Engineering feasibility, economic viability and environmental sustainability of energy recovery from nitrous oxide in biological wastewater treatment plant

Insights into the individual and combined effects of Cu(Ⅱ) and Ni(Ⅱ) on anammox: nitrogen removal performance, enzyme activity and microbial community

Anaerobic ammonium oxidation (anammox) is an efficient and economical nitrogen removal process for treating ammonium-rich industrial wastewaters. However, Cu(Ⅱ) and Ni(Ⅱ) present in industrial wastewaters are toxic to anaerobic ammonium-oxidizing bacteria (AnAOB). Unfortunately, the effects of Cu(Ⅱ) and Ni(Ⅱ) on anammox have not been thoroughly investigated, especially when Cu(Ⅱ) and Ni(Ⅱ) coexist. This work comprehensively investigated the individual and combined effects of Cu(Ⅱ) and Ni(Ⅱ) on anammox and revealed the inhibitory mechanisms. With the influent NH4+-N and NO2--N concentration of 230 and 250 mg·L-1, the inhibition thresholds on anammox are 2.00 mg·L-1 Cu(Ⅱ), 1.00 mg·L-1 Ni(Ⅱ) and 1.00 mg·L-1 Cu(Ⅱ) + 1.00 mg·L-1 Ni(Ⅱ), and higher Cu(Ⅱ) or Ni(Ⅱ) concentrations resulted in sharp deteriorations of nitrogen removal performance. The inhibition of Ni(Ⅱ) on anammox was mainly attributed to the adverse effect on NiR activity, while the inhibition mechanism of Cu(Ⅱ) seemed to be unrelated to the four functional enzymes, but associated with disruption of cellular and organellar membranes. The behavior of extracellular polymeric substances (EPS) contributed to the antagonistic effect between Cu(Ⅱ) and Ni(Ⅱ) on anammox. In addition, the niche of Candidatus Brocadia and Candidatus Jettenia shifted under the Cu(II) and Ni(II) stress, and Candidatus Jettenia displayed greater tolerance to Cu(II) and Ni(II) stress. In conclusion, this research clarified the combined effect and the inhibitory mechanism of multiple heavy metals on anammox, and provide the guidances for anammox process application in treating high-ammonium industrial wastewaters containing heavy metals.

Nitrous oxide emissions in novel wastewater treatment processes: A comprehensive review

The proliferation of novel wastewater treatment processes has marked recent years, becoming particularly pertinent in light of the strive for carbon neutrality. One area of growing attention within this context is nitrous oxide (N2O) production and emission. This review provides a comprehensive overview of recent research progress on N2O emissions associated with novel wastewater treatment processes, including Anammox, Partial Nitrification, Partial Denitrification, Comammox, Denitrifying Phosphorus Removal, Sulfur-driven Autotrophic Denitrification and n-DAMO. The advantages and challenges of these processes are thoroughly examined, and various mitigation strategies are proposed. An interesting angle that delve into is the potential of endogenous denitrification to act as an N2O sink. Furthermore, the review discusses the potential applications and rationale for novel Anammox-based processes to reduce N2O emissions. The aim is to inform future technology research in this area. Overall, this review aims to shed light on these emerging technologies while encouraging further research and development.

Advances in nitrogen removal and recovery technologies from reject water: Economic and environmental perspectives

This review critically assesses nitrogen removal technologies applied in the reject water treatment, across different stages of technological development, with a focus on their economic and environmental impacts. The prevalent use of biological processes raises concerns due to potential environmental impacts caused by N2O emissions. However, partial nitritation-anaerobic ammonium oxidation demonstrated economic benefits and the potential for positive environmental outcomes when properly operated and controlled. Furthermore, reject water, in many cases, provides sufficient nitrogen concentrations for nitrogen recovery processes, such as ammonia stripping, substituting production of industrial fertilizers and contributing to a circular economy. Nonetheless, their financial competitiveness is subject to various conditions, including the nitrogen concentration or reject water flow. As the environmental benefits of bioprocesses and economic benefits of nitrogen recovery processes may vary, it is crucial to further optimize both and investigate novel promising technologies such as electrochemical systems, denitrifying anaerobic methane oxidation or direct ammonia oxidation.

Visual analysis of greenhouse gas emissions from sewage treatment plants based on CiteSpace: from the perspective of bibliometrics

With the global reduction actions of greenhouse gas (GHG) emissions, environmental facilities, including sewage treatment plants (STPs), need to reduce pollutants while minimizing GHG emissions. Therefore, more and more publications revealed the formation mechanism of GHGs in STPs and committed to finding better reduction schemes. From the perspective of bibliometrics, this study used CiteSpace to conduct quantitative and visual analysis based on 1,543 publications retrieved from Web of Science between 2000 and 2021 around the world. We have systematically evaluated the structure, development trend, hot spots, and research frontier in the field of GHG emissions from STPs and compared with the contents of top journals to verify the scientificity of the analysis. The results show that the number of publications has increased year by year, and the networks of authors and institutions show a strong correlation. Among them, the clusters of nitrous oxide, anaerobic digestion, and life cycle assessment (LCA) started earlier and received extensive attention, which derived other clusters in the research process. With the development of the field, researchers have gradually changed from single water treatment facilities to multi-carriers that can realize energy regeneration and utilization simultaneously. Accordingly, the GHG reduction of STPs through energy regeneration and resource recovery has become a hot point and frontier direction, which also challenges the breakthroughs in relevant technologies. Furthermore, it provides scientific support for the formulation of relevant incentive policies and economic subsidy systems, so as to alleviate the pressure of global warming and realize the sustainable development of STPs concurrently.

Energy and material refineries of future: Wastewater treatment plants

There have been many important milestones on humanity's long journey towards achieving environmental sanitation. In particular, the development of the activated sludge system can be claimed to be one of the most groundbreaking advances in the protection of both public health and the wider ecosystem. The first wastewater treatment plants (WWTPs) were developed over a century ago and were soon configured for use with activated sludge. However, despite their long history and service, conventional activated sludge (CAS) plants have become an unsustainable method of wastewater treatment. In addition, conventional WWTPs are intensive energy-consumers and at best allow only very limited material recovery. A paradigm shift to convert existing WWTPs into more sustainable facilities must therefore be considered necessary and to this end the wastewater biorefinery (WWBR) concept may be considered a solution that maximizes both energy and material recovery, in line with the circular economy approach.

Effect of aeration modes on nitrogen removal and N2O emission in the partial nitrification and denitrification process for landfill leachate treatment

The anoxic/multi-aerobic process is widely applied for treating landfill leachate with low carbon to nitrogen ratio. In this study, the effect of two aeration modes in the aerobic phase, i.e. decreasing dissolved oxygen (DO) and increasing DO, on nitrogen removal and N₂O emission in the process were systematically compared. The results demonstrate that the aerobic phase with increasing DO mode has a positive effect on improved total nitrogen removal (78 %) under the COD/N ratio as low as 3.45 and minimized N₂O emission. DO concentration higher than 1.5 mg/L in the aerobic phase reduced nitrogen removal and led to a significant high N₂O emission in the process. Complete nitrite denitrification in the anoxic phase correlated with minimized N₂O emission. Under efficient nitrogen removal stage, N₂O emission factor was 2.4 ± 1.0 % of the total incoming nitrogen. Microbial analysis revealed that increasing DO mode increased the abundance of ammonia oxidizing bacteria and denitrifiers.

Resource recovery from municipal wastewater: A critical paradigm shift in the post era of activated sludge

The conventional activated sludge (CAS) process as one of the greatest engineering marvels has made irreplaceable contributions towards the human development in the past one hundred years. However, the underlying principle of CAS which is primarily based on biological oxidation has been challenged by accelerating global climate change. In such a situation, a fundamental question that urgently needs to be answered is what wastewater treatment technology would be in the post era of activated sludge? Thus, this article illustrates the necessity of a technology paradigm shift from the current linear economy to circular economy with the energy and resource recovery from municipal wastewater being a major driver. It is argued that ammonium recovery should be considered towards the sustainable municipal wastewater reclamation. Meanwhile, the potential novel processes with enhanced energy and resource recovery are also discussed, which may offer useful insights into the ways to achieve the carbon-neutral municipal wastewater reclamation.

Nitrous oxide emission mitigation from biological wastewater treatment - A review

Nitrous oxide (N₂O) emitted from wastewater treatment processes has emerged as a focal point for academic and practical research amidst pressing environmental issues. This review presents an updated view on the biological pathways for N₂O production and consumption in addition to the critical process factors affecting N₂O emission. The current research trends including the strain and reactor aspects were then outlined with discussions. Last but not least, the research needs were proposed. The holistic life cycle assessment needs to be performed to evaluate the technical and economic feasibility of the proposed mitigation strategies or recovery options. This review also provides the background information for the proposed future research prospects on N₂O mitigation and recovery technologies. As pointed out, dilution effects of the produced N₂O gas product would hinder its use as renewable energy; instead, its use as an effective oxidizing agent is proposed as a promising recovery option.

Development of microalgae-bacteria symbiosis system for enhanced treatment of biogas slurry

In this study, microalgae-bacteria consortia were developed using bacteria and microalgae isolated from biogas slurry for enhanced nutrients recovery and promoted microalgae growth in wastewater. The enhancement rate was introduced to quantify the interaction between bacteria and microalgae. Co-culture of the indigenous microalgae and bacteria could significantly improve the tolerance of microorganisms to pollutants, increase value-added products' production, promote nutrients removal, and reduce carbon emissions compared to mono-culture. The co-culture of Chlorella sp. GZQ001 and Lysinibacillus sp. SJX05 performed best, with its biomass, lipid, protein and fatty acid methyl ester productivities achieved 113.3, 19.2, 40.9 and 3.7 mg·L^-1·d^-1, respectively. The corresponding nutrients removal efficiencies for ammonia nitrogen, total nitrogen, total organic carbon, and total phosphorus were 83.2%, 82.1%, 34.0% and 76.6%, respectively. These results indicated that co-culture of certain indigenous bacteria and microalgae is beneficial to biogas slurry treatment and microalgae growth.

Inducing high nitrite accumulation via modulating nitrate reduction power and carbon flux with Thauera spp. selection

Partial-denitrification (PD, NO₃^--N → NO₂^--N) is emerging as a promising approach for application of anaerobic ammonium oxidation (anammox) process. In this study, stable PD with high nitrite (NO₂^--N) accumulation was achieved by modulating nitrate (NO₃^--N) reduction activity and carbon metabolism. With the influent NO₃^--N increasing from 30 to 200 mg/L, specific NO₃^--N reduction rates (r_no3) were significantly improved, corresponding to the nitrate-to-nitrite transforming ratio (NTR) increasing rapidly to 80.0% within just 70 days. The required COD/NO₃^--N decreased from 4.5 to 2.0 and the carbon flux was more shared in NO₃^--N reduction to NO₂^--N. Notably, Thauera spp. as core denitrifying bacteria was highly enriched with the relative abundance of 70.5%∼82.1% despite different inoculations. This study provided a new insight into inducing high NO₂^--N accumulation and promoting practical application of anammox technology.

Coagulants put phosphate-accumulating organisms at a competitive disadvantage with glycogen-accumulating organisms in enhanced biological phosphorus removal system

Enhanced biological phosphorus removal (EBPR) process is susceptible to the changed operation condition, which results in an unstable treatment performance. In this work, long-term effect of coagulants addition, aluminum salt for the reactor R₁ and iron salt for the reactor R₂, on EBPR systems was comprehensively evaluated. Results showed that during the initial 30 days' coagulant addition, effluent chemical oxygen demand and phosphorus can be reduced below 25 and 0.5 mg·L^-1, respectively. Further supply of metal salts would stimulate microbial extracellular polymeric substance excretion and induce reactive oxygen species accumulation, which destroyed the cell membrane integrity and deteriorated the phosphorus removal performance. Moreover, coagulants would decrease the relative abundance of Candidatus Accumulibacter while increase the relative abundance of Candidatus Competibacter, leading phosphors accumulating organisms in a disadvantage position. The results of this work might be valuable for the operation of chemical assisted biological phosphorus removal bioreactor.

Towards carbon neutrality and water sustainability: An integrated anaerobic fixed-film MBR-reverse osmosis-chlorination process for municipal wastewater reclamation

Freshwater resilience is facing to an increasing challenge, while carbon neutral wastewater reclamation has been put onto agenda in more and more countries. The activated sludge-microfiltration (MF)-reverse osmosis (RO) process has been currently adopted for reclamation of municipal wastewater to high-grade product water (e.g. NEWater). However, the conventional activated sludge (CAS) unit in this process has the drawbacks of excessive sludge generation, high energy consumption, greenhouse gases (GHGs) emissions etc. To address these emerging issues, an integrated anaerobic fixed-film membrane bioreactor (AnfMBR)-RO-chlorination process was developed in this study. Results showed that about 99.9% of COD, 99.3% of phosphate and 95.3% of NH₄⁺-N were removed in the AnfMBR-RO process, while breakpoint chlorination served as a polishing step when the NH₄⁺-N concentration in RO permeate exceeded the typical NH₄⁺-N concentration (e.g. 1 mg/L) of NEWater. The net energy consumption and total GHG emissions in the proposed integrated process were estimated to be 0.33 kWh/m³ and 310.2 g CO₂e/m³ influent wastewater treated, respectively, which were 64% and 74% less than those in the current municipal wastewater reclamation process. Consequently, this study offers an alternative path to bring municipal wastewater reclamation one step closer to carbon neutrality and water sustainability.

Simultaneous partial nitritation, anammox, and denitrification process for the treatment of simulated municipal sewage in a single-stage biofilter reactor

This study provides a feasible scheme for the treatment of municipal sewage through simultaneous partial nitritation, anammox, and denitrification (SNAD) process, which was realized in a single-stage biofilter reactor (BFR). First, the BFR was started up to enrich the anaerobic ammonium-oxidizing bacteria (AnAOB) in the upper part of the reactor through the operation mode of the top influent and bottom effluent. Then, the BFR was inoculated with activated sludge and aerated continuously at the bottom to realize the coupling of SNAD, which was accompanied by a two-point influent from the bottom and top effluent. Results indicated that the high removal efficiency of NH₄⁺-N (93.40%), total nitrogen (TN, 89.95%), and soluble chemical oxygen demand (SCOD, 92.68%) were achieved with an air-water ratio of 4.29 and hydraulic retention time (HRT) of 6 h. During the SNAD steady phase for the treatment of simulated municipal sewage with a soluble chemical organic demand to nitrogen (C/N) ratio of 2.31, low concentrations of NH₄⁺-N (4.13 mg/L), TN (6.44 mg/L), and SCOD (11.29 mg/L) were attained in the effluent. High-throughput sequencing analysis indicated that the relative abundance of Nitrosomonas, Candidatus Brocadia, and Denitratisoma were 0.77%, 0.43%, and 4.07% in the biofilm at the 0-12.5 cm zone, respectively, suggesting successful implementation of the SNAD process.

The Use of Prospect Theory for Energy Sustainable Industry 4.0

Industry 4.0 challenges facilities entrepreneurs to be competitive in the market in terms of energy by rational decision making. The goal of the paper is aimed at introducing Prospect Theory (PT) in Industry 4.0 for making decisions in order to select an optimal energy technology. To reach this goal, an approach for decision making on energy investment has been developed. In this paper, the authors have also provided a new opportunity to apply the new decision making method for strengthening Industry 4.0 by addressing energy concerns based on which rational decisions have been made. The study uses a fuzzy analytical hierarchy process for weighting the evaluation sub-criteria of energy technologies and a modified PT for making decisions related to the selection of one of the investigated technologies. The results show that it is possible to implement PT in Industry 4.0 via a decision making model for energy sustainability. Decision probability was achieved using a behavioral approach akin to Cumulative Prospect Theory (CPT) for the considered technology options. More specifically, the probability has created the same threshold-based decision possibilities. The authors used the case study method based on a company located in North America which produces hardwood lumber. The company uses a heating system containing natural gas-fired boilers. This study has also contributed to the literature on energy sustainable Industry 4.0 by demonstrating a new phenomenon/paradigm for energy sustainability-based Industry 4.0 through using PT. In this context, the main motivation of writing the article has been to promote energy sustainability via complex mechanisms and systems that involve interrelated functions.

Atmospheric methane and nitrous oxide: challenges alongthe path to Net Zero

The causes of methane's renewed rise since 2007, accelerated growth from 2014 and record rise in 2020, concurrent with an isotopic shift to values more depleted in ¹³C, remain poorly understood. This rise is the dominant departure from greenhouse gas scenarios that limit global heating to less than 2°C. Thus a comprehensive understanding of methane sources and sinks, their trends and inter-annual variations are becoming more urgent. Efforts to quantify both sources and sinks and understand latitudinal and seasonal variations will improve our understanding of the methane cycle and its anthropogenic component. Nationally declared emissions inventories under the UN Framework Convention on Climate Change (UNFCCC) and promised contributions to emissions reductions under the UNFCCC Paris Agreement need to be verified independently by top-down observation. Furthermore, indirect effects on natural emissions, such as changes in aquatic ecosystems, also need to be quantified. Nitrous oxide is even more poorly understood. Despite this, options for mitigating methane and nitrous oxide emissions are improving rapidly, both in cutting emissions from gas, oil and coal extraction and use, and also from agricultural and waste sources. Reductions in methane and nitrous oxide emission are arguably among the most attractive immediate options for climate action. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

Circular economy-driven ammonium recovery from municipal wastewater: State of the art, challenges and solutions forward

In current biological nitrogen removal (BNR) processes, most of ammonium in municipal wastewater is biologically transformed to nitrogen gas, making ammonium recovery impossible. Thus, this article aims to provide a holistic review with in-depth discussions on (i) current BNR processes for municipal wastewater treatment, (ii) environmental and economic costs behind ammonium in municipal wastewater, (iii) state of the art of ammonium recovery from municipal wastewater including anaerobic membrane bioreactor turning municipal wastewater to a liquid fertilizer, capturing ammonium in phototrophic biomass, waste activated sludge for land application, bioelectrochemical systems, biological conversion of ammonium to nitrous oxide as a fuel oxidizer, and adsorption, (iv) feasibility and challenge of adsorption for ammonium recovery from municipal wastewater and (v) innovative municipal wastewater reclamation processes coupled with ammonium recovery. Moving forward, municipal wastewater reclamation and resource recovery should be addressed under the framework of circular economy.

Enhanced recovery of nitrous oxide from incineration leachate in a microbial electrolysis cell inoculated with a nosZ-deficient strain of Pseudomonas aeruginosa

High concentrations of nitrous oxide were recovered from partial nitrification treated leachate in a microbial electrolysis cell (MEC) inoculated with a nosZ-deficient strain of Pseudomonas aeruginosa. N₂O conversion efficiencies > 90% were achieved when a potential of 0.8 V was applied to the MEC. The ΔnosZ strain was enriched in the 0.8 V MEC, but Achromobacter dominated the non-current control. Nitric oxide reductase genes were highly expressed by ΔnosZ cells growing in the 0.8 V MEC, consistent with enhanced nitrous oxide production rates. Concentrations of phenazine derivatives and transcripts from phenazine biosynthesis genes were also high in the 0.8 V MEC. Phenazine derivatives are known to act as electron shuttles, enhance biofilm formation, and help ward off competitors, thereby increasing the survivability of the ΔnosZ strain in the MEC. These results show that applied current stabilized growth of the ΔnosZ strain in the reactor and allowed it to sustainably generate high concentrations of nitrous oxide.

Insights into chronic zinc oxide nanoparticle stress responses of biological nitrogen removal system with nitrous oxide emission and its recovery potential

The nitrogen transformation performances and greenhouse gas nitrous oxide (N₂O) emissions in a sequencing batch reactor under chronic exposure to zinc oxide nanoparticles (ZnO NPs) were quantified and the system's self-recovery potentials were assessed. ZnO NPs posed a dose-dependent depression effect on the removal efficiencies of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN), and the N₂O emissions. The suppressed N₂O emissions had a positive relationship with the activity ratios of nitrite/NO reductases and N₂O reductase, and were expected to be caused by the inhibited heterotrophic denitrification process. The inhibition of glucose metabolism key enzymes and electron transport chain activities would be responsible for the heterotrophic denitrification performances deterioration. Furthermore, the removal efficiencies of NH₄⁺-N and TN were recovered to control levels through the nitrite-shunt. However, the N₂O emission increased significantly above the control during the recovery period mainly due to the irreversibility of the depressed nitrite oxidation activities.

Microalgal-bacterial granular sludge process outperformed aerobic granular sludge process in municipal wastewater treatment with less carbon dioxide emissions

The aerobic granular sludge (AGS) process and microalgal-bacterial granular sludge (MBGS) process were comparably applied for municipal wastewater treatment in sequencing batch reactors with a height to diameter ratio of eight. For morphological appearances, the yellow aerobic granules were strip-shaped (4.0 mm × 0.62 mm) while the green microalgal-bacterial granules were elliptical-shaped (2.0 mm × 0.75 mm). The dominated rod-shaped bacteria (e.g., Acidobacteria and Bacteroidetes) and the slender configuration might be associated with the strip shape of aerobic granules under weak acid conditions. The nutrients removal performances by MBGS process were generally slightly better than AGS process. In addition, nutrients removal mechanisms were identified to elucidate how organics, ammonia, and phosphorus were removed by AGS process and MBGS process, respectively. Mass balance calculation estimated that MBGS process appeared to achieve much less CO₂ emission (5.8%) compared with AGS process (44.4%). Overall, it proved that MBGS process, with the merits of potentially low energy cost, limited CO₂ emission, and excellent performance, showed more prospects in municipal wastewater treatment than AGS process.

Expand, relocate, or underground? Social acceptance of upgrading wastewater treatment plants

Securing a moderate level of social acceptance for obnoxious facilities, public facilities that have negative effects, such as odors, noise, or other disruptions, is critical to infrastructure plans. For wastewater treatment plant (WWTP), also obnoxious facilities, upgrading and expanding the capacity of existing WWTP, are more important than the construction of new plants, in some regions. This study analyzes and compares the social acceptance of different types of WWTP upgrades and capacity expansion projects. Contingent valuation method is used to elicit South Korean households' willingness to pay (WTP) for preventing the expansion of a WWTP. The aggregated WTP is interpreted from the perspective of social conflict costs. The results show that the annual mean WTP of South Korean households to prevent WWTP expansion ranges from KRW 32,058 (US $27.61) to KRW 45,793 (US $39.44) depending on spatial location, which implies that the social conflict costs for the WWTP expansion in South Korea are considerable. It is also found that an underground WWTP at current site is a best alternative to lower the social conflict costs; it is even better than relocation an existing WWTP to another area. Several related policy implications are provided based on the analysis results.

Catalytic pyrolysis of rain tree biomass with nano nickel oxide synthetized from nickel plating slag: A green path for treating waste by waste

Catalytic pyrolysis of rain tree biomass (RTB), a typical horticultural waste, was investigated with nano-NiO as catalyst produced from hazardous nickel plating slag (NPS). It appeared from the analyses by FTIR, TGA, XRD, BET, and FESEM/EDX that nano-NiO produced had a S_BET and mean particle size of 53.4 m²/g and 112.3 nm. The catalytic pyrolysis kinetics of RTB with and without catalyst were studied by Friedman method. It was found that the activation energy (E_a) was in the range of 177 to 360 kJ/mol at a conversion rate of 0.1 - 0.75. The results further revealed that the H₂ increase ratio in pyrolysis above 500 °C was more than 40% in the presence of catalyst. Consequently, this study showed the great potential of nano-NiO as a high-efficiency catalyst in recovering energy from biomass.

Deciphering correlation between chromaticity and activity of anammox sludge

The red color is the most striking character of anaerobic ammonium-oxidizing bacteria (AnAOB) which has been used to estimate the anammox activity roughly. However, the quantitative relationship between the color and activity of anammox sludge still remains unknown. In this study, the chromaticity, activity and their correlation were systematically investigated at different steady-state nitrogen loading rates. The chromaticity of anammox sludge was digitalized by the CIE L*a*b* color space. The results revealed that the average chroma value was found to be significantly correlated with specific anammox activity (r = 0.940, p < 0.01) and the cluster centers of chromaticity coordinates (a*, b*) of anammox sludge were established to define the typical working states of anammox system. The visible spectra of anammox sludge were proved to originate from the cytochrome c. The correlation between chroma and heme c concentration of anammox sludge was consistent with the fully-reduced cytochrome c and the chroma was determined by both content and redox ratio of cytochrome c. The chromaticity of anammox sludge was able to be linked with the anammox activity via reduced cytochrome c content. The gene abundance of cytochrome c synthetase linked the chromaticity with AnAOB quantity via total cytochrome c content, while the enzyme activity of octaheme hydrazine dehydrogenase linked the chromaticity with AnAOB activity via reduced cytochrome c ratio. Moreover, the redundancy analysis proved that heme c, as the key component of cytochrome c, was the most important explanatory variable accounting for the maximum 69.6% of the total variation of the anammox community, which correlated positively with the relative abundance of dominant AnAOB (Candidatus Kuenenia). This work aimed at demonstrating the chromaticity of anammox sludge could be developed as an alternative intuitive anammox activity indicator which will promote the monitoring and optimization of anammox process.

Effect of NaCl Concentration on Microbiological Properties in NaCl Assistant Anaerobic Fermentation: Hydrolase Activity and Microbial Community Distribution

Previous studies have demonstrated that sludge hydrolysis and short-chain fatty acids (SCFAs) production were improved through NaCl assistant anaerobic fermentation. However, the effect of NaCl concentrations on hydrolase activity and microbial community structure was rarely reported. In this study, it was found that α-glucosidase activity and some carbohydrate-degrading bacteria were inhibited in NaCl tests, owing to their vulnerability to high NaCl concentration. Correspondingly, the microbial community richness and diversity were reduced compared with the control test, while the evenness was not affected by NaCl concentration. By contrast, the protease activity was increased in the presence of NaCl and reached the highest activity at the NaCl concentration of 20 g/L. The protein-degrading and SCFAs-producing bacteria (e.g., Clostridium algidicarnis and Proteiniclasticum) were enriched in the presence of NaCl, which were salt-tolerant.

Resuscitation, isolation and immobilization of bacterial species for efficient textile wastewater treatment: A critical review and update

Given highly complex and recalcitrant nature of synthetic dyes, textile wastewater poses a serious challenge on surrounding environments. Until now, biological treatment of textile wastewater using efficient bacterial species is still considered as an environmentally friendly and cost-effective approach. The advances in resuscitating viable but non-culturable (VBNC) bacteria via signaling compounds such as resuscitation-promoting factors (Rpfs) and quorum sensing (QS) autoinducers, provide a vast majority of potent microbial resources for biological wastewater treatment. So far, textile wastewater treatment from resuscitating and isolating VBNC state bacteria has not been critically reviewed. Thus, this review aims to provide a comprehensive picture of resuscitation, isolation and application of bacterial species with this new strategy, while the recent advances in synthetic dye decolorization were also elaborated together with the mechanisms involved. Discussion was further extended to immobilization methods to tackle its application. We concluded that the resuscitation of VBNC bacteria via signaling compounds, together with biochar-based immobilization technologies, may lead to an appealing biological treatment of textile wastewater. However, further development and optimization of the integrated process are still required for their wide applications.

A self-sustaining synergetic microalgal-bacterial granular sludge process towards energy-efficient and environmentally sustainable municipal wastewater treatment

Globally increasing concerns have been raised on the high energy consumption and greenhouse gas emissions in conventional municipal wastewater treatment processes over the past decades. In this study, a self-sustaining synergetic microalgal-bacterial granular sludge process was thus developed to address these challenges. The results showed that the microalgal-bacterial granular sludge process was capable of removing 92.69%, 96.84% and 87.16% of influent organics, ammonia and phosphorus under non-aeration conditions over a short time of 6 h. The effluent could meet the increasingly stringent discharge standards in many countries worldwide. A tight synergetic interrelationship effect between microalgae and bacteria in granules was essential for such excellent process performance. The stoichiometric and functional genes analyses further revealed that most of organic matter and nutrients were removed through microalgal and bacterial assimilations. Moreover, it was found that there existed a desirable distribution of functional species of microalgae and bacteria in microalgal-bacterial granules, which appeared to be essential for the self-sustaining synergetic reactions and stability of microalgal-bacterial granules. Consequently, this work may offer a promising engineering alternative with great potential to achieve energy-efficient and environmentally sustainable municipal wastewater treatment.

Flexible Nitrite Supply Alternative for Mainstream Anammox: Advances in Enhancing Process Stability

Anaerobic ammonium oxidation (anammox) has attracted extensive attention as a potentially sustainable and economical municipal wastewater treatment process. However, its large-scale application is limited by unstable nitrite (NO₂^--N) production and associated excessive nitrate (NO₃^--N) residue. Thus, our study sought to evaluate an efficient alternative to the current nitritation-based anammox process substituting NO₂^--N supply by partial-denitrification (PD; NO₃^--N → NO₂^--N) under mainstream conditions. Ammonia (NH₄⁺-N) was partly oxidized to NO₃^--N and removed via a PD coupled anammox (PD/A) process by mixing the nitrifying effluents with raw wastewater (NH₄⁺-N of 57.87 mg L^-1, COD of 176.02 mg L^-1). Excellent effluent quality was obtained with< 5 mg L^-1 of total nitrogen (TN) despite frequent temperature fluctuations (25.7-16.3 °C). The genus Thauera (responsible for PD) was the dominant denitrifiers (36.4%-37.4%) and coexisted with Candidatus Brocadia (anammox bacteria; 0.33%-0.46%). The efficient PD/A allowed up to 50% reduction in aeration energy consumption, 80% decrease in organic resource demand, and lower nitrous oxide (N₂O) production compared to conventional nitrification/denitrification process. Our study demonstrates that coupling anammox with flexible NO₂^--N supply has great potential as a stable and efficient mainstream wastewater treatment.

Recent advancement on biological technologies and strategies for resource recovery from swine wastewater

Swine wastewater is categorized as one of the agricultural wastewater with high contents of organics and nutrients including nitrogen and phosphorus, which may lead to eutrophication in the environment. Insufficient technologies to remove those nutrients could lead to environmental problems after discharge. Several physical and chemical methods have been applied to treat the swine wastewater, but biological treatments are considered as the promising methods due to the cost effectiveness and performance efficiency along with the production of valuable products and bioenergies. This review summarizes the characteristics of swine wastewaters in the beginning, and briefly describes the current issues on the treatments of swine wastewaters. Several biological techniques, such as anaerobic digestion, A/O process, microbial fuel cells, and microalgae cultivations, and their future aspects will be addressed. Finally, the potentials to reutilize biomass produced during the treatment processes are also presented under the consideration of circular economy.

The Co-occurrence of DNRA and Anammox during the anaerobic degradation of benzene under denitrification

It was revealed that Anammox process promotes the anaerobic degradation of benzene under denitrification. This study investigates the effect of dissimilatory nitrate reduction to ammonium (DNRA) and exogenous ammonium on anaerobic ammonium oxidation bacteria (AnAOB) during the anaerobic degradation of benzene under denitrification. The results indicate that anammox occurs synergistically with organisms using the DNRA pathway, such as Draconibacterium and Ignavibacterium. Phylogenetic analysis showed 64% (16/25) and 36% (5/25) hzsB gene sequences, a specific biomarker of AnAOB, belonged to Candidatus 'Brocadia fuldiga' and Candidatus 'Kuenenia', respectively. Exogenous ammonium addition enhanced the anammox process and accelerated benzene degradation at a 1.89-fold higher average rate compared to that in the absence of exogenous ammonium and AnAOB belonged to Ca. 'Kuenenia' (84%) and Ca. 'Brocadia fuldiga' (16%). These results indicate that Ca. 'Brocadia fuldiga' could also play a role in DNRA. However, the diversity of abcA and bamA, the key anaerobic benzene metabolism biomarkers, remained unchanged. These findings suggest that anammox occurrence may be coupled with DNRA or exogenous ammonium and that anammox promotes anaerobic benzene degradation under denitrifying conditions. The results of this study contribute to understanding the co-occurrence of DNRA and Anammox and help explore their involvement in degradation of benzene, which will be crucial for directing remediation strategies of benzene-contaminated anoxic environment.

Nitrous oxide production from wastewater treatment: The potential as energy resource rather than potent greenhouse gas

Nitrous oxide (N₂O), produced from wastewater treatment, is a potent greenhouse gas and has become a global concern in recent years. However, N₂O has also been commonly used as a powerful oxidant for energy generation. As such, an increasing effort has been devoted to explore the energy potential of N₂O from wastewater treatment processes recently. Nevertheless, the holistic knowledge on energy recovery from nitrogen in wastewater is still lacking for facilitating its further development. Striving for sustainable wastewater treatment, this review paper aimed to give the up-to-date status on several essential aspects regarding the N₂O recovery as an energy resource rather than emission as a greenhouse gas, including energy production via N₂O decomposition, main biotic N₂O production sources, the potential bioprocesses used for N₂O recovery, and the possible N₂O harvesting strategies. We then put forward perspectives for N₂O recovery and future challenges to improve our understanding of the energy generation, microbial processes involved and harvesting approaches in order to potentially achieve sustainable wastewater treatment via N₂O recovery.

Mechanisms of nitrous oxide emission during photoelectrotrophic denitrification by self-photosensitized Thiobacillus denitrificans

Photoelectrotrophic denitrification (PEDeN) using bio-hybrids has the potential to remove nitrate (NO₃^-) from wastewater in an economical and sustainable way. As a gas of global concern, the mechanisms of nitrous oxide (N₂O) emissions during this novel process remain unclear. Herein, a self-photosensitized bio-hybrid, i. e., Thiobacillus denitrificans-cadmium sulfide, was constructed and the factors affecting N₂O emissions during PEDeN by the bio-hybrids were investigated. The system was sensitive to the input NO₃^--N and NO₂^--N, resulting in changes in the N₂O/(N₂+N₂O) ratio from 1% to 95%. In addition to free nitrous acid (FNA), reactive oxidative species (ROS) were a unique factor affecting N₂O emission during PEDeN. Importantly, the N₂O reduction step exhibited greater susceptibility to the ROS than nitrate reduction step. The contributions of hydrogen peroxide (H₂O₂), superoxides (O₂^-•), hydroxyl radicals (•OH) and FNA to the inhibition of N₂O reduction were >15.0%, >5.4%, 1.3%, and <70.2%, respectively for a reduction of 13.5 mg/L NO₃^--N. A significant down-regulation of the relative transcription of the gene nosZ demonstrated that the inhibition of N₂O reductase occurred at the gene level. This finding has important implications not only for mitigating N₂O emissions during the PEDeN process but also for encouraging a reexamination process of N₂O emissions in nature, particularly in systems in which ROS are present during the denitrification process.

A review on mainstream deammonification of municipal wastewater: Novel dual step process

The conventional biological nitrogen removal process is receiving increasing pressure partially due to its energy-negative operation. To address this challenge, various mainstream deammonification processes have been explored for energy-neutral municipal wastewater treatment, whereas these processes appear challenging to be sustainably and stably achieved in conventional process configurations. Therefore, this review aimed to provide a comprehensive analysis of the state-of-the-art of mainstream deammonification, while highlighting the major technical challenges. It appeared that recently developed novel dual step process, i.e. A-B processes, could provide a feasible engineering option for mainstream deammonification, where A-stage is designed for COD capture with the aim to enhance energy recovery, and B-stage is tailored for nutrient removal/recovery. This indeed may lead to a promising integrated mainstream deammonification process towards energy-efficient and environmentally sustainable nitrogen removal. Meanwhile, this review also offered an opinion on future municipal wastewater treatment, aiming for concurrent water reclamation and energy recovery.

Effective decolorization of anthraquinone dye reactive blue 19 using immobilized Bacillus sp. JF4 isolated by resuscitation-promoting factor strategy

Given the highly complex recalcitrant nature of synthetic dyes, biological treatment of textile wastewater using efficient bacterial species is still considered as an environmentally friendly manner. In this study, a reactive blue 19 (RB19)-degrading strain, Bacillus sp. JF4, which was isolated by resuscitation-promoting factor (Rpf) strategy, was immobilized into polyvinyl alcohol-calcium alginate-activated carbon beads (JF4-immobilized beads) for RB19 decolorization. Results suggest that the JF4-immobilized beads, which were capable of simultaneous adsorption and biodegradation, showed a high decolorization activity, while they exhibited better tolerability towards high RB19 concentrations. The JF4-immobilized beads could almost completely decolorize 100 mg/L RB19 within 10 d, while only 92.1% was decolorized by free bacteria within 12 d. Further investigation on the equilibrium and kinetics of the adsorption process suggests that the pseudo-second-order model best fit the adsorption kinetics data, and the Freundlich isotherm was the most suitable for the description of the equilibrium data. Notably, the repeated batch cycles indicated that complete decolorization of 100 mg/L RB19 by JF4-immobilized beads can be maintained for at least three cycles without much reduction in efficiency. These findings suggest that immobilizing Rpf-resuscitated strain into beads was an effective strategy for textile wastewater treatment.

Establishing a Sustainable Sports Tourism Evaluation Framework with a Hybrid Multi-Criteria Decision-Making Model to Explore Potential Sports Tourism Attractions in Taiwan

In recent years, the awareness of sustainable tourism has risen around the world. Many tourism industries combine sports to attract more customers to facilitate the development of the economy and the promotion of local culture. However, it is an important task to establish a comprehensive tourism evaluation framework for sustainable sports tourism. This study proposes a Multi-Criteria Decision-Making (MCDM) model to discuss the above issues, using the Bayesian Best Worst Method (Bayesian BWM) to integrate multiple experts’ judgments to generate the group optimal criteria weights. Next, the modified Visekriterijumska Optimizacija i Kompromisno Resenje (VIKOR) technique is combined with the concept of aspiration level to determine the performance of sports attractions and their priority ranks. In addition, this study adds a perspective of institutional sustainability to emphasize the importance of government support and local marketing. The effectiveness and robustness of the proposed model is demonstrated through potential sports tourism attractions in Taiwan. A sensitivity analysis and models comparison were also performed in this study. The results show that the proposed model is feasible for practical applications and that it effectively provides some management implications to support decision-makers in formulating improvement strategies.

A novel micro-ferrous dosing strategy for enhancing biological phosphorus removal from municipal wastewater

Ferrous salts have been widely used to enhance phosphorus removal in full-scale wastewater treatment plants, with an average dosage of 0.24-0.35 mM. However, such high dosage inevitably caused serious concerns on operation, potential biological toxicity and excessive sludge production. Thus, this study investigated the effect of micro-dosing of ferrous salt at the level of 0.02 mM on enhanced biological phosphorus removal (EBPR) in sequencing batch reactors. Results showed that micro-dosing of ferrous salt enhanced the overall performance, with average COD, TN and TP removal of more than 4.2%, 2.0% and 5.8%, respectively. In addition, the sequencing analysis further revealed that micro-ferrous dosing could significantly improve the diversity and richness of the microbial community (p < 0.05), whereas the regular dosing of ferrous salts (0.25 mM) negatively impacted on the EBPR performance. It was found that the abundances of phosphorus accumulating organisms (PAOs) in R2 (micro-dosing) were nearly 1.5-fold and 2-fold higher than those in R1 (control) and R3 (regular dosing). The contributions of biological and chemical pathways towards the observed phosphorus removal were also determined according to the phosphorus releasing rate. For micro-dosage and regular dosage of ferrous salts, phosphorus removal mainly relied on biological phosphorus removal and chemical phosphorus removal, respectively. It appears from this this study that the micro-ferrous dosing strategy is practically feasible and economically viable for enhanced phosphorus removal from municipal wastewater.

Dynamic processes in conjunction with microbial response to disclose the biochar effect on pentachlorophenol degradation under both aerobic and anaerobic conditions

Organochlorines are critical soil contaminants and the use of biochar has recently shown potential to improve soil remediation. However, little is known about biochar-microbe interactions nor the impact on environmental processes such as the immobilization and biodegradation of organochlorine compounds. In this study, we performed microcosm experiments to elucidate how biochar affected the biodegradation and sequestration of pentachlorophenol (PCP). Our results showed that the amendment of biochar markedly inhibited PCP biodegradation due to a strong sorption affinity for PCP under both aerobic and anaerobic conditions. Notably, the inhibitory effect was relatively weaker under anaerobic conditions than under aerobic conditions. The addition of biochar can dramatically shift the bacterial community diversity in the PCP-spiked soils. Under aerobic conditions, biochar significantly stimulated the growth of PCP-degrading bacteria Bacillus and Sphingomonas, but reduced the opportunities for microbes to contact with PCP directly. Under anaerobic conditions, the non-strict organohalide-respiring bacteria Desulfovibrio, Anaeromyxobacter, Geobacter and Desulfomonile were the main drivers of PCP transformation. Our results imply that the use of biochar as a soil remediation strategy for organochlorine compounds should be cautious.

Recent advances in partial denitrification in biological nitrogen removal: From enrichment to application

To maximize energy recovery, carbon capture followed by shortcut nitrogen removal is becoming the most promising route in biological wastewater treatment. As the intermediate of microbial denitrification, nitrite could serve as a substrate for anammox bacteria, while N₂O is a combustion promoter that can increase 37% energy release from CH₄ than O₂. Therefore, the important advances in partial denitrification (PD) that produces nitrite or N₂O as the main product using inorganic or organic electron donors were critically reviewed. Specifically, the enrichment strategies of PD microorganisms were obtained by analyzing the selection pressures, metabolism, physiology, and microbiology of these microorganisms. Furthermore, some prospective and promising processes integrating PD microorganisms and the bottlenecks of current applications were discussed. The obtained knowledge would provide new insights into the upgrading of current WWTPs involving commitment to achieve nitrogen removal from wastewaters more economically and environmentally friendly.

Efficient nitrous oxide recovery from incineration leachate by a nosZ-deficient strain of Pseudomonas aeruginosa

In this study, nitrous oxide was recovered from a lab-scale moving-bed biofilm reactor (MBBR) treating partial nitrification-treated leachate supplemented with a nosZ-deficient strain of Pseudomonas aeruginosa. Batch culture tests with the nosZ-deficient strain determined that the threshold for free nitrous acid (FNA) inhibition was 0.016 mg/L and that FNA concentrations above this threshold severely inhibited denitrification and transcription of genes from the dissimilatory nitrate reduction pathway (narG, nirS, and norB). High nitrite removal and N₂O conversion efficiencies (>95%) were achieved with long-term operation of this MBBR. N₂O accounted for the majority of biogas (80%) produced when the MBBR was fed partial nitrification-treated leachate with high nitrite concentrations and the drainage ratio was adjusted to 30%. Bacterial community analysis revealed that the nosZ-deficient Pseudomonas strain remained metabolically active and was primarily responsible for denitrification processes in the reactor. This study presents a promising method for N₂O recovery from incineration leachate.

Enhanced anaerobic treatment of swine wastewater with exogenous granular sludge: Performance and mechanism

Anaerobic biotechnology has been widely used to the treatment of swine wastewater, but its organic loading rate is far lower than the expected. In this study, the fatigue effect was observed for indigenous anaerobic sludge (IAS) of anaerobic digestion system treating swine wastewater. On the contrary, the enhancement effect was demonstrated for exogenous granular sludge (EGS) originated from the internal circulation reactor treating pulping wastewater. The results showed the anaerobic digestion of swine wastewater with acclimatized EGS was much better than with IAS, 10th-day COD removal efficiency of 85% and 37% respectively. The better performance of acclimatized EGS was attributed to the more efficient degradation of volatile fatty acids (VFAs) as well as a stronger tolerance to the ammonia inhibition of swine wastewater. Revealed by molecular techniques, the acclimatized EGS contained more abundant syntrophic bacteria and methanogens than IAS. These functional microbes colonized in the acclimatized EGS could overcome the fatigue effect of IAS which contained a similar microbial community to pig gastrointestinal tract microbes. This study provides a feasible and promising way to enhance the efficiency of anaerobic digestion of swine wastewater.

Understanding the granulation of partial denitrification sludge for nitrite production

Partial-denitrification (PD) has previously been demonstrated to be another pathway for nitrite production, which provides a cost-effective approach for nitrate (NO₃^--N) removal through combing with anammox. In this study, the formation of PD granules was firstly investigated in a sequencing batch reactor (SBR) with influent nitrate of 60 mg N/L. The granulation process was explored via the physicochemical and biological characterization. Sludge granulation initiated within the first 20 days with an average size of 93.7 μm in diameter, it experienced a developing, shaping and matured periods, with a maximum size of 709.3 μm obtained. High nitrite production of PD was always maintained during the granulation with a mean nitrate-to-nitrite transformation ratio (NTR) of 88.3%, and in-situ maximum NO3-N reduction rate of 84.9 mg N/h/g VSS was obtained. Mature PD granules hold an excellent settling property with 5-min sludge volume index (SVI₅) of 32.0 mL/g MLSS obtained and smooth surface with large amounts of rod bacteria covered. CaCO₃ precipitates formed in the PD process played a vital role in the initial granulation, acting as the nucleus for cell attachment. Extracellular polymeric substances (EPS), mainly the proteins (PN) content, was found to be of supreme importance in granules developing and maintaining its structural stability. Besides, the abundance of Flavobacterium and norank_p__Gracilibacteria were revealed to be in accordance with the change of granules size, seemed to contribute to sludge granulation. The developed granule-based PD integrated with anammox process provides an engineering-feasible and economic-favorable solution for industrial nitrate wastewater treatment.

Deactivation mechanism of calcified anaerobic granule: Space occupation and pore blockage

Calcification and deactivation of high rate sludge bed reactors is a common and serious engineering problem in the application of anaerobic bioreactor. In this study, the characteristics and deactivation mechanism of calcified anaerobic granules were investigated. The results showed that the calcium content of calcified anaerobic granules was ten times higher than that of control anaerobic granules. A large part of the calcium accumulated in the center of anaerobic granules in the form of calcite, and a small part of the calcium distributed in the outer layer of anaerobic granules in the form of Ca-P deposit. The calcium core occupied a large space which was available for the functional microorganisms. The calcium salts deposited in the outer layer of granular sludge which led to the significant reduction of macropore volume. The porosity of calcified anaerobic granules decreased by 13% compared with that of control anaerobic granules, causing generally the decline of methanogenic activity (for example, by 13% at influent organic concentration of 6.6 g COD L^-1). The substrate gradient created by methanation of organic salts, including organic calcium salts, was deduced to be the driving force of anaerobic granule calcification, while the gradual accumulation of calcium salts in anaerobic granules was deduced to be the dominant factor for the decline of anaerobic granule activity.

Towards mainstream deammonification of municipal wastewater: Partial nitrification-anammox versus partial denitrification-anammox

The mainstream deammonification has been believed as a viable technology for the energy-neutral municipal wastewater treatment, which can be realized through two approaches known as partial nitrification-anammox (PN/AMX) and partial denitrification-anammox (PDN/AMX). However, large-scale applications of these deammonification processes for municipal wastewater treatment have been rarely reported thus far. Given such a situation, this review examined the mainstream PN/AMX and PDN/AMX processes with the focus on their engineering feasibility, economic viability and potential challenges. It was revealed that soluble COD and stable nitrite production were the main challenges for mainstream deammonification. Pre-capture of COD was essential for mitigating the competition between denitrifiers and anammox bacteria on nitrite, while NOB suppression and partial denitrification control to nitrite stage were critical issues for stable nitrite production in PN and PDN processes respectively. Compared to nitrification-denitrification, the unit oxygen demand for nitrogen removal in PN/AMX and PDN/AMX could be reduced by 57.3% and 47.7%, while the sludge production could also be cut off by 83.7% and 66.3% in PN/AMX and PDN/AMX respectively. These clearly showed the greater economic viability and environmental sustainability of PN/AMX against PDN/AMX. Consequently, more effort is needed to improve the engineering feasibility of large-scale mainstream deammonification for municipal wastewater treatment.

Characteristics of Microbial Communities and Their Correlation With Environmental Substrates and Sediment Type in the Gas-Bearing Formation of Hangzhou Bay, China

Shallow gas is a kind of natural gas buried in shallow strata, generally, with methane as the main component, endowing it a potential energy resource while also a potential risk to the safety of ground engineering and environment. Microbial activity is usually regarded as an important driving force to generate shallow gas via metabolizing the environmental substrates. Therefore, the research on the microbial communities will be helpful to reveal the distribution of shallow gas in the gas-bearing formation. In this study, 30 sediment samples below the seabed in Hangzhou Bay (China) from depths of 1.5 m to 55 m were collected to investigate their microbial community, environmental characteristics and sediment type (clay or sand). It turned out that the presence of shallow gas had a good correlation with the distribution of archaea rather than bacteria, with the dominant microbe of Bathyarchaeota, Thaumarchaeota, and Euryarchaeota in the formation. Methanosarcinaceae and ANME-1a with the capacity of methane metabolism occupied high proportions. The correlation analysis and redundancy analysis (RDA) suggested that ammonium was a key environmental substrate to indicate the microbial community in the formation. The sediment type was proposed to shape environmental substrates in the formation, thus further affecting the microbial communities. The clay strata were demonstrated to have an important role in the generation and distribution of shallow gas, and more attention should be paid in terms of its resource discovery and engineering safety assessment.

Bacterial community shifts evaluation in the sediments of Puyang River and its nitrogen removal capabilities exploration by resuscitation promoting factor

Identifying indigenous bacterial community and exploring the potential of native microorganisms are crucial for in situ bioremediation of nitrogenous pollutants in water bodies. This study evaluated the bacterial communities of sediment samples from a nitrogen polluted river, and revealed the possible environmental factors shaping the bacterial populations. Importantly, viable but non-culturable bacteria which possessed nitrogen removal capabilities in indigenous population of the sediments were explored by resuscitation promoting factor (Rpf). It was found that the sediments from upstream (URS) and lower stream (LRS) of Puyang river showed both different pollutants levels and bacterial community. Nitrate nitrogen, organic carbon and ammonium nitrogen probably had a significant effect on bacterial compositions between URS and LRS. From URS and LRS, a total of thirteen strains with heterotrophic nitrification ability were resuscitated by Rpf addition, which belonged to genera Bacillus, Pseudomonas, Stenotrophomonas and Acinetobacter. Among them, the strain Pseudomonas sp. SSPR1 was found to display high removal capabilities of simultaneous nitrification and denitrification, and the average ammonium and nitrate removal rates were 2.23 and 0.86 mg/(L·h), respectively. These resuscitated strains could be considered to be used for biological nitrogen removal in rivers and their receiving water bodies.

Integrated upflow anaerobic fixed-bed and single-stage step-feed process for mainstream deammonification: A step further towards sustainable municipal wastewater reclamation

The high energy consumption and excessive waste activated sludge (WAS) production have become the major concerns on the municipal wastewater treatment with conventional biological processes. To tackle these emerging issues, this study demonstrated the feasibility of a novel process integrating an upflow anaerobic fixed-bed reactor (UAFBR) followed by a continuous step-feed reactor for mainstream deammonification towards improved energy efficiency, minimized sludge production and cost-effective ammonium removal. The results showed that 48.8% of the influent chemical oxygen demand (COD) was directly converted to methane gas in UAFBR with minimized sludge production, while 80% of total nitrogen (TN) was removed in the step-feed reactor. Mass balance on the step-feed reactor revealed that the oxic chambers contributed 51.6% of the removed ammonium oxidation to mainly nitrite, while the produced nitrite was immediately removed via anammox with the ammonium supplied by the step-feed in the following anoxic chambers where about 87.1% TN removal occurred. Moreover, it was found that sustainable repression of nitrite oxidizing bacteria (NOB) was achieved without compromising the activity of ammonia oxidizing bacteria (AOB). The anammox bacteria were effectively retained in the anoxic chambers and showed a high specific anammox activity of 0.42 g N/(g VSS·day). These suggest that the step-feed configuration can offer a feasible engineering option towards single-stage mainstream deammonification. It appears that the integrated process developed in this study sheds light on the possible way towards sustainable, energy self-sufficient municipal wastewater reclamation.

Nitric Oxide Dismutase (nod) Genes as a Functional Marker for the Diversity and Phylogeny of Methane-Driven Oxygenic Denitrifiers

Oxygenic denitrification represents a new route in reductive nitrogen turnover which differs from canonical denitrification in how nitric oxide (NO) is transformed into dinitrogen gas. Instead of NO reduction via N₂O to N₂, NO is proposed to be directly disproportionated into N₂ and O₂ in oxygenic denitrification, catalyzed by the putative NO dismutase (Nod). Although a high diversity of nod genes has been recovered from various environments, still little is known about the niche partitioning and ecophysiology of oxygenic denitrifiers. One constraint is that nod as a functional marker for oxygenic denitrifiers is not well established. To address this issue, we compared the diversity and phylogeny of nod, 16S rRNA and pmoA gene sequences of four NC10 enrichments that are capable of methane-driven oxygenic denitrification and one environmental sample. The phylogenies of nod, 16S rRNA and pmoA genes of these cultures were generally congruent. The diversity of NC10 bacteria inferred from different genes was also similar in each sample. A new set of NC10-specific nod primers was developed and used in qPCR. The abundance of NC10 bacteria inferred from nod genes was constantly lower than via 16S rRNA genes, but the difference was within one order of magnitude. These results suggest that nod is a suitable molecular marker for studying the diversity and phylogeny of methane-driven oxygenic denitrifiers, the further investigation of which may be of value to develop enhanced strategies for sustainable nitrogen or methane removal.