Effects of carbon sources and operation modes on the performances of aerobic denitrification process and its microbial community shifts

Efficient nitrogen removal by the aerobic denitrifying bacterium Pseudomonas stutzeri RAS-L11 under triple stresses of high alkalinity, high salinity, and tetracycline: From performance to mechanism

Efficient aerobic denitrification bacteria are rarely reported under triple stresses of high alkalinity, high salinity, and tetracycline. Here, strain Pseudomonas stutzeri RAS-L11 was isolated, under the optimal reaction conditions of C/N = 6, sodium acetate as carbon source, and pH 7.0-11.0. Moreover, RAS-L11 showed perfect nitrogen removal performance under dual and triple stresses. Specifically, the mean removal efficiency of total dissolved nitrogen for different medium (nitrate, nitrite, ammonia, nitrate and ammonia, and nitrite and ammonia) reached 92.35 %, 66.85 %, 71.33 %, 89.42 %, and 68.76 % under triple stresses. Nitrogen balance results indicated that biomass nitrogen accounted for a small percentage (4.48 % to 20.79 %). Furthermore, the nitrogen metabolism pathways and tetracycline, salinity, and alkaline tolerance-associated genes were also confirmed. Strain RAS-L11 achieved 42.67-70.72 % NO3--N and 83.72-88.53 % NH4+-N removal efficiencies in both sterilized and actual systems treating pharmaceutical wastewater. Our characterization of the RAS-L11 provides a reference for nitrogen removal of pharmaceutical wastewater.

Novel insights on ecological responses of short- and long-chain perfluorocarboxylic acids in constructed wetlands coupled with modified basalt fiber bio-nest

The first investigation based on constructed wetlands coupled with modified basalt fiber bio-nest (MBF-CWs) was performed under exposure of short- and long-chain perfluorocarboxylic acids (PFCAs). In general, both perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA) caused significant decline of chemical oxygen demand removal by 10.83 % and 4.73 %. However, only PFOA led to marked inhibition on total phosphorus removal by 12.51 % in whole duration. Suppression of removal performance resulted from side impacts on microbes by PFOA. For instance, activities of key enzymes like dehydrogenase (DHA), urease (URE), and phosphatase (PST) decreased by 52.77 %, 40.70 %, and 56.94 % in maximum under PFOA stress, while URE could alleviate over time. By contrast, distinct inhibition was only found on PST in later phases with PFBA exposure. PFCAs had adverse influence on alpha diversity of MBF-CWs, particularly long-chain PFOA. Both PFCAs caused enrichment of Proteobacteria, owing to increase of Gammaproteobacteria and Plasticicumulans by 22.04-35.79 % and 22.91-219.77 %. Nevertheless, some dominant phyla (like Bacteroidota and Acidobacteriota) and genera (like SC-I-84, Thauera, Subgroup_10, and Ellin6067) were only suppressed by PFOA, causing more hazards to microbial decontamination than PFBA did. As for plants, chlorophyll contents tend to decrease with PFOA treatment. Whereas, higher antioxidase activities and more lipid peroxidation products were uncovered in PFOA group, demonstrating more reactive oxygen species brought by long-chain PFCAs. This work offered new findings about ecological effects of MBF-CWs under PFCAs exposure, evaluating stability and sustainability of MBF-CW systems to treat sewage containing complex PFCAs.

Transition from sulfur autotrophic to mixotrophic denitrification: Performance with different carbon sources, microbial community and artificial neural network modeling

To address the limitations inherent in both sulfur autotrophic denitrification (SAD) and heterotrophic denitrification (HD) processes, this study introduces a novel approach. Three carbon sources (glucose, methanol, and sodium acetate) were fed into the SAD system to facilitate the transition towards mixotrophic denitrification. Batch experiments were conducted to explore the effects of influencing factors (pH, HRT) on the denitrification performance of the mixotrophic system. Carbon source dosages were varied at 12.5%, 25%, and 50% of the theoretical amounts required for HD (18, 36, and 72 mg/L, respectively). The results showed distinct optimal dosages for each of the three organic carbon sources. The mixotrophic system, initiated with sodium acetate at 25% of the theoretical value, demonstrated the highest denitrification performance, achieving NO3--N removal efficiency of 99.8% and the NRR of 6.25 mg/(L·h). In contrast, the corresponding systems utilizing glucose (at 25% of the theoretical value) and methanol (at 50% of the theoretical value) achieved lower removal efficiency of 77.0% and 88.4%, respectively. The corresponding NRRs were 4.85 mg/(L·h) and 5.65 mg/(L·h). Following the transition from SAD to a mixotrophic system, the abundance of Thiobacillus decreased from 78.5% to 34.4% at the genus level, and the mixotrophic system cultivated a variety of other denitrifying bacteria (Thauera, Aquimonas, Azoarcus, and Pseudomonas), indicating an enhanced microbial community structure diversity. The established artificial neural network (ANN) model accurately predicted the effluent quality of mixotrophic denitrification, which predicted values closely aligning with experimental results (R2 > 0.9). Furthermore, initial pH exerted greater relative importance for COD removal and sulfur conversion, while the relative importance of HRT was more pronounced for NO3--N removal.

Ultra-rapid development of 'solid' aerobic granular sludge by stable transition/filling of inoculated 'hollow' mycelial pellets in hypersaline wastewater

To overcome the long start-up period in cultivating aerobic granular sludge (AGS) under hypersaline environment, mycelial pellets (MPs) of halotolerant fungus Cladosporium tenuissimum NCSL-XY8 were inoculated to try to realize the ultra-rapid development of salt-tolerant AGS by stable transition of 'hollow' MPs into 'solid' AGS without apparent fragmentation. The granules directly met the standard of AGS after inoculating MPs (Day 0), and it basically satisfied relatively strict standards of AGS (SVI30 < 50 mL/g, D50 > 300 μm, D10 > 200 μm and SVI30/SVI5 > 0.9) under anaerobic/aerobic mode during whole cultivation processes. Microstructure of the granular cross section clarified that MPs with hollow/loose inner layer transitioned into solid/dense AGS under anaerobic/aerobic mode within 7 days, while formed skin-like floating pieces and unstable double-layer hollow granules under aerobic mode. Organics removal reached relatively stable within 13 days under anaerobic/aerobic mode, 6 days faster than aerobic mode. This study provided a strategy for ultra-rapid and stable development of AGS, which showed the shortest granulation period in various AGS-cultivation strategies.

Relating the carbon sources to denitrifying community in full-scale wastewater treatment plants

Carbon source is a key factor determining the denitrifying effectiveness and efficiency in wastewater treatment plants (WWTPs). Whereas, the relationships between diverse and distinct denitrifying communities and their favorable carbon sources in full-scale WWTPs were not well-understood. This study performed a systematic analysis of the relationships between the denitrifying community and carbon sources by using 15 organic compounds from four categories and activated sludge from 8 full-scale WWTPs. Results showed that, diverse denitrifying bacteria were detected with distinct relative abundances in 8 WWTPs, such as Haliangium (1.98-4.08%), Dechloromonas (2.00-3.01%), Thauera (0.16-1.06%), Zoogloea (0.09-0.43%), and Rhodoferax (0.002-0.104%). Overall, acetate resulted in the highest denitrifying activities (1.21-4.62 mg/L/h/gMLSS), followed by other organic acids (propionate, butyrate and lactate, etc.). Detectable dissimilatory nitrate reduction to ammonium (DNRA) was observed for all 15 carbon sources. Methanol and glycerol resulted in the highest DRNA. Acetate, butyrate, and lactate resulted in the lowest DNRA. Redundancy analysis and 16S cDNA amplicon sequencing suggested that carbon sources within the same category tended to correlate to similar denitrifiers. Methanol and ethanol were primarily correlated to Haliangium. Glycerol and amino acids (glutamate and aspartate) were correlated to Inhella and Sphaerotilus. Acetate, propionate, and butyrate were positively correlated to a wide range of denitrifiers, explaining the high efficiency of these carbon sources. Additionally, even within the same genus, different amplicon sequence variants (ASVs) performed distinctly in terms of carbon source preference and denitrifying capabilities. These findings are expected to benefit carbon source formulation and selection in WWTPs.

Exploratory study on the metabolic similarity of denitrifying carbon sources

Mixed carbon sources have been developed for denitrification to eliminate the "carbon dependency" problem of single carbon. The metabolic correlation between different carbon sources is significant as guidance for the development of novel mixed carbon sources. In this study, to explore the metabolic similarity of denitrifying carbon sources, we selected alcohols (methanol, ethanol, and glycerol) and saccharide carbon sources (glucose, sucrose, and starch). Batch denitrification experiments revealed that methanol-acclimated sludge improved the denitrification rate of both methanol (14.42 mg-N/gMLVSS*h) and ethanol (9.65 mg-N/gMLVSS*h), whereas ethanol-acclimated sludge improved the denitrification rate of both methanol (7.80 mg-N/gMLVSS*h) and ethanol (22.23 mg-N/gMLVSS*h). In addition, the glucose-acclimated sludge and sucrose-acclimated sludge possibly improved the denitrification rate of glucose and sucrose, and the glycerol-acclimated sludge improved the denitrification rate of volatile fatty acids (VFAs), alcohols, and saccharide carbon sources. Functional gene analysis revealed that methanol, ethanol, and glycerol exhibited active alcohol oxidation and glyoxylate metabolism, and glycerol, glucose, and sucrose exhibited active glycolysis metabolism. This indicated that the similarity in the denitrification metabolism of these carbon sources was based on functional gene similarity, and glycerol-acclimated sludge exhibited the most diverse metabolism, which ensured its good denitrification effect with other carbon sources.

A novel carbon emission evaluation model for anaerobic-anoxic-oxic urban sewage treatment

The proposal of the dual carbon goal and the blue economy in China has sparked a keen interest in carbon emissions reduction from sewage treatment. Carbon accounting in urban sewage plants serves as the foundation for carbon emission reduction in sewage treatment. This paper re-evaluated carbon accounting in the operational processes for urban sewage treatment plants to develop a novel carbon emission evaluation model for anaerobic-anoxic-oxic treatment plants. The results show that the carbon emissions generated by non-carbon dioxide gases far exceed the carbon emissions from carbon dioxide alone. Moreover, the recycling of sewage leads to carbon emissions reduction that offsets the carbon emissions generated during the operation of the sewage plant. Also, the carbon emissions generated by sewage treatment plants are lower than those generated by untreated sewage. The findings and insights provided in this paper provide valuable references for carbon accounting and the implementation of low-carbon practices in urban sewage treatment plants.

Mixotrophic denitrification process driven by lime sulfur and butanediol: Denitrification performance and metagenomic analysis

Heterotrophic sulfur-based autotrophic denitrification is a promising biological denitrification technology for low COD/TN (C/N) wastewater due to its high efficiency and low cost. Compared to the conventional autotrophic denitrification process driven by elemental sulfur, the presence of polysulfide in the system can promote high-speed nitrogen removal. However, autotrophic denitrification mediated by polysulfide has not been reported. This study investigated the denitrification performance and microbial metabolic mechanism of heterotrophic denitrification, sulfur-based autotrophic denitrification, and mixotrophic denitrification using lime sulfur and butanediol as electron donors. When the influent C/N was 1, the total nitrogen removal efficiency of the mixotrophic denitrification process was 1.67 and 1.14 times higher than that of the heterotrophic and sulfur-based autotrophic denitrification processes, respectively. Microbial community alpha diversity and principal component analysis indicated different electron donors lead to different evolutionary directions in microbial communities. Metagenomic analysis showed the enriched denitrifying bacteria (Thauera, Pseudomonas, and Pseudoxanthomonas), dissimilatory nitrate reduction to ammonia bacteria (Hydrogenophaga), and sulfur oxidizing bacteria (Thiobacillus) can stably support nitrate reduction. Analysis of metabolic pathways revealed that complete denitrification, dissimilatory nitrate reduction to ammonia, and sulfur disproportionation are the main pathways of the N and S cycle. This study demonstrates the feasibility of a mixotrophic denitrification process driven by a combination of lime sulfur and butanediol as a cost-effective solution for treating nitrogen pollution in low C/N wastewater and elucidates the N and S metabolic pathways involved.

Sodium hydroxide or tetramethylammonium hydroxide modified corncob combined with biodegradable polymers to prepare slow-release carbon source for wastewater denitrification

This study proposed a method to improve the bioavailability of artificially prepared carbon sources for the purpose of wastewater denitrification. This carbon source (named SPC) was prepared by mixing corncobs with poly(3-hydroxybutyrate-3-hydroxyvalerate) (PHBV), where the corncobs were pretreated by NaOH or TMAOH. The results of compositional analysis and FTIR showed that both NaOH and TMAOH degraded lignin, hemicellulose and their connection bonds in corncob, thus increased the cellulose content from 39% to 53% and 55%, respectively. The cumulative carbon release from SPC was about 9.3 mg/g and was consistent with both the first-order kinetic and Ritger-Peppas equation. The released organic matters contained low concentration of refractory components. Correspondingly, it showed excellent denitrification performance in simulated wastewater, and the total nitrogen (TN) removal rate was above 95% (influent NO₃^--N was 40 mg/L) and effluent residual chemical oxygen demand (COD) was less than 50 mg/L.

Electrospinning micro-nanofibers immobilized aerobic denitrifying bacteria for efficient nitrogen removal in wastewater

Electrospinning micro-nanofibers with exceptional physicochemical properties and biocompatibility are becoming popular in the medical field. These features indicate its potential application as microbial immobilized carriers in wastewater treatment. Here, aerobic denitrifying bacteria were immobilized on micro-nanofibers, which were prepared using different concentrations of polyacrylonitrile (PAN) solution (8%, 12% and 15%). The results of diameter distribution, specific surface area and average pore diameter indicated that 15% PAN micro-nanofibers with tighter surface structure were not suitable as microbial carriers. The bacterial load results showed that the cell density (OD₆₀₀) and total protein of 12% PAN micro-nanofibers were 107.14% and 106.28% higher than those of 8% PAN micro-nanofibers. Subsequently, the 12% PAN micro-nanofibers were selected for aerobic denitrification under the different C/N ratios (1.5-10), and stable performance was obtained. Bacterial community analysis further manifested that the micro-nanofibers effectively immobilized bacteria and enriched bacterial structure under the high C/N ratios. Therefore, the feasibility of micro-nanofibers as microbial carriers was confirmed. This work was of great significance for promoting the application of electrospinning for microbial immobilization in wastewater treatment.

INFLUENCE OF AEROBIC AND ANAEROBIC SPORTS ON THE TRAINING EFFECTS OF TABLE TENNIS PLAYERS

ABSTRACT Introduction The weakness of cadence and rotation speed in table tennis brings new challenges to the physical strength of young players, presenting a redoubled effort for physical fitness and stability of the shot movements. Objective Study the influence of aerobic and anaerobic exercise on the training effect of table tennis players. Methods 27 young table tennis players aged 9-17 years old from China Table Tennis Institute were selected as the experimental objects. They were divided into 14 in the experimental group for 12 weeks of core strength training and 13 in the control group for 12 weeks of routine physical training. Results There was no significant difference in the control group before and after the experiment (P > 0.05); there was no significant difference in core strength between the experimental group and the control group before the experiment (P > 0.05). Conclusion After the experiment, the core strength of both groups of young table tennis players improved, and the core strength of the experimental group improved significantly from the fourth level to the fifth level of body posture table maintenance. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Molecular mechanisms through which different carbon sources affect denitrification by Thauera linaloolentis: Electron generation, transfer, and competition

Characterizing the molecular mechanism through which different carbon sources affect the denitrification process would provide a basis for the proper selection of carbon sources, thus avoiding excessive carbon source dosing and secondary pollution while also improving denitrification efficiency. Here, we selected Thauera linaloolentis as a model organism of denitrification, whose genomic information was elucidated by draft genome sequencing and KEGG annotations, to investigate the growth kinetics, denitrification performances and characteristics of metabolic pathways under diverse carbon source conditions. We reconstructed a metabolic network of Thauera linaloolentis based on genomic analysis to help develop a systematic method of researching electron pathways. Our findings indicated that carbon sources with simple metabolic pathways (e.g., ethanol and sodium acetate) promoted the reproduction of Thauera linaloolentis, and its maximum growth density reached OD₆₀₀ = 0.36 and maximum specific growth rate reached 0.145 h^-1. These carbon sources also accelerated the denitrification process without the accumulation of intermediates. Nitrate could be reduced completely under any carbon source condition; but in the "glucose group", the maximum accumulation of nitrite was 117.00 mg/L (1.51 times more than that in the "ethanol group", which was 77.41 mg/L), the maximum accumulation of nitric oxide was 363.02 μg/L (7.35 times more than that in the "ethanol group", which was 49.40 μg/L), and the maximum accumulation of nitrous oxide was 22.58 mg/L (26.56 times more than that in the "ethanol group", which was 0.85 mg/L). Molecular biological analyses demonstrated that diverse types of carbon sources directly induced different carbon metabolic activities, resulting in variations in electron generation efficiency. Furthermore, the activities of the electron transport system were positively correlated with different carbon metabolic activities. Finally, these differences were reflected in the phenomenon of electronic competition between denitrifying reductases. Thus we concluded that this was the main molecular mechanism through which the carbon source type affected the denitrification process. In brief, carbon sources with simple metabolic pathways induced higher efficiency of electron generation, transfer, and competition, which promoted rapid proliferation and complete denitrification; otherwise Thauera linaloolentis would grow slowly and intermediate products would accumulate seriously. Our study established a method to evaluate and optimize carbon source utilization efficiency based on confirmed molecular mechanisms.

Effects of iron-based substrate on coupling of nitrification, aerobic denitrification and Fe(II) autotrophic denitrification in tidal flow constructed wetlands

The aerobic properties of nitrification and the anaerobic properties of denitrification in constructed wetlands are difficult to reconcile. In this study, two constructed wetlands were constructed with pyrite and steel slag in combination with zeolite, and their respective nitrification and denitrification capacities were evaluated under different tidal strategies. The steel slag wetland achieved 70.89 % and 46.04 % removal rates of NH₄⁺-N and total nitrogen (TN), and the carbon consumption of denitrification was 1.51 mg BOD/mgN, which was better than pyrite wetland. Microbial analysis showed that Fe(II) autotrophic denitrification and aerobic denitrification occurred in both wetlands, and they were coupled with nitrification to achieve simultaneous removal of NH₄⁺-N and TN. Microbial co-occurrence network and k-core decomposition analysis indicated that the core genus of steel slag wetlands was nitrifying bacteria. This study provides new insights into the application of tidal flow wetlands to treat rural sewage.

Responses of nitrogen removal under microplastics versus nanoplastics stress in SBR: Toxicity, microbial community and functional genes

Microplastics (MPs) and nanoplastics (NPs), as emerging pollutants, are frequently detected in wastewater treatment plants. However, studies comparing the effects of MPs versus NPs on nitrogen removal by activated sludge are rarely reported. Here, the responses of nitrogen removal performance, microbial community and functional genes to MPs and NPs in sequencing batch reactors were investigated. Results revealed that MPs (10 and 1000 μg/L) had no effects on nitrogen removal. While upon exposure to NPs, although low concentration (10 μg/L) of NPs showed no remarkable influence on nitrogen removal, high level (1000 μg/L) of NPs decreased NH₄⁺-N removal efficiency by 24.48% and caused accumulation of NO₃^--N and NO₂^--N. These inhibitory probably due to the acute toxicity of NPs to activated sludge, which was reflected by the increasing reactive oxygen species generation and lactate dehydrogenase release. The toxic effects of NPs further declined the relative abundance of nitrifiers (e.g., Nitrospira) and denitrifiers (e.g., Dechloromonas). These negative effects, accompanied by a decrease in abundance of amoA and nxrA genes related to nitrification (30.01% and 65.24% of control) and narG, nirK and nirS genes associated with denitrification (78.59%, 61.39%, and 86.17% of control), directly illustrated the attenuate phenomenon observed in nitrogen removal.

Biochar fungal pellet based biological immobilization reactor efficiently removed nitrate and cadmium

To efficiently and simultaneously remove nitrate (NO₃^--N) and Cd(II) from aqueous solution, a novel type of biochar fungal pellet (BFP) immobilized denitrification bacteria (Cupriavidus sp. H29) composite was used in a bioreactor. The removal performance of the bioreactor R1 for the initial concentration of 27.7 mg L^-1 nitrate and 10.0 mg L^-1 Cd(II) reached 98.1 and 93.9% respectively, and the inoculation of strain H29 in bioreactor R1 significantly enhanced the removal efficiency of contaminants. The 3D-EEM spectra analysis showed that the activity of microorganisms in the bioreactor was higher at a lower concentration of Cd(II). FTIR indicated the effect of functional groups in BFP in bioadsorption of Cd(II). In addition, high-throughput analysis of species composition of the microbial community in the bioreactors at different levels demonstrated that strain H29 played a significant part in the bioreactor. This research provided a perspective for simultaneous restoration of nitrate and heavy metals in wastewater, and also enriched the application of fungal pellet (FP) in reactors.

Application of external carbon source in heterotrophic denitrification of domestic sewage: A review

The carbon source is essential as an electron donor in the heterotrophic denitrification process. When there is a lack of organic carbon sources in the system, an external carbon source is needed to improve denitrification efficiency. This review compiles the effects of liquid, solid and gaseous carbon sources on denitrification. Sodium acetate has better denitrification efficiency and is usually the first choice for external carbon sources. Fermentation by-products have been demonstrated to have the same denitrification efficiency as sodium acetate. Compared with cellulose-rich materials, biodegradable polymers have better and more stable denitrification performance in solid-phase nitrification, but their price is higher than the former. Methane as a gaseous carbon source is studied mainly by aerobic methane oxidation coupled with denitrification, which is feasible using methane as a carbon source. Liquid carbon sources are better controlled and utilized than solid carbon sources and gaseous carbon sources. In addition, high carbon to nitrogen ratio and hydraulic retention time can promote denitrification, while high dissolved oxygen (DO>2.0 mg L^-1) will inhibit the denitrification process. At the same time, high temperature is conducive to the decomposition of carbon sources by microorganisms. This review also considers the advantages and disadvantages of different carbon sources and cost analysis to provide a reference for looking for more economical and effective external carbon sources in the future.

Denitrification performance and mechanism of denitrification biofilm reactor based on carbon-nitrate counter-diffusional

This study researched denitrification performance and mechanism of denitrification biofilm reactor with different HRTs and carbon sources dosages. Experimental group (EG) had better nitrate and COD removal performance than control group (CG) with different HRTs or carbon doses, and the maximum nitrate-to-nitrite transformation ratio (NTR) of them reached 7.91 ± 1.60% and 17.50 ± 1.92%, respectively. Because organic carbon sources were added to the carrier's interior in EG, forming high local concentrations in biofilms and counter-diffusional with nitrate. By contrast, carbon sources and nitrate were provided from the aqueous phase in CG. Thus, the EG system has more active regions of the biofilm than CG. In addition, EG had higher proportions of microorganisms and enzymes related to denitrification and carbon metabolism. The most dominant phylum, genus, and species were Proteobacteria, Thaurea, and Thauera_sp._27, respectively. The transcript of acetyl-CoA synthetase (K01895) and denitrification (M00529) was mainly originated from unclassified_g__Pseudomonas and unclassified_g__Thauera, respectively.

Effects of various antibiotics on aerobic nitrogen removal and antibiotic degradation performance: Mechanism, degradation pathways, and microbial community evolution

Little information about the selective stress of various antibiotics and how they influence different stages of aerobic nitrogen removal is available. A long-term aerobic nitrogen removal-moving bed biofilm reactor was established by the inoculation of Achromobacter sp. JL9, capable of heterotrophic nitrification and aerobic denitrification, and aerobic activated sludge. The nitrogen removal and antibiotic degradation performances of various antibiotics were then measured. High total nitrogen (91.83% and 91.51%) removal efficiencies were achieved with sulfamethoxazole or no antibiotics, and lower efficiencies were observed with other antibiotics (trimethoprim, teicoplanin, and ciprofloxacin). These results suggest that various antibiotics have different selective inhibitory effects on aerobic nitrogen removal. Additionally, all antibiotics were partly degraded; proposed degradation pathways according to the detected intermediates included ring-opening, S-N bond cleavage, amination, hydroxylation, and methylation. High-throughput sequencing indicated that aerobic denitrifying, recalcitrant pollutant degrading, and antibiotic-resistant bacteria dominate during the community evolution process.

Nitrate removal by alkali-resistant Pseudomonas sp. XS-18 under aerobic conditions: Performance and mechanism

To improve poor nitrate removal by microorganisms under strong alkaline conditions, a new type of aerobic nitrification-reducing bacteria was isolated in this study. Using nitrogen balance and genome information, the capacity of Pseudomonas XS-18 to remove nitrate and the mechanism of alkali tolerance were analyzed. At pH 11.0, XS-18 could remove 12.17 mg N/(L·h) nitrate. At C/N ratios of 13.0 and 25 °C, nitrite and ammonia nitrogen were barely enriched. XS-18 could reduce nitrate through dissimilation and assimilation, and 21.74% and 77.39% of nitrate was converted into cellular components and organic nitrogen, respectively. Meanwhile, functional genes (nirBD, nasAB, gdhA, glnA, and gltBD) associated with nitrogen metabolism were determined. In addition, Na⁺/H⁺ antiporters (MnhACDEFG, PhaACDEFG, NhaCD and TrkAH) and a cell surface protein (SlpA) from the XS-18 genome, as well as compatible solutes that help stabilize intracellular pH, were also characterized. XS-18 possessed significant potential in alkaline wastewater treatment.

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

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

Understanding the impacts of operation mode sequences on the biological aniline degradation system: Startup phase, pollutants removal rules and microbial response

Comparative evaluation of SBRs under different modes (AX/O, AN/AX/O, AN/O/AX, O/AX) with same aniline wastewater arrangements, presenting the startup and performance differences of reactors. The results revealed that the four systems realized the efficient aniline and NH₄⁺-N removal on the basis of sufficient aerobic time. Anaerobic aniline degradation was also achieved in the first three reactors after acclimation. The denitrification efficiency was the highest in O/AX reactor and the lowest in AN/O/AX due to mode sequence setup. Pollutants variations in the typical cycles experimental data combined with microbial diversity analysis were highlighted that aerobic denitrification contributed the most under O/AX mode, while the other three modes relied on anoxic denitrification. Meanwhile, low nitrifiers and aerobic denitrifiers abundance might be another reason for the poor denitrification of AN/O/AX mode. It was inferred that denitrification was most susceptible to operation mode sequences.

Simultaneous nitrogen and carbon removal in a single biological aerated filter by the bioaugmentation with heterotrophic-aerobic nitrogen removal bacteria

ABSTRACTAgrobacterium sp. LAD9 capable of heterotrophic-aerobic nitrogen removal was applied into a single biological aerated filter (BAF) for bioaugmented treatment of municipal wastewater. The achievement of simultaneous nitrogen and carbon removal in the bioaugmented system was systematically evaluated by ratios of COD to nitrogen (COD/N), ranging from 1 to 20. The results showed that at an appropriate COD/N ratio of 10, the BAF exhibited excellent carbon and nutrients removal, the averaged removal efficiencies for COD, NH₄⁺-N and TN were 92.3%, 100% and 80.0%, respectively. Long-term operation of the bioaugmented system also confirmed the stability of the treatment efficiency. Further comparisons of SOUR and PCR-DGGE profiles between the bioaugmented and the control system revealed that the introduction of strain LAD9 greatly changed the structure of original microbial community and facilitated their capabilities of aerobic nutrients removal. The proposed bioaugmentation strategy is of particular importance to upgrading or retrofitting concurrent municipal wastewater treatment systems.

Reed Biochar Addition to Composite Filler Enhances Nitrogen Removal from BDBR Systems in Eutrophic Rivers Channel

With the rapid development of urbanization in China, the eutrophication or black stink of urban rivers has become a critical environmental problem. As a research hotspot in wastewater purification, biofilm technology has shortcomings, such as insufficient carbon sources for denitrification. This study used a Biofilm Denitrification Batch Reactor (BDBR) system constructed using reed biochar as the carbon source required in denitrification, significantly accelerating the biofilm formation. To determine the suitable amount of biochar for water purification from the urban eutrophic rivers by the BDBR system, 0%, 5%, 10%, and 15% reed biochar was added to the viscose fiber combined packing. The combined packing reactor involved in this study had a high removal efficiency of the eutrophication channel COD throughout the experiment. However, adding 5% and 10% biochar in the combined filler effectively increased the number of nitrifying and denitrifying bacteria on the biofilm, improved the dominant bacteria diversity and microbial activity, and enhanced denitrification efficiency in the BDBR system. It provides new ideas and methods for developing and applying in situ denitrification technology for urban polluted rivers.

Organic carbon bioavailability: Is it a good driver to choose the best biological nitrogen removal process?

Organic carbon can affect the biological nitrogen removal process since the Anammox, heterotrophic and denitrifying bacteria have different affinities and feedback in relation to carbon/nitrogen ratio. Therefore, we reviewed the wastewater carbon concentration, its biodegradability and bioavailability to choose the appropriate nitrogen removal process between conventional (nitrification-denitrification) and Anammox-based process (i.e. integrated with the partial nitritation, nitritation, simultaneous partial nitrification and denitrification or partial-denitrification). This review will cover: (i) strategies to choose the best nitrogen removal route according to the wastewater characteristics in relation to the organic matter bioavailability and biodegradability; (ii) strategies to efficiently remove nitrogen and the remaining carbon from effluent in anammox-based process and its operating cost; (iii) an economic analysis to determine the operational costs of two-units Anammox-based process when compared with the commonly applied one-unit Anammox system (partial-nitritation-Anammox). On this review, a list of alternatives are summarized and explained for different nitrogen and biodegradable organic carbon concentrations, which are the main factors to determine the best treatment process, based on operational and economic terms. In summary, it depends on the wastewater carbon biodegradability, which implies in the wastewater treatment cost. Thus, to apply the conventional nitrification/denitrification process a COD_b/N ratio higher than 3.5 is required to achieve full nitrogen removal efficiency. For an economic point of view, according to the analysis the minimum COD_b/gN for successful nitrogen removal by nitrification/denitrification is 5.8 g. If ratios lower than 3.5 are applied, for successfully higher nitrogen removal rates and the economic feasibility of the treatment, Anammox-based routes can be applied to the wastewater treatment plant.

Effects of salinity on the simultaneous anammox and denitrification process: performance, sludge morphology and shifts in microbial communities

In this study, the long-term effects of different salinities on the performance, sludge morphology and shifts in microbial communities were studied in a simultaneous anammox and denitrification (SAD) process at a C/N ratio of 0.5. Stable nitrogen removal efficiencies of 86.96 and 84.58% and nitrogen removal rates of 0.95 and 0.93 kg (m3 d)-1 could be achieved under low (25 mmol l-1) and moderate (50 mmol l-1) salinity, respectively. However, the performance collapsed when the system was exposed to high salinity (100 mmol l-1). The content of extracellular polymeric substances increased as salinity increased, which resulted in larger sizes of granular sludge under low and moderate salinities. Nevertheless, high salinity shock disintegrated granular sludge, thereby decreasing the average granule size. The Illumina-Miseq sequencing results revealed that Candidatus Jettenia was the sole salinity-tolerant AnAOB genus during the entire operation, whereas the main denitrification bacterial genera shifted from Denitrisoma under low salinity to Denitrisoma, Thauera and Ignavibacterium under high salinity. The results of this study provide a comprehensive and practical evaluation of the SAD process for organic nitrogen-rich saline wastewater treatment.

Treatment of a slaughterhouse wastewater by anoxic-aerobic biological reactors followed by UV-C disinfection and microalgae bioremediation

In this study, removal of organic matter and nitrogen from a cattle slaughterhouse wastewater was investigated in a two-stage anoxic-aerobic biological system, followed by UV-C disinfection. Ecotoxicity of the raw, biotreated, and disinfected wastewater against the microalgae Scenedesmus sp. was evaluated in short-term tests, while the potential of the microalgae as a nutrient removal step was addressed in long-term experiments. Throughout 5 operational phases, the biological system was subjected to gradual reduction of the hydraulic retention time (8-1.5 day), increasing the organic (0.21-1.11 kgCOD·m^-3 ·day^-1 ) and nitrogen (0.05-0.28 kgN·m^-3 · day^-1 ) loading rates. COD and total ammoniacal nitrogen (TAN) removal ranged within 83%-97% and 83%-99%, respectively. While providing alkalinity source, effluent TAN concentrations were below 5 mg·L^-1 . Nitrate was the main nitrification product, while nitrite levels remained low (<1 mgN·L^-1 ). Upon supplementation of external COD as ethanol, total nitrogen removal reached up to 90% at the highest load (0.28 kgN·m^-3 ·day^-1 ). After UV-C treatment, 3-log reduction of total coliforms was attained. The 96-hr ecotoxicity tests showed that all non-diluted samples tested (raw, biologically treated and UV-C irradiated wastewater) were toxic to microalgae. Nevertheless, these organisms were able to acclimate and grow under the imposed conditions, allowing to achieve nitrogen and phosphorous removal up to 99.1% and 43.0%, respectively. PRACTITIONER POINTS: The treatment of a slaughterhouse wastewater in an anoxic-aerobic biological system followed by a UV-C disinfection step was assessed. The pre-denitrification system showed efficient simultaneous removal of organic matter and nitrogen from the wastewater under increasing applied loads. UV-C disinfection worked effectively in reducing coliforms from the biotreated effluent, boosting the performance of microalgae on nutrients removal. Despite the toxicity to microalgae, they were capable to acclimate to the aqueous matrices tested, reducing efficiently the nutrients content. The combined stages of treatment presented great capacity for depleting up to 97% COD, 99% nitrogen, and 43% phosphorous.

Autotrophic denitrification in constructed wetlands: Achievements and challenges

The use of constructed wetlands for wastewater treatment is rapidly increasing worldwide due to their advantages of low operating and maintenance costs. Denitrification in constructed wetlands is dependent on the presence of organic carbon sources, and the shortage of organic carbon is the primary hurdle for nitrate removal. Therefore, the use of inorganic electronic donors has emerged as an alternative. This paper provides a comprehensive review of nitrate removal pathways using various inorganic electron donors and the performance and development of autotrophic denitrification in constructed wetlands. The main environmental parameters and operating conditions for nitrate removal in wetlands are discussed, and the challenges currently faced in the application of enhanced autotrophic denitrification wetlands are emphasized. Overall, this review illustrates the need for a deep understanding of the complex interrelationships among environmental and operational parameters and wetland substrates for improving the wastewater treatment performance of constructed wetlands.

A critical review of aerobic denitrification: Insights into the intracellular electron transfer

Aerobic denitrification is a novel biological nitrogen removal technology, which has been widely investigated as an alternative to the conventional denitrification and for its unique advantages. To fully comprehend aerobic denitrification, it is essential to clarify the regulatory mechanisms of intracellular electron transfer during aerobic denitrification. However, reports on intracellular electron transfer during aerobic denitrification are rather limited. Thus, the purpose of this review is to discuss the molecular mechanism of aerobic denitrification from the perspective of electron transfer, by summarizing the advancements in current research on electron transfer based on conventional denitrification. Firstly, the implication of aerobic denitrification is briefly discussed, and the status of current research on aerobic denitrification is summarized. Then, the occurring foundation and significance of aerobic denitrification are discussed based on a brief review of the key components involved in the electron transfer of denitrifying enzymes. Moreover, a strategy for enhancing the efficiency of aerobic denitrification is proposed on the basis of the regulatory mechanisms of denitrification enzymes. Finally, scientific outlooks are given for further investigation on aerobic denitrification in the future. This review could help clarify the mechanism of aerobic denitrification from the perspective of electron transfer.

Effects of static magnetic field on the performances of anoxic/oxic sequencing batch reactor

Two anoxic/oxic (A/O) sequencing batch reactor (SBR) processes were utilized to study the effects of static magnetic field (SMF) on biological wastewater treatment process. Except for conventional indices, the reduced nicotinamide adenine dinucleotide (NADH)/oxidized nicotinamide adenine dinucleotide (NAD⁺) ratio and electron transport system activity (ETSA), as well as poly-beta-hydroxybutyrate (PHB) and extracellular polymetric substance (EPS) contents in two reactors which were with and without SMF under two cyclic times (12 h and 8 h) were monitored. When the process was enhanced by SMF, the total nitrogen removal efficiency can be improved (>80%), and the NADN/NAD⁺ ratio, ESTA, the maximum EPS content and the maximum PHB content in the reactor with SMF were higher. Besides, SMF can reduce the microorganism community diversity and make species distribute more even and abundant. SMF can promote the performance of A/O SBR process via improving electron transport and microbial community.

Effect of temperatures and alternating anoxic/oxic sequencing batch reactor (SBR) operating modes on extracellular polymeric substances in activated sludge

In order to investigate the effect of temperatures and operating modes on extracellular polymeric substances (EPS) contents, three sequencing batch reactors (SBRs) were operated at temperatures of 15, 25, and 35 °C (R_{15 °C}, R_{25 °C}, and R_{35 °C}, respectively), with two SBRs operated under alternating anoxic/oxic conditions (R_A/O and R_O/A, respectively). Results showed that higher contents of tightly bound EPS (TB-EPS) and total EPS appeared in R_{15 °C}, while loosely bound EPS (LB-EPS) dominated in R_{35 °C}. In all three kinds of EPS (LB-EPS, TB-EPS and total EPS) assessed, protein was the main component in R_{15 °C} and R_{25 °C}, while polysaccharides dominated in R_{35 °C}. Moreover, compared with R_O/A, R_A/O was favorable for the production of the three kinds of EPS. Furthermore, three kinds of EPS and their components were augmented during the nitrification process, while they declined during the denitrification process under all conditions except for R_{35 °C}.

Simultaneous removal of nitrate, phosphorous and cadmium using a novel multifunctional biomaterial immobilized aerobic strain Proteobacteria Cupriavidus H29

A novel biomaterial FeCl₃/CaCl₂/KH₂PO₄ modified municipal sludge biochar (FCPC) was synthesized. And the impacts of critical factors such as HRT, temperature and C/N ratio on simultaneous denitrification, dephosphorization and Cd(II) removal were investigated. Results show that the highest nitrate removal efficiency reached 92.22% (8.49 mg·L^-1·h^-1) in test group A and approximately 100% (9.19 mg·L^-1·h^-1) in test group B. Very low phosphate concentrations (approximately 2.50 mg/L) were detected in the effluent. The average removal efficiency of Cd(II) reached 86.40% (4.42 mg·L^-1·h^-1) in experimental group A and 90.15% (4.61 mg·L^-1·h^-1) in experimental group B. Gas emissions and biological precipitation in the bioreactors were monitored, further to confirming contaminant removal mechanisms. Additionally, Cupriavidus H29 was found to contribute dominantly to the FCPC bioreactor activity.

The impact of biodegradable carbon sources on nutrients removal in post-denitrification biofilm reactors

Wastewater from households wastewater treatment plants (HWWTP) is discharged to the ground or to the surface waters. Special consideration should be given to the improvement of HWWTP effectiveness, particularly in relation to nutrients. The addition of biodegradable carbon sources to biofilm reactor, can enhance microbial activity but may also lead to filling clogging. The study aimed to compare 3 different organic substrates: acetic acid (commonly applied)and two untypical - citric acid and waste beer, under the same operational conditions in a post-denitrification biofilm reactor. The study investigated the impact of a type of organic substrate, low pH and time on: (1) biofilm growth, (2) the characteristics of extracellular polymeric substances (EPS), (3) the kinetics of nutrients removal and (4) reactor clogging. Results were referred to (5) the effectiveness of nutrients removal. The study demonstrated that low pH assured the development of a thinbiofilm. Citric acid ensured the lowest biomass volume, being by 53% lower than in the reactor with acetic acid and by as much as 61% lower than in the reactor with waste beer. The soluble EPS fraction prevailed in the total EPS in all reactors. The content of the tightly bound EPS fraction ranged from 26.93% (citric acid) to 36.32% (waste beer). Investigations showed also a high ratio of exoproteins to polysaccharide in all fractions, which indicated a significant role of proteins in developing a highly-proliferating biofilm. The treated wastewater met requirements of Polish regulations concerning COD and nitrogen concentrations.

Deciphering the toxic effects of antibiotics on denitrification: Process performance, microbial community and antibiotic resistance genes

The extensive application of antibiotics, and the occurrence and spread of antibiotic resistance genes (ARGs) shade health risks to human and animal. The long-term effects of sulfamethoxazole (SMX) and tetracycline (TC) on denitrification process were evaluated in this study, with the focus on nitrogen removal performance, microbial community and ARGs. Results showed that low-concentration SMX and TC (<0.2 mg L^-1) initially caused a deterioration in nitrogen removal performance, while higher concentrations (0.4-20 mg L^-1) of both antibiotics had no further inhibitory influences. The abundances of ARGs in both systems generally increased during the whole period, and most of them had significant correlations with intI1, especially efflux-pump genes. Castellaniella, which was the dominant genus under antibiotic pressure, might be potential resistant bacteria. These findings provide an insight into the toxic effects of different antibiotics on denitrification process, and guides future efforts to control antibiotics pollution in ecosystems.

Effects of Hydraulic Retention Time and Influent Nitrate-N Concentration on Nitrogen Removal and the Microbial Community of an Aerobic Denitrification Reactor Treating Recirculating Marine Aquaculture System Effluent

The effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and the microbial community composition of an aerobic denitrification reactor treating recirculating marine aquaculture system effluent were evaluated. Results showed that over 98% of nitrogen was removed and ammonia-N and nitrite-N levels were below 1 mg/L when influent nitrate-N was below 150 mg/L and HRT over 5 h. The maximum nitrogen removal efficiency and nitrogen removal rate were observed at HRT of 6 or 7 h when influent nitrate-N was 150 mg/L. High-throughput DNA sequencing analysis revealed that the microbial phyla Proteobacteria and Bacteroidetes were predominant in the reactor, with an average relative total abundance above 70%. The relative abundance of denitrifying bacteria of genera Halomonas and Denitratisoma within the reactor decreased with increasing influent nitrate-N concentrations. Our results show the presence of an aerobically denitrifying microbial consortium with both expected and unexpected members, many of them relatively new to science. Our findings provide insights into the biological workings and inform the design and operation of denitrifying reactors for marine aquaculture systems.

Simultaneous sulfamethoxazole biodegradation and nitrogen conversion in low C/N ratio pharmaceutical wastewater by Achromobacter sp. JL9

The pharmaceutical industry produces large volumes of low C/N ratio wastewater that is difficult to treat. In this study, we isolated Achromobacter sp. JL9 with high efficiency for sulfamethoxazole degradation and nitrogen conversion in low C/N ratio pharmaceutical wastewater. The SMX biodegradation and nitrogen removal ratio were 92.4% (nitrate-N), 86.7% (ammonia-N), 89.4% (total nitrogen), and 90.4% (SMX). The reaction kinetics and reaction rate constant were C/N ratio-, SMX concentration-, and dissolved oxygen concentration-dependent, and the highest reaction rate constant for SMX biodegradation was 0.0384 min^-1. Gaseous compounds analysis and Nap gene amplification analysis by gas chromatography (GC) and polymerase chain reaction (PCR), respectively, showed N₂ as an end product during nitrogen conversion. Moreover, toxicity assays were conducted by the inhibition percentage (PI) and agar well diffusion methods. The toxicity of the medium gradually decreased, falling within the nontoxic range after 96 h. The present study showed that biological technologies could be an effective, economical, and environmentally friendly remediation against pharmaceutical pollutants.

Insights into the effects of carbon source on sequencing batch reactors: Performance, quorum sensing and microbial community

Effects of carbon source on the performance, quorum sensing (QS) and microbial communities in the sequencing batch reactors were investigated in this work. Among the chosen carbon source, sodium acetate (R1), glucose (R2), starch (R3) and Tween 80 (R4), sodium acetate was the best carbon source for nutrient removal, while starch was favorable for inducing the sludge bulking, and Tween 80 was beneficial to the production of extracellular polymeric substances (EPS) and proliferation of Microthrix parvicella. Additionally, the R² value of linear correlation between sludge settleability and particle size in four reactors followed an order of R1 > R2 > R3 > R4. Moreover, Person correlation analysis showed that various significant correlations were observed in reactors fed with different carbon sources and the QS mainly mediated the production and component of EPS. High-throughput sequencing analysis revealed that the carbon source affected microbial communities and the Canonical correspondence analysis results indicated that QS related to microbial communities. It was inferred that the interactions between microbial communities and QS affected system performance.

Rapid start-up of partial nitritation in aerobic granular sludge bioreactor and the analysis of bacterial community dynamics

The rapid start-up of the partial nitritation process in a laboratory-scale aerobic granular sludge-sequencing batch reactor was successful by controlling low dissolved oxygen and gradually increasing the influent ammonia levels. The microbial community dynamics were analyzed by high-throughput sequencing and quantitative polymerase chain reaction. The microbial communities were significantly affected by the different influent NH₄⁺-N concentrations (77.84, 119.42, 170.31, and 252.21 mg/L) in Phases I, II, III, and IV. The sludge Shannon index in Phases I, II, III, and IV was 3.9, 4.39, 3.47, and 2.13, respectively, which was higher than that of the inoculated sludge (1.62). The dominant class transformed from Alphaproteobacteria and Gammaproteobacteria in Phase I to Betaproteobacteria in Phase IV. Furthermore, Sphingobacteria and Clostridia were the dominant bacteria in Phases III and IV. The quantitative polymerase chain reaction (qPCR) results suggested that Nitrosomonadaceae_uncultured belonging to ammonia-oxidizing bacterium was the dominant species, but the relative abundance of nitrite-oxidizing bacteria (mainly Nitrospira and Nitrobacter) was extremely rare in Phase IV. Furthermore, Thauera, Denitratisoma, and Planctomycetacia were the dominant functional nitrogen removal microbes in Phases III and IV. Some nitrogen removal pathways such as partial nitritation, denitrification, and anaerobic ammonium oxidation co-existed in the partial nitritation process.