desired volume of macropores with an adiabatic function, which will provide livable space environment for bacteria, can be obtained by adjusting the compression ratio (1:5-1:10). Because of the maximum macropore volume (V_maco = 0.805 ml/g) and the most abundant macropore distribution (particularly diameters>10,000 nm), MAC (1:6) was selected for the parallel experiment in the laboratory, taking three representative commercial ACs (PICABIOL® 2, raw coal AC-1 and briquetting AC-2) as controls, in which the filtration effluent of a water treatment plant was used as the influent and glucose was added to accelerate bacterial growth. The results showed that MAC (1:6) exhibited the highest DOC removal and biological activity at room/low temperatures (4 °C), indicating that the abundant macropores distribution with adiabatic function in MAC (1:6) is conducive to the growth and breeding of microorganisms. It is equivalent to artificially increasing the surface suitable for bacteria attachment. This is coupled with the higher adsorption capacity for pollutants supplied by the developed micropores in MAC, which provided the substrate for bacteria growth, thus forming a benign circle for water treatment by the BAC process. The results provide significant technical support for BAC's application, particularly at cold temperatures.

High-efficiency inorganic nitrogen removal by newly isolated Pannonibacter phragmitetus B1

An aerobic heterotrophic nitrogen removal bacterium strain, B1, was isolated from aquaculture water and identified as Pannonibacter phragmitetus (99% similarity) by 16S rRNA sequencing analysis. When ammonium, nitrite or nitrate was the sole nitrogen source, with an initial nitrogen concentration of 14 mg/L, the nitrogen removal efficiencies were 98.66%, 99.96% and 98.73%, respectively, and the corresponding maximum removal rates reached as high as 1.16, 0.77 and 0.81 mg/L/h, respectively. In the presence of NH₄⁺-N, the removal efficiency of 56 mg/L NO₂^--N within 27 h increased by 83.50%, and the corresponding removal rate reached as high as 1.72 mg/L/h. Additionally, different carbon sources (dl-malic acid, sucrose, sodium citrate, and glucose) could be utilized in nitrogen removal. Sequence amplification indicates that the denitrification genes nirK, norB and narG are present in strain B1. All results demonstrate that strain B1 has high promise for future applications of removing inorganic nitrogen from wastewater.

Research on the enhancement of biological nitrogen removal at low temperatures from ammonium-rich wastewater by the bio-electrocoagulation technology in lab-scale systems, pilot-scale systems and a full-scale industrial wastewater treatment plant

In cold areas, nitrogen removal performance of wastewater treatment plants (WWTP) declines greatly in winter. This paper systematically describes the enhancement effect of a periodic reverse electrocoagulation technology on biological nitrogen removal at low temperatures. The study showed that in the lab-scale systems, the electrocoagulation technology improved the biomass amount, enzyme activity and the amount of nitrogen removal bacteria (Nitrosomonas, Nitrobacter, Paracoccus, Thauera and Enterobacter). This enhanced nitrification and denitrification of activated sludge at low temperatures. In the pilot-scale systems, the electrocoagulation technology increased the relative abundance of cold-adapted microorganisms (Luteimonas and Trueperaceae) at low temperatures. In a full-scale industrial WWTP, comparison of data from winter 2015 and winter 2016 showed that effluent chemical oxygen demand (COD), NH₄⁺-N, and NO₃^--N reduced by 10.37, 3.84, and 136.43 t, respectively, throughout the winter, after installation of electrocoagulation devices. These results suggest that the electrocoagulation technology is able to improve the performance of activated sludge under low-temperature conditions. This technology provides a new way for upgrading of the performance of WWTPs in cold areas.

Substrates removal and growth kinetic characteristics of a heterotrophic nitrifying-aerobic denitrifying bacterium, Acinetobacter harbinensis HITLi7T at 2 °C

In order to investigate the heterotrophic nitrification and aerobic denitrification ability of Acinetobacter harbinensis HITLi7^T at 2 °C, both the growth parameters and substrates utilization characteristics were tested and appropriated kinetic models were obtained in this study. Under the initial concentration of 5 mg/L, the maximum NH₄⁺-N and NO₃^--N degradation rates were 0.076 mg NH₄⁺-N/L/h and 0.029 mg NO₃^--N/L/h, respectively. At the simultaneous presence of 2.5 mg/L NH₄⁺-N and NO₃^--N, the maximum nitrate removal rate increased to 0.054 mg NO₃^--N/L/h (1.86 folds), while a slight decrease was observed in NH₄⁺-N removal. Two double-substrate models, Contois-Contois (1) for NH₄⁺-N and TOC, Monod-Contois (2) for NO₃^--N and TOC matched well with the experimental data. The kinetic parameters were determined as μ_max1 = 0.095 h^-1, B_A1 = 0.012 mg/L, B_T1 = 0.784 g TOC/g biomass (R₁² = 0.9997), and μ_max2 = 0.032 h^-1, K_N2 = 0.375 mg/L, B_T2 = 1.108 g TOC/g biomass (R₂² = 0.9731) by multiple regression equation.

Highly efficient nitrogen removal of a coldness-resistant and low nutrient needed bacterium, Janthinobacterium sp. M-11

A novel heterotrophic nitrification-aerobic denitrification bacterium, identified as Janthinobacterium sp. M-11, was isolated from the Songhua River. When the initial ammonium concentration was 5 mg·L^-1, 98% of ammonium was removed under cold condition (2 °C) with the C/N ratio of 5 at initial pH 7 and aerobic condition, which demonstrated the significant ammonium removal capacity of M-11 with low nutrient consumption at cold temperature. Denitrification processes under aerobic and anaerobic conditions were also investigated. 89% of nitrite and 89% of nitrate were removed under aerobic condition. Under anaerobic condition, 93% of nitrite and 98% of nitrate were removed. Interestingly, a high amount of nitrite accumulation was observed in the mid-stage of anaerobic denitrification for nitrate. This special phenomenon was probably because of the existence of narG gene amplified in the strain M-11, which would encode membrane-bound nitrate reductase and accelerate the nitrate conversion rate of M-11 under anaerobic condition.

Removal of Nitrate in Simulated Water at Low Temperature by a Novel Psychrotrophic and Aerobic Bacterium, Pseudomonas taiwanensis Strain J

Low temperatures and high pH generally inhibit the biodenitrification. Thus, it is important to explore the psychrotrophic and alkali-resisting microorganism for degradation of nitrogen. This research was mainly focused on the identification of a psychrotrophic strain and preliminary explored its denitrification characteristics. The new strain J was isolated using the bromothymol blue solid medium and identified as Pseudomonas taiwanensis on the basis of morphology and phospholipid fatty acid as well as 16S rRNA gene sequence analyses, which is further testified to work efficiently for removing nitrate from wastewater at low temperature circumstances. This is the first report that Pseudomonas taiwanensis possessed excellent tolerance to low temperature, with 15°C as its optimum and 5°C as viable. The Pseudomonas taiwanensis showed unusual ability of aerobic denitrification with the nitrate removal efficiencies of 100% at 15°C and 51.61% at 5°C. Single factor experiments showed that the optimal conditions for denitrification were glucose as carbon source, 15°C, shaking speed 150 r/min, C/N 15, pH ≥ 7, and incubation quantity 2.0 × 10⁶ CFU/mL. The nitrate and total nitrogen removal efficiencies were up to 100% and 93.79% at 15°C when glucose is served as carbon source. These results suggested that strain J had aerobic denitrification ability, as well as the notable ability to tolerate the low temperature and high pH.

A comparison study of the start-up of a MnOx filter for catalytic oxidative removal of ammonium from groundwater and surface water

As an efficient method for ammonium (NH₄⁺) removal, contact catalytic oxidation technology has drawn much attention recently, due to its good low temperature resistance and short start-up period. Two identical filters were employed to compare the process for ammonium removal during the start-up period for ammonium removal in groundwater (Filter-N) and surface water (Filter-S) treatment. Two types of source water (groundwater and surface water) were used as the feed waters for the filtration trials. Although the same initiating method was used, Filter-N exhibited much better ammonium removal performance than Filter-S. The differences in catalytic activity among these two filters were probed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and compositional analysis. XRD results indicated that different manganese oxide species were formed in Filter-N and Filter-S. Furthermore, the Mn3p XPS spectra taken on the surface of the filter films revealed that the average manganese valence of the inactive manganese oxide film collected from Filter-S (FS-MnO_x) was higher than in the film collected from Filter-N (FN-MnO_x). Mn(IV) was identified as the predominant oxidation state in FS-MnO_x and Mn(III) was identified as the predominant oxidation state in FN-MnO_x. The results of compositional analyses suggested that polyaluminum ferric chloride (PAFC) used during the surface water treatment was an important factor in the mineralogy and reactivity of MnO_x. This study provides the theoretical basis for promoting the wide application of the technology and has great practical significance.

Bacterial diversity and population shifts driven by spotlight wastewater micropollutants in low-temperature highly nitrifying activated sludge

In this study the influence of low-temperature (8°C), sludge retention time (SRT) and loading of spotlight wastewater micropollutants (MPs) on bacterial community of activated sludge was investigated with a special focus on nitrification. Two Sequencing batch reactors (SBR) and two membrane bioreactors (MBR) were operated with synthetic municipal-like wastewater receiving and not receiving ibuprofen, diclofenac, estrone and 17α-ethynylestradiol (EE2). Bacterial population studies were related to removal efficiencies of studied MPs. The results showed that studied bacterial communities significantly differed from all previously published nitrifying activated sludge communities. Exceptionally low concentration of autotrophic nitrifying bacteria were found (<0.5%) as well as no common heterotrophic nitrifies were presenting in activated sludge and therefore could not be related to the MPs removal. Additionally SRT had a spacious effect on the diversity of bacteria and bacterial population shifts under pressure of MPs. Growth of Firmicutes was suppressed by presence of MPs in all the reactors. Increase of MPs concentrations in wastewater improved the removal of EE2. Abundance of Delta- and Gammaproteobacteria showed positive correlation with diclofenac removal.