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In this work, the modification of Bi2MoO6 with critic acid (CA-BMO) to achieve enhanced adsorption of methylene blue (MB) solution in dark and desorption under visible light irradiation was reported. The as-prepared materials were synthesized by a hydrothermal method and characterized via SEM, FT-IR, XRD, and XPS techniques. Only 16.5% of 10 mg L−1 MB was removed within 10 min by using 0.5 g L−1 Bi2MoO6, while 92.9% removal of MB could be achieved by using 0.5 g L−1 CA-BMO, which enhanced the adsorption removal by a factor of 4.6. The adsorption capacity for MB was 18.9 mg g−1. Desorption efficiency of MB was only observed in CA-BMO system, and it depends on the wavelength of the light source, pH, and the presence of metal ions. Characterization results suggested that carboxyl groups, which were modified onto the surface of Bi2MoO6, could serve as adsorption sites for MB, and the connections were damaged under light, thus leading to the desorption of MB from the surface of the CA-BMO. This study provides a novel reagent-free desorption strategy for dye recovery without secondary pollution, which facilitates the development and application of Bi-based adsorbent for dye-containing wastewater treatment. [ABSTRACT FROM AUTHOR]

Anaerobic microorganisms are thought to play a critical role in regulating the flux of short-chain gaseous alkanes (SCGAs; including ethane, propane and butane) from terrestrial and aquatic ecosystems to the atmosphere. Sulfate has been confirmed to act as electron acceptor supporting microbial anaerobic oxidation of SCGAs, yet several other energetically more favourable acceptors co-exist with these gases in anaerobic environments. Here, we show that a bioreactor seeded with biomass from a wastewater treatment facility can perform anaerobic propane oxidation coupled to nitrate reduction to dinitrogen gas and ammonium. The bioreactor was operated for more than 1000 days, and we used 13C- and 15N-labelling experiments, metagenomic, metatranscriptomic, metaproteomic and metabolite analyses to characterize the microbial community and the metabolic processes. The data collectively suggest that a species representing a novel order within the bacterial class Symbiobacteriia is responsible for the observed nitrate-dependent propane oxidation. The closed genome of this organism, which we designate as 'Candidatus Alkanivorans nitratireducens', encodes pathways for oxidation of propane to CO2 via fumarate addition, and for nitrate reduction, with all the key genes expressed during nitrate-dependent propane oxidation. Our results suggest that nitrate is a relevant electron sink for SCGA oxidation in anaerobic environments, constituting a new microbially-mediated link between the carbon and nitrogen cycles. Anaerobic microorganisms can oxidize short-chain gaseous alkanes such as ethane, propane and butane using sulfate as electron acceptor. Here, the authors show that a bioreactor enrichment of a wastewater microbial community can perform anaerobic propane oxidation coupled to nitrate reduction. [ABSTRACT FROM AUTHOR]

New pollutants, pharmaceuticals and personal care products (PPCPs), accumulate in sewage sludge (SS) in wastewater treatment plants (WWTPs), posing risks to the environment and to human health. In the present study, the fates of typical PPCPs, carbamazepine (CBZ), triclosan (TCS), ibuprofen (IBU) and galaxolide (HHCB), were examined during WW treatment. Additionally, SS collected from a WWTP was used for aerobic composting to investigate the influences of micron-sized Fe 3 O 4 (M-Fe) and nano-sized Fe 3 O 4 (N–Fe) on the degradation of these PPCPs and the succession of microbial communities during the composting process. The results showed that the mean concentrations of CBZ, TCS, IBU and HHCB in the influent of the WWTP were 926.5, 174.4, 8869, and 967.3 ng/g, respectively, and in the effluent were 107.6, 47.0, 283.4, and 88.4 ng/g, respectively. The removal rate averaged ∼80%, while the enrichment rates of the PPCPs in SS ranged from 37.2% to 60.5%. M-Fe and N–Fe reduced NH 3 emissions by 32.9% and 54.1% and N 2 O emissions by 26.2% and 50.8%, respectively. Moreover, the addition of M-Fe and N–Fe effectively increased PPCP degradation rates 1.12–1.66-fold. During the whole process, the additions of M-Fe and N–Fe significantly shifted microbial community structure, and the abundances of Proteobacteria, Chloroflexi, and Actinobacteria were increased during the thermophilic stage, marking them as key PPCP-degrading phyla. Taken together, our results indicated that the addition of M-Fe and N–Fe is an effective method for improving the quality of end compost and accelerating the degradation of PPCPs. The removal rate of the four PPCPs averaged ∼80% after the wastewater treatment plant (WWTP), while the enrichment rates of the PPCPs in sewage sludge (SS) ranged from 37.2% to 60.5%. The M-Fe and N–Fe reduced NH 3 emission by 32.9% and 54.1%, and N 2 O emission by 26.2% and 50.8%, respectively. Meanwhile, adding M-Fe and N–Fe effectively promoted the PPCPs degradation rates by 1.12–1.66 times. During the whole process, the additions of M-Fe and N–Fe significantly shifted the microbial community structure, and the abundances of Proteobacteria, Chloroflexi, and Actinobacteria were boosted during the thermophilic stage, marking as key PPCPs-degrading phyla. [Display omitted] • The enrichment rates of four PPCPs in sewage sludge ranged from 37.2% to 60.5%. • M-Fe and N–Fe reduced NH 3 emission by 32.9% and 54.1%, and N 2 O by 26.2% and 50.8%. • M-Fe and N–Fe effectively promoted the PPCPs degradation rates by 1.12–1.66 time. • M-Fe and N–Fe were effective method to improve compost and PPCPs degradation. [ABSTRACT FROM AUTHOR]

Photosynthetic bacteria (PSB) bioconversion is a new technology for wastewater treatment and resource recovery. The C/N ratio is an important factor in biological wastewater treatment. For the first time, the efficient C/N ratio range for PSB bioconversion, and the effects of the C/N ratio on wastewater treatment efficiency and cell proliferation, were studied. The results of this study showed that PSB bioconversion was efficient when the wastewater C/N ratio was within the range of 400-0.1. Chemical oxygen demand (COD) removal was higher than 60% in this C/N range. The change in the NH4 +-N concentration was fitted by the logistic model for each C/N ratio. The Vmax of nitrogen removal was similar to that of other technologies and it decreased as the C/N ratio decreased. This shows that this technology exhibits reliable pollutant removal in the C/N ratio range of 400-0.1. The nitrogen transformation study indicated that the PSB might use a specific mechanism under a low C/N ratio. PSB cell proliferation was fitted by the logistic model in the C/N ratio range of 400-2, and µmax was found to be not correlated with the C/N ratio. The protein content in the cells was 40-60% in the C/N ratio range of 400-0.1. The results showed that PSB bioconversion technology has a very high resource value and the value of the C/N ratio places little restriction on it. [ABSTRACT FROM AUTHOR]

Abstract: A lignocellulose-based composite hydrogel, as a novel biosorbent, was prepared for Cu2+ removal from wastewater. TEMPO-oxidized cellulose nanofibrils (TOCN) were dispersed in a 7 wt% NaOH/12 wt% urea aqueous solution at room temperature. Meanwhile, the dissolved cellulose was obtained in the same system at subzero temperature. The composite hydrogels were prepared by blending the dissolved cellulose solution, TOCN dispersion, and alkali lignin solution in an NaOH/urea aqueous solution. The composite hydrogel exhibits excellent adsorption capacity for heavy metals, which can be attributed to the synergistic effects of physical adsorption (porous 3D structure) and chemical adsorption (active sites: carboxyl and phenolic groups). The maximum amount of adsorbed Cu2+ onto composite hydrogel can reach 541 mg/g, which was achieved after 45 min. The adsorption behavior is well-described by the pseudo-second-order kinetics and the Freundlich model (R2 > 0.999). Furthermore, the composite hydrogel exhibits high-strength properties, indicating that the presence of TOCN and lignin contributes to mechanical improvements.Graphical abstract: [ABSTRACT FROM AUTHOR]

This paper reviewed systematically the odor production and emissions in wastewater systems including sewer and wastewater treatment plants (WWTP). The subjective and objective characterization of wastewater odor was briefly discussed while the recent literature data of the measured concentrations of various odor compounds is collated with their odor description, threshold value, and human health limits. The extensive compiled data provide a full range of spatial and temporal variations. It was found that hydrogen sulfide, organic sulfur compounds, and aldehydes are the key odorants in sewer emissions. The odor emission from different treatment units of a WWTP are distinct from each other. The primary treatment odor is similar to that from the sewer with high level of hydrogen sulfide. In contrast, the odor from sludge handling units are characterized with high organic compounds and very low level of hydrogen sulfide. Odor from both sewer and WWTP are affected by the operation and environmental conditions. Typical diurnal and seasonal pattern can be observed due to the hydraulic patterns. A prioritization framework is proposed to rank the complicated odorants in wastewater emissions for the design and optimization of treatment and control measures. [ABSTRACT FROM PUBLISHER]

This work evaluates the biodegradation of the antiviral drug acyclovir by an enriched nitrifying culture during ammonia oxidation and without the addition of ammonium. The study on kinetics was accompanied with the structural elucidation of biotransformation products through batch biodegradation experiments at two different initial levels of acyclovir (15 mg L −1 and 15 μg L −1 ). The pseudo first order kinetic studies of acyclovir in the presence of ammonium indicated the higher degradation rates under higher ammonia oxidation rates than those constant degradation rates in the absence of ammonium. The positive correlation was found between acyclovir degradation rate and ammonia oxidation rate, confirming the cometabolism of acyclovir by the enriched nitrifying culture in the presence of ammonium. Formation of the product carboxy-acyclovir (P239) indicated the main biotransformation pathway was aerobic oxidation of the terminal hydroxyl group, which was independent on the metabolic type (i.e. cometabolism or metabolism). This enzyme-linked reaction might be catalyzed by monooxygenase from ammonia oxidizing bacteria or heterotrophs. The formation of carboxy-acyclovir was demonstrated to be irrelevant to the acyclovir concentrations applied, indicating the revealed biotransformation pathway might be the dominant removal pathway of acyclovir in wastewater treatment. [ABSTRACT FROM AUTHOR]

Pharmaceutical residues could potentially pose detrimental effects on aquatic ecosystems and human health, with wastewater treatment being one of the major pathways for pharmaceuticals to enter into the environment. Enhanced removal of pharmaceuticals by ammonia oxidizing bacteria (AOB) has been widely observed in wastewater treatment processes. This article reviews the current knowledge on the biotransformation of pharmaceuticals by AOB. The relationship between the pharmaceuticals removal and nitrification process was revealed. The important role of AOB-induced cometabolism on the biotransformation of pharmaceuticals as well as their transformation products and pathways was elucidated. Kinetics and mathematical models describing the biotransformation of pharmaceuticals by AOB were also reviewed. The results highlighted the high degradation capabilities of AOB toward some refractory pharmaceuticals, with their degradations being clearly related to the nitrification rate and their transformation products being identified, which may exhibit similar or higher ecotoxicological impacts compared to the parent compound. [ABSTRACT FROM AUTHOR]

There is great potential to understand the functional diversity of microorganisms that are involved in waste water treatment through metagenomic analyses. This study presents the first metagenomic comparison of taxonomic and functional profiles of the microbial communities occurring in different aggregates from anaerobic ammonium-oxidizing (anammox) bioreactors. The anammox bacterial communities in both biofilm and granule sludge samples showed relatively high abundance and diversity compared with floccular sludge. Four of the five known genera of anammox bacteria were detected in the three cultures except Candidatus Jettenia, which was absent in the granules. C andidatus Kuenenia comprised the major population of anammox bacteria in these three sludges, independent of their growth morphologies. The genome assembled for the C andidatus Kuenenia in the granule was very similar to the published reference genome of C andidatus K. stuttgartiensis. Genes involved in the metabolism of the anammox process were highly detected in the biofilm and granule sludges. In particular, the abundance of hydrazine synthase gene ( hzs) in the biofilm was around 486 times more pronounced than that in the granules. The knowledge gained in this study highlights an important role of sludge aggregate in affecting community structure and metabolic potential of anammox systems. [ABSTRACT FROM AUTHOR]

This work explores the applicability of clay-polyelectrolyte based hybrid thin films to develop fouling resistant membrane surfaces for wastewater treatment applications. Clay nanoplatelets were layered on a commercial polyethersulfone membrane in conjunction with two oppositely charged polyelectrolytes via the aqueous-based layer-by-layer (LbL) assembly technique. These hybrid nanostructured membranes showed a high degree of fouling resistance as compared to other commercial membranes and the pure polyelectrolyte multilayer (PEM) membranes, when tested against an electrocoagulation-treated high strength wastewater. With the deposition of just 2.25 quadlayers, the clay-PEM (c‐PEM) membranes demonstrated good anti-fouling properties. On crosslinking the polyelectrolytes, the c‐PEM hybrid membranes showed higher reduction in the chemical oxygen demand (COD) value and enhanced fouling resistance as compared to their uncrosslinked counterparts, the pure PEM membranes (both uncross linked and crosslinked) and the bare membrane. However, the high fouling resistance of the c‐PEM membranes was attained at the cost of compromising the high initial flux value of the underlying membrane. Several possible optimization strategies have therefore been suggested in this paper, which can potentially increase the flux of the modified membranes. This work, for the first time, demonstrated an attempt to evaluate the performance of clay-polyelectrolyte nanocomposite membranes against a real wastewater effluent. [ABSTRACT FROM AUTHOR]

Greenhouse gas (GHG) accounting protocols have addressed emissions from wastewater conveyance and treatment using a variety of simplifying methodologies. While these methodologies vary to some degree by protocol, within each protocol they provide consistent tools for organizational entities of varying size and scope to report and verify GHG emissions. Much of the science supporting these methodologies is either limited or the protocols have failed to keep abreast of developing GHG research. This state-of-the-art review summarizes the sources of direct GHG emissions (both those covered and not covered in current protocols) from wastewater handling; provides a review of the wastewater-related methodologies in a select group of popular protocols; and discusses where research has out-paced protocol methodologies and other areas where the supporting science is relatively weak and warrants further exploration. [ABSTRACT FROM AUTHOR]

An integrated system of electrocoagulation and algal cultivation was developed to treat a high strength wastewater—anaerobic digestion liquid effluent for reclaimed water and value-added algal biomass production. The integrated system synergistically takes advantages of both electrocoagulation and algal cultivation to enhance the efficiencies of wastewater treatment. The electrocoagulation treated wastewater had low turbidity with better light penetration (108 NTU) to enable algal growth. The algal cultivation had high removal efficiencies of phosphorus (99.4%) and nitrogen (88.2%). The dissolved iron in the electrocoagulation treated wastewater enhanced lipid accumulation of the algae. The results present that total phosphorus and nitrogen in the reclaimed water were 0.78 g L −1 and 35.5 mg L −1 respectively, and the harvested algal biomass had 35% of lipid, 53% of protein, and 6.4% of carbohydrate. This study concluded a new route for agricultural wastewater treatment that turns wastewater from an environmental liability into a valuable asset. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) can be emitted from wastewater treatment contributing to its greenhouse gas footprint significantly. Mathematical modeling of N 2 O emissions is of great importance toward the understanding and reduction of the environmental impact of wastewater treatment systems. This article reviews the current status of the modeling of N 2 O emissions from wastewater treatment. The existing mathematical models describing all the known microbial pathways for N 2 O production are reviewed and discussed. These included N 2 O production by ammonia-oxidizing bacteria (AOB) through the hydroxylamine oxidation pathway and the AOB denitrification pathway, N 2 O production by heterotrophic denitrifiers through the denitrification pathway, and the integration of these pathways in single N 2 O models. The calibration and validation of these models using lab-scale and full-scale experimental data is also reviewed. We conclude that the mathematical modeling of N 2 O production, while is still being enhanced supported by new knowledge development, has reached a maturity that facilitates the estimation of site-specific N 2 O emissions and the development of mitigation strategies for a wastewater treatment plant taking into the specific design and operational conditions of the plant. [ABSTRACT FROM AUTHOR]

This study focused on developing a membrane-based purification process, coupled with electrocoagulation (EC) as the pretreatment step, to reduce the COD level of an anaerobic digestion effluent. Commercial brackish water reverse osmosis (RO) membranes offer high COD removal but very low water fluxes. In an effort to address this issue, polyelectrolyte multilayer (PEM) membranes were fabricated by the surface modification of loose nanofiltration membranes using layer-by-layer assembly technique. The application of PEM membranes to treat wastewater effluents has not been explored in details. Two polyelectrolyte combinations were tried – the first one consisted of poly (diallyl dimethyl ammonium chloride) and poly (styrene sulfonate) while the second one consisted of poly (allylamine hydrochloride) and poly (acrylic acid). In comparison to commercial RO membranes, these membranes offered significantly higher fluxes, albeit with equivalent COD reduction. The effect of effluent properties like pH and composition, on the performance of these membranes has been discussed. The PEM films were characterized based on properties like thickness and surface charge, which directly affected the separation behavior of the membranes. For the first time, the combination of EC and PEM membranes has been tried out as a simple, energy-efficient two-step process for treating high-strength wastewater. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide is ubiquitously present in many waste streams originating from industrial activities as well as in sewage. It needs to be removed as it is toxic, corrosive, and odorous. Conventional abatement strategies involve physicochemical methods, which require significant amounts of chemicals and/or high energy input. Considering the limitations of physicochemical methods, there is a need for more cost-effective and sustainable abatement strategies. Recent advances in electrode materials and operation have stimulated interest in electrochemical methods for pollutant remediation. Several electrochemical approaches for sulfide abatement have been proposed over the last few years. Electrochemical techniques offer several advantages including the avoidance of dosage, handling, transport and storage of potentially hazardous chemicals, and the possibility of recovering sulfide or sulfur from wastewater as a product. This paper reviews electrochemical strategies that have been proposed for removal of dissolved and gaseous hydrogen sulfide. The advantages and disadvantages as well as the economic potential of each of the proposed methods are discussed. The technical aspects and key challenges to enable full-scale implementation are highlighted. Finally, opportunities for expanding electrochemical methods for sulfide abatement are presented. [ABSTRACT FROM AUTHOR]

Background: Anaerobic digestion has been widely applied to treat the waste activated sludge from biological wastewater treatment and produce methane for biofuel, which has been one of the most efficient solutions to both energy crisis and environmental pollution challenges. Anaerobic digestion sludge contains highly complex microbial communities, which play crucial roles in sludge treatment. However, traditional approaches based on 16S rRNA amplification or fluorescent in situ hybridization cannot completely reveal the whole microbial community structure due to the extremely high complexity of the involved communities. In this sense, the next-generation high-throughput sequencing provides a powerful tool for dissecting microbial community structure and methane-producing pathways in anaerobic digestion. Results: In this work, the metagenomic sequencing was used to characterize microbial community structure of the anaerobic digestion sludge from a full-scale municipal wastewater treatment plant. Over 3.0 gigabases of metagenomic sequence data were generated with the Illumina HiSeq 2000 platform. Taxonomic analysis by MG-RAST server indicated that overall bacteria were dominant (~93%) whereas a considerable abundance of archaea (~6%) were also detected in the anaerobic digestion sludge. The most abundant bacterial populations were found to be Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. Key microorganisms and related pathways involved in methanogenesis were further revealed. The dominant proliferation of Methanosaeta and Methanosarcina, together with the functional affiliation of enzymes-encoding genes (acetate kinase (AckA), phosphate acetyltransferase (PTA), and acetyl-CoA synthetase (ACSS)), suggested that the acetoclastic methanogenesis is the dominant methanogenesis pathway in the full-scale anaerobic digester. Conclusions: In short, the metagenomic sequencing study of this work successfully dissected the detail microbial community structure and the dominated methane-producing pathways of a full-scale anaerobic digester. The knowledge garnered would facilitate to develop more efficient full-scale anaerobic digestion systems to achieve high-rate waste sludge treatment and methane production. [ABSTRACT FROM AUTHOR]

Recent studies have shown that free nitrous acid (FNA) is biocidal to a broad range of microorganisms. Microorganisms residing in anaerobic sewer biofilms were found to be inactivated after a short (6-24 h) exposure to FNA. In this study, we investigate the inactivation kinetics of anaerobic sewer biofilms grown in real wastewater. Microbial viability of biofilms was determined using LIVE/DEAD staining. A two-fraction kinetic model was developed to simulate the inactivation of mixed culture in biofilms. The kinetic parameters were estimated by using Bayesian statistics. Model simulation found that a fraction (85 %) of the biofilm community was highly sensitive to FNA with a high inactivation rate, and a fraction (15 %) was tolerant to FNA and persisted after FNA treatment. This different susceptibility to FNA treatment was likely due to the diverse microbial community and biofilm protection. The fact that nearly 85 % microbes were inactivated confirmed that FNA is a strong biocide to mixed-culture biofilms. It was found that the inactivation rate constant was not affected by pH levels. The kinetic model was successfully used to optimize FNA dosage for sulfide control in sewer biofilms. Also, results suggest that a high FNA concentration is preferred than long exposure time to reduce the total chemical consumption. [ABSTRACT FROM AUTHOR]

The influent chemical oxygen demand (COD) of tomato paste wastewater changes with the quality of the raw material without any evident trend. The required aeration also changes irregularly during treatment. If the actual aeration rate is set at maximum and does not change, the treating cost increases. Thus, an adaptable aeration strategy based on simple data, such as the removal of COD and mixed liquor suspended solids (MLSS), must be established. The plug-flow activated sludge system of Shihezi Tianye Tomato Products Co., Ltd., was used to establish the relationship between the theoretical aeration rates and the removal of COD and MLSS in different regions. The calculation bases of the theoretical aeration rates at different COD loadings were determined. A flexible aeration strategy based on the removal of COD and MLSS was used to analogically calculate and compare the actual aeration patterns from 2010. The proposed method can decrease aeration rate by 8%. [ABSTRACT FROM AUTHOR]

A bacterial strain Pseudomonas sp. a3 capable of degrading nitrobenzene, phenol, aniline, and other aromatics was isolated and characterized. When nitrobenzene was degraded, the release of NH was detected, but not of NO. This result implied that nitrobenzene might have a partial reductive metabolic pathway in strain a3. However, aniline appeared as one of the metabolites during the aerobic degradation of nitrobenzene. Moreover, the appearance of 2-aminophenol during aniline degradation by strain a3 indicated that novel initial reactions existed during the degradation of nitrobenzene and aniline by strain a3. Strain a3 was immobilized in the mixed carrier of polyvinyl alcohol and sodium alginate to improve its degrading efficiency. The optimal concentrations of polyvinyl alcohol and sodium alginate in the mixed carrier were 9 and 3 %, respectively. The immobilized cells had stable degradation activity and good mechanical properties in the recycling tests. The immobilized cells also exhibited higher tolerances in acidic (pH 4-5) and highly saline (10 % NaCl) environments than those of free cells. The biodegradation of nitrobenzene mixed with aniline and phenol using immobilized cells of Pseudomonas sp. a3 was also greatly improved compared with those of free cells. The immobilized cells could completely degrade 300 mg L nitrobenzene within 10 h with 150 mg L aniline and 150 mg L phenol. This result revealed that the immobilized cells of Pseudomonas sp. a3 could be a potential candidate for treating nitrobenzene wastewater mixed with other aromatics. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions from wastewater treatment plants vary substantially between plants, ranging from negligible to substantial (a few per cent of the total nitrogen load), probably because of different designs and operational conditions. In general, plants that achieve high levels of nitrogen removal emit less N2O, indicating that no compromise is required between high water quality and lower N2O emissions. N2O emissions primarily occur in aerated zones/compartments/periods owing to active stripping, and ammonia-oxidizing bacteria, rather than heterotrophic denitrifiers, are the main contributors. However, the detailed mechanisms remain to be fully elucidated, despite strong evidence suggesting that both nitrifier denitrification and the chemical breakdown of intermediates of hydroxylamine oxidation are probably involved. With increased understanding of the fundamental reactions responsible for N2O production in wastewater treatment systems and the conditions that stimulate their occurrence, reduction of N2O emissions from wastewater treatment systems through improved plant design and operation will be achieved in the near future. [ABSTRACT FROM AUTHOR]

Nitrate is one of the chemicals often added to wastewater to control hydrogen sulfide production by sulfate-reducing bacteria (SRB). While the effect of nitrate in various SRB pure cultures is well documented, the effect observed in mixed microbial communities is not consistent. This study investigates the response of mixed SRB communities to nitrate, by examining the changes in activity and community composition of sulfidogenic wastewater biofilm over a 10-day period with 10 mmol L nitrate exposure. Biofilms were enriched in SRB belonging to the Desulfobacter, Desulfobulbus, Desulfomicrobium, and Desulfovibrio genera. Nitrate exposure decreased dsrB transcription within 4 h, and sulfate consumption within 10 days, but it did not fully eliminate sulfide production in the biofilms. The effect of nitrate on SRB was genus specific; Desulfobacter and Desulfobulbus disappeared while Desulfovibrio and Desulfomicrobium persisted in the biofilms. Nitrate exposure also led to the rapid proliferation of nitrate-reducing bacteria within the biofilms, and increased the biofilm thickness. Nitrate consumption began within 2 h of nitrate exposure and gradually increased in rate over time. Transcription of the nitrate reductase napA, and the diversity of nitrate reductase genes narG and napA also increased concurrently. Our results demonstrate that some SRB, presumably those able to tolerate or detoxify nitrite, will persist in sulfidogenic wastewater biofilms despite continuous exposure to high levels of nitrate. Nitrate is therefore unlikely to provide lasting hydrogen sulfide suppression in wastewater biofilms harboring Desulfovibrio or Desulfomicrobium populations. [ABSTRACT FROM AUTHOR]

Abstract: Strain D4 was isolated from the sludge of the wastewater treating system of a 4-Chloronitrobenzene (4-CNB) manufacturer. It was able to utilize 4-CNB as the sole carbon and nitrogen source for growth. Strain D4 was preliminarily identified as Cupriavidus sp. based on its physiological & biochemical characteristics and 16S rRNA gene sequence analysis. It could completely degrade 300 mg L−1 of 4-CNB within 25 h under the condition of 30 °C and pH 7.0. Strain D4 could also degrade 4-CNB in presence of heavy metals including Co2+, Cd2+, Pb2+, Zn2+, Mn2+and so on, therefore it was an excellent candidate for the bio-treatment of 4-CNB and heavy metals co-contaminated environments. The main 4-CNB degrading related genes (cnb A, B, Cab, D, G, Z) and arsenate resistance gene fragment of strain D4 were cloned, sequenced and analyzed, which showed high similarity with the corresponding genes of a reported 4-CNB-degrader, strain CNB-1. The cnb genes of strain D4 were located on two plasmids. This is the first report on the degradation of 4-CNB by the strain from the genus of Cupriavidus sp. [Copyright &y& Elsevier]

Free nitrous acid (FNA) has been identified to be a ubiquitous inhibitor of a wide range of microorganisms, including bacteria involved in wastewater treatment. The FNA-induced inhibition on the anoxic (nitrite as electron acceptor) metabolism of denitrifying poly-phosphate accumulating organisms (DPAOs) was investigated using sludge from a sequencing batch reactor performing carbon, nitrogen, and phosphorus removal from synthetic wastewater. We found that FNA had a much stronger inhibitory effect on phosphorus (P) uptake and glycogen production than on poly-β-hydroxyalkanoate degradation and nitrite reduction. The intracellular adenosine triphosphate levels decreased sharply during the FNA incubation, and the decreasing rates were positively correlated with increasing FNA concentrations. The electron transport activity of DPAOs when exposed to FNA displayed a similar trend. Further, at FNA concentrations above 0.044 mg HNO2-N/L, the anaerobic metabolism of DPAOs was initiated despite of the presence of nitrite, as evidenced by the release of phosphorus and the consumption of glycogen. DPAO metabolism did not recover completely from FNA inhibition in the subsequent FNA-free environment. The recovery rate depended on the concentration of FNA applied in the previous anoxic period. These results suggest that the inhibitory effects are diverse and may be attributable to different mechanisms operating simultaneously. [ABSTRACT FROM AUTHOR]

A sequencing batch reactor (SBR) was used for the treatment of abattoir wastewater to produce effluent with desirable nitrogen and phosphorus levels for irrigation. The SBR cycle consisted of an anaerobic phase with wastewater feeding, a relatively short aerobic period (allowing full ammonium oxidation), a second anoxic period with feeding, followed by settling and decanting. This design of operation allowed biological nitrification and denitrification via nitrite, and therefore with reduced demand for aeration and COD for nitrogen removal. The design also allowed ammonium, rather than oxidized nitrogen, being the primary nitrogen species in the effluent. Biological phosphorus removal was also achieved, with an effluent level desirable for irrigation. A high-level of nitrite accumulation (40 mg N/L) in the reactor caused inhibition to the biological P uptake. This problem was solved through process optimization. The cycle time of the SBR was reduced, with the wastewater load per cycle also reduced, while the daily hydraulic loading maintained. This modification proved to be an effective method to ensure reliable N and P removal. N2O accumulation was measured in two experiments simulating the anoxic phase of the SBR and using nitrite and nitrate respectively as electron donors. The estimated N2O emissions for both experiments were very low. [ABSTRACT FROM AUTHOR]

A new method for the simultaneous online measurement of sulfide and nitrate in wastewater is developed. A UV-VIS spectrometer was used. The sensor was calibrated by means of simultaneous online and offline measurements of sulfide and nitrate in batch tests carried out on a laboratory-scale sewer system. The developed calibration algorithm was successfully validated for both sulfide and nitrate measurement, with confidence limits of 2.7 mg S/L for total dissolved sulfide, and 7.5 mg N/L for nitrate. The online measurement of sulfide and nitrate enabled detailed evaluation of seven nitrate dosing strategies in the laboratory-scale sewer system, providing strong support to process optimisation. The dosage optimisation revealed that nitrate should be added at a location close to the point of sulfide control rather than at the beginning of a rising main, at a rate proportional to the expected hydraulic retention time (HRT) of the wastewater in the sewer section between the point of nitrate addition and the point where sulfide control is desired. [ABSTRACT FROM AUTHOR]

A sequencing batch reactor (SBR) system is demonstrated to biologically remove nitrogen, phosphorus and chemical oxygen demand (COD) to very low levels from abattoir wastewater. Each 6 h cycle contained three anoxic/anaerobic and aerobic sub-cycles with wastewater fed at the beginning of each anoxic/anaerobic period. The step-feed strategy was applied to avoid high-level build-up of nitrate or nitrite during nitrification, and therefore to facilitate the creation of anaerobic conditions required for biological phosphorus removal. A high degree removal of total phosphorus (>98%), total nitrogen (>97%) and total COD (>95%) was consistently and reliably achieved after a 3-month start-up period. The concentrations of total phosphate and inorganic nitrogen in the effluent were consistently lower than 0.2 mg P l-1 and 8 mg N l-1, respectively. Fluorescence in situ hybridization revealed that the sludge was enriched in Accumulibacter spp. (20-40%), a known polyphosphate accumulating organism, whereas the known glycogen accumulating organisms were almost absent. The SBR received two streams of abattoir wastewater, namely the effluent from a full-scale anaerobic pond (75%) and the effluent from a lab-scale high-rate pre-fermentor (25%), both receiving raw abattoir wastewater as feed. The pond effluent contained approximately 250 mg N l-1 total nitrogen and 40 mg P l-1 of total phosphorus, but relatively low levels of soluble COD (around 500 mg l-1). The high-rate lab-scale prefermentor, operated at 37°C and with a sludge retention time of 1 day, proved to be a cheap and effective method for providing supplementary volatile fatty acids allowing for high-degree of biological nutrient removal from abattoir wastewater. [ABSTRACT FROM AUTHOR]

On-line process control may cause substantial changes to the microbial community in a biological wastewater treatment system. Recent studies have shown such effects can be exploited in control system design to achieve an optimised microbial community. Excellent progress has been made on the elimination of nitrite-oxidising bacteria (NOB) in biological nitrogen removal wastewater treatment systems using on-line aeration control, enabling nitrogen removal via the nitrite pathway. Control methods for eliminating NOB are now available for both continuous systems and sequencing batch reactors, and have been demonstrated with both domestic and various types of industrial wastewaters. The elimination or reduced growth of glycogen accumulating organisms (GAOs), a competitor of polyphosphate accumulating organisms (PAOs), in enhanced biological phosphorus removal (EBPR) systems via pH and carbon source control has been conceptually demonstrated through the use of enriched cultures. However, these strategies are not yet ready for the control of practical EBPR processes. Sludge population optimisation also involves selecting the most desirable organism or a consortium of organisms to perform a required function. This is particularly important for nitrification, one of the most important and delicate steps in modern wastewater treatment plants. Results from both experimental and simulation studies suggest that reactor operation could have a major impact on the nitrifier community structure, which should be further investigated in future studies. [ABSTRACT FROM AUTHOR]

A Xanthomonas sp. was isolated from the sludge on the drain outlet of a pharmaceutical factory. Then, the bacterium and carbon nanotubes (CNTs) were co-attached to an oxygen electrode for rapid analysis of biochemical oxygen demand (BOD). The response current was linear with BOD values in the range 10 to 300 mg/L for standard BOD solution with a response time of 35 seconds (R = 0.9994) and 20 to 580 mg/L for pharmaceutical wastewater with a response time ≤200 seconds (R 0.9985), which means that this modified electrode might be used for online SOD analysis of pharmaceutical wastewater. Further studies revealed that the modified electrode can be used for BOD measurement in a high-salt condition. Also, the bacterium/CNTs biofilm can maintain its activity and good performance, even after being sealed and stored at 4°C for 50 days. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen removal via nitrite, as opposed to the traditional nitrate, may be beneficial for carbon-limited biological wastewater treatment plants. However, reliable termination of nitrification at nitrite (nitritation) has proved difficult in the treatment of domestic wastewater. In this study, nitritation was attained in a sequencing batch reactor (SBR) with pre-denitrification treating domestic wastewater (total Kjeldahl nitrogen (TKN) concentration of about 43mgNL−1) by aerobic duration control. The aerobic duration control strategy terminates aeration upon completion of ammonium oxidation with accumulated nitrite still remaining. The SBR was purposefully operated such that the influence of other known selection factors for nitritation was absent. The process proved effective in achieving a steady state whereby over 80% nitritation was sustained. Investigation of the cause of nitritation by a calibrated ammonium and nitrite oxidation model showed aerobic duration control as the key factor leading to nitritation. [Copyright &y& Elsevier]

In enhanced biological phosphorus removal (EBPR) systems, polyphosphate-accumulating organisms (PAOs) are primarily responsible for removing phosphate from wastewater. Propionate is an abundant carbon substrate in many EBPR plants and has been suggested to provide PAOs an advantage over their carbon competitors--the glycogen-accumulating organisms (GAOs). The aerobic metabolism of PAOs enriched with a propionate carbon source is studied in this paper. A metabolic model is proposed and experimentally validated to characterize the aerobic biochemical transformations by PAOs. The model predicts very well the experimental data obtained from the enriched PAO culture through solid-, liquid-, and gas-phase analyses. This model may be combined with previously formulated metabolic models to better describe the biochemical activity of PAOs with acetate and propionate as the primary carbon sources. Furthermore, it can also facilitate the study of the effect of different carbon sources on PAO-GAO competition. Water Environ. [ABSTRACT FROM AUTHOR]

The anaerobic uptake of acetate and propionate as single and dual carbon sources by the putative Defluviicoccus vanus related glycogen accumulating organisms (DvGAOs) is investigated. A high enrichment of DvGAOs, representing 95±3% of the bacterial community bound to the EUBMIX probes, was achieved in a lab-scale reactor operated under alternating anaerobic and aerobic conditions with acetate as the sole carbon source. The culture is able to take up both acetate and propionate under anaerobic conditions, and the metabolism in both cases is well described by the metabolic models previously proposed for GAOs and verified with experimental data obtained with other types of GAO cultures. In the simultaneous presence of acetate and propionate, DvGAOs take up these two carbon sources sequentially, with propionate uptake preceding acetate uptake. Through model-based analysis, we hypothesise that DvGAOs prefer propionate in order to maximise their production of polyhydroxyalkanoates (PHAs) with the same glycogen consumption, which would enhance their growth potential in the following aerobic period. Despite a low to negligible consumption of acetate in the presence of large amounts of propionate, the presence of acetate considerably stimulated the uptake of propionate with the rate increased by over 60% in comparison to the case where only propionate was present. This property enhances the competitive capability of DvGAOs in enhanced biological phosphorus removal (EBPR) wastewater treatment systems, given the fact that wastewater typically contains both acetate and propionate. [Copyright &y& Elsevier]

Two laboratory-scale sequencing batch reactors (SBRs) were operated for enhanced biological phosphorus removal (EBPR) in alternating anaerobic–aerobic or alternating anaerobic–anoxic modes, respectively. Polyphosphate-accumulating organisms (PAOs) were enriched in the anaerobic–aerobic SBR and denitrifying PAOs (DPAOs) were enriched in the anaerobic–aerobic SBR. Fluorescence in situ hybridization (FISH) demonstrated that the well-known PAO, “Candidatus Accumulibacter phosphatis” was abundant in both SBRs, and post-FISH chemical staining with 4,6-diamidino-2-phenylindol (DAPI) confirmed that they accumulated polyphosphate. When the anaerobic–anoxic SBR enriched for DPAOs was converted to anaerobic–aerobic operation, aerobic uptake of phosphorus by the resident microbial community occurred immediately. However, when the anaerobic–aerobic SBR enriched for PAOs was exposed to one cycle with anoxic rather than aerobic conditions, a 5-h lag period elapsed before phosphorus uptake proceeded. This anoxic phosphorus-uptake lag phase was not observed in the subsequent anaerobic–aerobic cycle. These results demonstrate that the PAOs that dominated the anaerobic–aerobic SBR biomass were the same organisms as the DPAOs enriched under anaerobic–anoxic conditions. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 140–148, 2003. [ABSTRACT FROM AUTHOR]

Wastewater treatment is a huge industry worldwide. Despite the massive capital and operating costs, only a relatively small amount of R&D investment is made. This might have been related to the limited demands in terms of effluent quality in the past, but today's environmental awareness requires much stricter effluent standards to be achieved. This in turn should give sufficient incentives, together with the possible large cost savings, to increase the R&D activities in this field. There are certainly significant knowledge gaps to be filled and substantial benefits could be gained from this. A range of knowledge gaps are identified in this paper, extending from the role of intermediates in nutrient removal over parameter estimation in modelling and simulation to understanding the microbial metabolic pathways at a genetic and enzymatic level. These gaps are opportunities and challenges for all researchers and professionals in this field. Addressing them will help substantially in the continuing development of wastewater treatment technologies. The complexity of biological wastewater treatment processes requires a broad range of tools and expertise to address the knowledge gaps. Novel process analysis tools are critically important to investigate biological treatment processes in future. They will come from different expertise areas and will need to be used in close integration to gain maximal benefits from the efforts. These tools will likely include respirometry, novel chemical analyses, microsensors, gene-based identification, microbial physiology techniques and integrated modelling and simulation. Examples of the application of such techniques are provided to demonstrate the way these techniques may be used in future. In the next few years, there is likely an exciting and highly interactive period of research and development for the wastewater industry. [ABSTRACT FROM AUTHOR]

• Influent quality highly affected the overall performance of a WWTP. • WWTP with high strength influent had the lower environmental impact and cost. • Loose effluent standard resulted in the lower cost of a WWTP. • Restricted effluent standard decreased resource recovery potential. Influent concentration and effluent standards have strong impacts on technology selection by wastewater treatment plants (WWTPs) and on resource recovery processes. In this paper, resource recovery simulation scenarios incorporated with conventional WWTP models were designed in an imitation of typical existing facilities. We integrated economic analysis and a life cycle assessment to evaluate the impacts of treatment technologies selected for different influent conditions and effluent standards. The results revealed that high concentration influents required the most complicated treatment processes to meet a strict effluent standard. The pattern of total impacts was strongly dependent on the influent conditions. High concentration influent was found to correlate with low energy consumption, low costs, a high nutrient recovery potential but also a high global warming potential when removing 1 kg of pollutants. The incorporation of resource recovery improved the overall performance of WWTPs; however, low concentration influents were not suitable for resource recovery due to their limited benefits. The strict effluent standard limited the resource recovery potential from wastewater, and a loose effluent standard may improve the resource recovery performance, especially for high concentration influents. [ABSTRACT FROM AUTHOR]

The discovery of denitrifying anaerobic methane oxidation (DAMO) has not only improved our understanding of global methane and nitrogen cycles, but also provided new technology options for removal of nitrate from nitrate-contaminated water. Previous studies have demonstrated DAMO organisms could remove nitrate and nitrite from wastewater under strictly anaerobically conditions. In the study, we investigate the feasibility of nitrate removal from groundwater, which contains dissolved oxygen in addition to nitrate. A membrane biofilm reactor (MBfR), inoculated with DAMO co-culture, was capable of treating synthetic groundwater containing highly contaminated nitrate (50  mg N/L) and oxygen (7–9 mg O 2 /L), with a maximum volumetric nitrate removal rate of 45 mg N/L-d. Accumulations of acetate and propionate were observed in some transient periods, indicating the possible involvement of acetate and propionate as intermediates in methane oxidation. The 16 S rRNA gene amplicon sequencing revealed that Candidatus Methylomirabilis, a known bacterial DAMO organism able to couple nitrite reduction with anaerobic oxidation of methane (AOM), was the dominant population. No archaeal DAMO organisms that are capable of coupling nitrate to AOM were observed, however, considerable amount of denitrifiers were developed in this system. Based on known metabolisms of these microorganisms and a series of batch studies, it was assumed that methane was oxidized into volatile fatty acids (VFAs) under oxygen-limiting conditions, then the generated VFAs served as carbon sources for these heterotrophic denitrifiers to remove nitrate. This study offers a potential technology for nitrate removal from groundwater by DAMO process in MBfR. [ABSTRACT FROM AUTHOR]

[Display omitted] • IWWTPs bacterial communities exhibited a clear species abundance distribution. • Deterministic processes dominate IWWTPs bacterial communities assembly. • Different IWWTPs harbor unique core bacterial community. • IWWTP bacterial community was strongly linked to activated sludge function. Microbial communities are responsible for biological treatment of many industrial wastewater, but our knowledge of their diversity, assembly patterns, and function is still poor. Here, we analyzed the bacterial communities of wastewater and activated sludge samples taken from 11 full-scale industrial wastewater treatment plants (IWWTPs) characterized by the same process design but different wastewater types and WWTP compartments. We found significantly different diversity and compositions of bacterial assemblages among distinct wastewater types and IWWTPs compartments. IWWTPs bacterial communities exhibited a clear species abundance distribution. The dispersal-driven process was weak in shaping IWWTP communities. Meanwhile, environmental and operating conditions were important factors in regulating the structure of the activated sludge community and pollutants removal, indicating that bacterial community was largely driven by deterministic mechanisms. The core microbial community in IWWTPs was different from that in municipal wastewater treatment plants (MWWTPs), and many taxa (e.g. the genus Citreitalea) rarely were detected before, indicating IWWTPs harbored unique core bacterial communities. Furthermore, we found that bacterial community compositions were strongly linked to activated sludge function. These findings are important to both microbial ecologists and environmental engineers, who may optimize the operation strategies jointly for maintaining biodiversity, which in turn may promote a more stable performance of the IWWTP. Overall, our study enhances the mechanistic understanding of the IWWTP microbial community diversity, assembly patterns, and function, and provides important implications for microbial ecology and wastewater treatment processes. [ABSTRACT FROM AUTHOR]

Free nitrous acid (FNA i.e. HNO 2 ) was revealed to be effective in enhancing biodegradability of secondary sludge. Also, nitrite-oxidizing bacteria were found to be more susceptible to FNA than ammonium-oxidizing bacteria. Based on these findings, a novel FNA-based sludge treatment technology is proposed to enhance energy recovery from wastewater/sludge. Energy analysis indicated that the FNA-based technology would make wastewater treatment become an energy generating process (yielding energy at 4 kWh/PE/y; kWh/PE/y: kilowatt hours per population equivalent per year), rather than being a large energy consumer that it is today (consuming energy at 24 kWh/PE/y). Importantly, FNA required for the sludge treatment could be produced as a by-product of wastewater treatment. This proposed FNA-based technology is economically and environmentally attractive, and can be easily implemented in any wastewater treatment plants. It only involves the installation of a simple sludge mixing tank. This article presents the concept of the FNA-based technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Zn substituted Co 3 O 4 catalysts were prepared and applied in PMS activation for florfenicol removal. • The Zn substitution induced electron rearrangement and promoted oxygen vacancies formation in Co 3 O 4. • The Zn substituted Co 3 O 4 (Zn 0.03 Co) exhibited superior florfenicol removal and higher reaction rate than Co 3 O 4. • The florfenicol degradation is highly dependent on PMS/Zn 0.03 Co/florfenicol dosage, temperature and initial pH. • The degradation mechanism and routes were proposed combining LC-MS/MS and theoretical calculation results. Florfenicol (FLO) is a broad-spectrum halogenated antibiotic (containing F and Cl atoms), and the discharged FLO in wastewater exhibits potential biotoxicity. Peroxymonosulfate (PMS) activation can generate reactive oxygen species (ROSs) to realize efficient degradation of organic pollutants. Herein, Zn-substituted Co 3 O 4 (Zn x Co) catalysts were prepared and applied in PMS activation for FLO degradation. The physicochemical properties were systematically studied by combining experiments and density functional theory (DFT) calculation. The Zn partial substitution induced electron rearrangement and promoted oxygen vacancy (OV) formation in Co 3 O 4. Zn 0.03 Co catalyst exhibited superior FLO removal, achieving a higher reaction rate of 0.112 min−1 than Co 3 O 4 (0.053 min−1). The FLO degradation was highly dependent on the factors of PMS/Zn 0.03 Co/FLO dosage, temperature, initial pH, and coexisting inorganic anions. The Zn 0.03 Co also displayed outstanding performance in PMS activation for degradation of various typical organic pollutants. Electron paramagnetic resonance (EPR) spectra and quenching experiments indicated that both radical species ( · OH , SO 4 · - , and · O 2 -) and nonradical species (1O 2) contribute to FLO removal. The redox cycle of Co3+/Co2+ and OVs played an essential role in PMS activation. The electron structure of FLO and parameters of PMS adsorbed on Zn x Co were calculated. The longer length of Co O and O O bonds for the adsorbed PMS could enhance its activation to generate ROSs. The intermediates were detected, and five degradation pathways were proposed. The acute and chronic toxicities of intermediates suggested that the dechlorination process is important for the toxicity attenuation of FLO. This study clarified the performance enhancement mechanism of Zn substitution on FLO degradation by PMS activation using Co 3 O 4 based catalyst, which favors the development of PMS-based advanced oxidation processes for wastewater treatment. [ABSTRACT FROM AUTHOR]

The formation of aerobic granular sludge (AGS) is relatively difficult during the treatment of refractory wastewater, which generally shows small granular sizes and poor stability. The formation of AGS is regulated by N-Acyl homoserine lactones (AHLs)-mediated quorum sensing (QS). However, the potential role of AHLs in AGS formation under the toxic stress of refractory pollutants and the heterogeneity in the distribution and function of AHLs across different aggregates are not well understood. This study investigated the potential effects of AHLs on the formation of AGS during phenolic wastewater treatment. The distribution and succession of AHLs across varying granular sizes and development stages of AGS were investigated. Results showed that AGS was successfully formed in 13 days with an average granular size of 335 ± 39 μm and phenol removal efficiency of >99%. The levels of AHLs initially increased and then decreased. C4-HSL and 3-oxo-C10-HSL were enriched in large granules, suggesting they may play a pivotal role in regulating the concentration and composition of extracellular polymeric substances (EPS). The content of EPS constantly increased to 149.4 mg/gVSS, and protein (PN) was enriched in small and large granules. Luteococcus was the dominant genus constituting up to 62% after the granulation process, and exhibited a strong association with C4-HSL. AHLs might also regulate the bacterial community responsible for EPS production, and pollutant removal, and facilitate the proliferation of slow-growing microorganisms, thereby enhancing the formation of AGS. The synthesis and dynamics of AHLs were mainly governed by AHLs-producing bacterial strains of Rhodobacter and Pseudomonas , and AHLs-quenching strains of Flavobacterium and Comamonas. C4-HSL and 3-oxo-C10-HSL might be the major contributors to promoting sludge granulation under phenol stress and play critical roles in large granules. These findings enhance our understanding of the roles that AHLs play in sludge granulation under toxic conditions. [Display omitted] • C4-HSL and 3-oxo-C10-HSL were mainly involved in granular formation. • Concentration of N-Acyl homoserine lactones (AHLs) in large granules was higher. • Protein was more effective in granules formation as compared to polysaccharides. • AHLs regulating functional microflora contributed to granules formation. • Mechanism of AHLs on granular formation under phenol condition was proposed. [ABSTRACT FROM AUTHOR]

• Stable NOB suppression is maintained in MABR treating low-strength wastewater for > 200 days. • Acidic pH of 5.0–5.2 and in situ FNA of 1 mg N/L jointly result in NOB suppression. • An unprecedentedly high AOB activity at around 2.4 kg N/(m3 d) is achieved at a short HRT of a mere 30 min. • Acid-tolerant AOB in MABR-biofilms show different apparent kinetics and responses to environmental factors. Shortcut nitrogen removal holds significant economic appeal for mainstream wastewater treatment. Nevertheless, it is too difficult to achieve the stable suppression of nitrite-oxidizing bacteria (NOB), and simultaneously maintain the activity of ammonia-oxidizing bacteria (AOB). This study proposes to overcome this challenge by employing the novel acid-tolerant AOB, namely " Candidatus Nitrosoglobus", in a membrane-aerated biofilm reactor (MABR). Superior partial nitritation was demonstrated in low-strength wastewater from two aspects. First, the long-term operation (256 days) under the acidic pH range of 5.0 to 5.2 showed the successful NOB washout by the in situ free nitrous acid (FNA) of approximately 1 mg N/L. This was evidenced by the stable nitrite accumulation ratio (NAR) close to 100 % and the disappearance of NOB shown by 16S rRNA gene amplicon sequencing and fluorescence in situ hybridization. Second, oxygen was sufficiently supplied in the MABR, leading to an unprecedentedly high ammonia oxidation rate (AOR) at 2.4 ± 0.1 kg N/(m3 d) at a short hydraulic retention time (HRT) of a mere 30 min. Due to the counter diffusion of substrates, the present acidic MABR displayed a significantly higher apparent oxygen affinity (0.36 ± 0.03 mg O 2 /L), a marginally lower apparent ammonia affinity (14.9 ± 1.9 mg N/L), and a heightened sensitivity to FNA and pH variations, compared with counterparts determined by flocculant acid-tolerant AOB. Beyond supporting the potential application of shortcut nitrogen removal in mainstream wastewater, this study also offers the attractive prospect of intensifying wastewater treatment by markedly reducing the HRT of the aerobic unit. [Display omitted] [ABSTRACT FROM AUTHOR]

Competition for electrons among different steps of denitrification has previously been shown to occur, and to play an important role in the accumulation and emission of N2O in wastewater treatment. However, this electron competition is not recognized in the current denitrification models, limiting their ability to predict N2O accumulation during denitrification. In this work, a new denitrification model is developed for wastewater treatment processes. It describes electron competition among the four steps of denitrification, through modeling the carbon oxidation and nitrogen reduction processes separately, in contrast to the existing models that directly couple these two types of processes. Electron carriers are introduced to link carbon oxidation, which donates electrons to carriers, and nitrogen oxides reduction, which receives electrons from these carriers. The relative ability of each denitrification step to compete for electrons is modeled through the use of different affinity constants with reduced carriers. Model calibration and validation results demonstrate that the developed model is able to reasonably describe the nitrate, nitrite, and N2O reduction rates of a methanol-utilizing denitrifying culture under various carbon and nitrogen oxides supplying conditions. The model proposed, while subject to further validation, is expected to enhance our ability to predict N2O accumulation in denitrification. [ABSTRACT FROM AUTHOR]