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Engineering feasibility, economic viability and environmental sustainability of energy recovery from nitrous oxide in biological wastewater treatment plant
Abstract
Currently, the biological wastewater treatment has been challenged by their high energy consumption. An increasing effort has been devoted to exploring energy recovery from nitrous oxide (N2O) as a powerful fuel additive rather than as an unwanted byproduct during biological nitrogen removal. This review aims to offer a holistic and critical analysis of the ideas for N2O production and energy recovery in terms of engineering feasibility, economic viability and environmental sustainability. It turns out that the recoverable energy from N2O produced in municipal wastewater is below 0.03 kWh/m3, which is insignificant compared with the in-plant energy consumption, while complicated process configuration and high cost associated with harvesting and post-purification of N2O will be incurred. An environmental risk related to global climate change due to the emission of residual dissolved N2O is also concerned. Further effort on N2O production and recovery technologies is indeed required to improve the overall energy balance.
... Recovery of N 2 O is at present a challenging issue that restricts the practical application of energy recovery. It is even more challenging with wastewater having an ammonium concentration of less than 694 mg/L at 25 [87]. Considering 100% N 2 O conversion, the maximum amount of N 2 O generation can be estimated to 35.7 mol/m 3 from a digester reject water with ammonium concentration of 1000 mg/L [32]. ...
... It has been analysed that by using a 100% N 2 O recovery from ammonia, 0.03 kWh/m 3 energy can be recovered, which in practice is significant, as complete conversion to N 2 O cannot be achieved. This recovered energy is insignificant as compared to the energy requirement of these treatment plants [87]. Even allowing co-combustion with CH 4 results in higher energy recovery amounting to around 34% of the energy required during aeration. ...
... Energy recovery from methane is around 13.91 kJ/g COD. Zhang et al. [87] analysed co-combustion of CH 4 from N 2 O in case of municipal wastewater and found only 0.7% of the energy was recovered from COD. Thus, recovery of N 2 O from municipal wastewater with low nitrogen content would not be technologically or economically feasible. ...
... However, according to Zhou et al. (2022) and Scherson et al. (2014), the benefits of increased energy production are negligible and outweighed by the need for adjusted combustion engines, emissions of insufficiently harvested N 2 O, NO x , solubilized N 2 O in effluent and added acetate increasing the carbon footprint, effluent toxicity, depletion of mineral resources and air pollutant emissions. To conclude, CANDO is highly suitable for the treatment of nitrogen-rich reject water, however, according to the literature, known so far, the risks outweigh potential benefits (Zhang et al., 2019). ...
... Vineyard et al. (2021) relied on data for N/D from mainstream, which has a lower N 2 O EF than sidestream treatment (0.9 and 2.1%, respectively) potentially causing an underestimation of emissions (Vasilaki et al., 2019). The emissions of the newly discovered processes such as CANDO or bioelectrochemical systems should also be further investigated, as Zhou et al. (2022) consider only a slightly higher EF for CANDO than for Nit/ Denit without accounting for fugitive emissions of N 2 O purposefully created in the process (Zhang et al., 2019). Similarly, N 2 O production for bioelectrochemical systems remains to be elucidated (Koskue et al., 2022(Koskue et al., , 2010. ...
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.
... In this process, the N 2 O generation efficiency indeed is largely controlled by the intermediates produced through biological reaction (e.g. NO 2 -, NO, HNO 2 and NH 2 OH) as recently reviewed by (Zhang et al., 2019a). At the current technology stage, the environmental sustainability and economic viability to recover N 2 O appears to be debatable due to the challenges associated with harvesting, post-purification of N 2 O as well as the emission of residual dissolved N 2 O (Zhang et al., 2019a), while leading to a complicated process configuration, high operation cost and insignificant recoverable energy against the total in-plant energy consumption. ...
... NO 2 -, NO, HNO 2 and NH 2 OH) as recently reviewed by (Zhang et al., 2019a). At the current technology stage, the environmental sustainability and economic viability to recover N 2 O appears to be debatable due to the challenges associated with harvesting, post-purification of N 2 O as well as the emission of residual dissolved N 2 O (Zhang et al., 2019a), while leading to a complicated process configuration, high operation cost and insignificant recoverable energy against the total in-plant energy consumption. These seem to suggest that a more comprehensive assessment on the N 2 O recovery from municipal wastewater and anaerobic digestion liquor is still needed. ...
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 discussion 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.
... Biological treatment applies the natural capabilities of plants and microbes to degrade, assimilate or transform the pollutants to render them nontoxic to the surrounding ecosystem [8]. Biological treatment is considered as a cost-effective and eco-friendly approach to eliminate pollutants without negatively impacting the surrounding environment [9][10][11][12]. There are several studies recorded to date, for instance the study by Ayed et al. [13] who utilised aerobic and anaerobic bacterial species for efficient removal of reactive blue dye from real textile effluent without impacting environment. ...
The prediction of pollutants removal efficiency from the generated effluent of a treatment plant is valuable and can reduce the time, sampling and energy required during performance assessment. The present study aims to predict the effect of different input parameters on the treatment efficiency of the developed microbial‐based anaerobic process for textile effluent using machine leaning algorithms. The decolourisation and chemical oxygen demand (COD) reduction of the treated effluent were predicted on the basis of the three different input parameters pH, COD and colour value of the textile wastewater. The effectiveness of different machine learning algorithms, support vector machines (SVM), random forest (RF), gradient boost regressor (GBR), AdaBoost, extreme gradient boosting (XGB) regressor and voting regressor, were evaluated based on the correlation coefficient ( R ² ) value. The results revealed that the RF achieved the highest accuracy for decolourisation (training data R ² : ∼0.85 and test data R ² : ∼0.84) as well as COD reduction (training data R ² : ∼0.87 and test data R ² : ∼0.94) compared to the other algorithms. These results were validated experimentally, confirming that RF can be used as a tool to predict the performance efficiency of a microbial‐based treatment system.
... In the recent times, biological wastewater treatment methods (e.g. for treating municipal wastewater, sulphate, heavy metals, pharmaceuticals) have garnered significant attention over physico-chemical methods due to their cost-effective and environment friendly nature [12][13][14]. Fungi (e.g. for selenite removal) have been widely used in bioreactors (Table 1) for their ability to break down pollutants and withstand unfavorable conditions such as low pH, high pollutant concentrations, and inadequate nutrition availability [15]. The potential of sulphate reducing bacteria (SRB) was explored in a packed bed reactor (PBR) for sulphate removal from wastewater using CO as a carbon source [16]. ...
... To remove nutrients from wastewater, several chemical treatments and conventional physical methods are used. However, high cost, excessive generation of greenhouse gases (GHGs), and more sludge production are the major disadvantages limiting their use (Zhang et al., 2019). Moreover, through physical and chemical processes, contaminants and pollutants in wastewater are not fully removed from wastewater. ...
Huge discharge of different organic and inorganic waste compounds into water sources is the prime reason for water pollution. To protect the environment, appropriate biological treatment methods of wastewater with high removal efficacy are needed. To meet this end, indigenously available microbial consortiums were explored for their possible bioremediation efficiency. Cyanobacteria purified from microbial consortium was identified as Desertifilum sp. based on 16 s rRNA gene sequencing, and its biochemical characteristics were determined. High-rate algal pond (HRAP) of 6 m³ volume with dimensions of 3 m × 2 m × 1 m was inoculated @ 0.25% and operated in an open environment at a light intensity of 38,000 to 62,000 lx with a hydraulic retention time (HRT) of 12 days. Results obtained after 12 days showed removal efficiencies of 78.26, 76, 79.55, 4.77, and 58.74% for soluble chemical oxygen demand (sCOD), total chemical oxygen demand (tCOD), biochemical oxygen demand (BOD), nitrates, and total phosphorus, respectively. The results from the study inferred that Desertifilum sp. is a suitable candidate for secondary-stage wastewater treatment without any additional amendment. Moreover, the biochemical composition of the biomass obtained unraveled its potential application in the field of nutraceuticals.
... Several empirical investigations use single environmental indicators to measure the state of the environment on a national or international basis. Researchers have previously employed a variety of environmental proxies, including emissions of sulfur dioxide (SO 2 ) (Selden and Song, 1994), nitrous oxide (N 2 O) (Janke et al., 2009;Zhang et al., 2019) and particulate matter (PM 2.5) (Ouyang et al., 2019). Carbon dioxide (CO 2 ) emissions, however, are the most pertinent and widely used environmental indicator (Ikram et al., 2020;de Souza Mendonça et al., 2020). ...
Purpose
The present study aims to construct and compare Composite Environmental Sustainability Index (CESI) for 20 emerging countries for the period 1990–2020.
Design/methodology/approach
The study constructs CESI using the principal component analysis (PCA). Furthermore, for the preparation of index weights, varimax rotation is used to get component loadings.
Findings
The study finds that the overall CESI values lies between 2 and 4.8 for the 20 emerging countries considered in the study. This study depicts a diverse picture of environmental sustainability among emerging countries. The study also shows the trend of CESI values from 1990 to 2020. The bottom three countries whose CESI is very low compared to others are Iran, South Africa and Saudi Arabia. However, Brazil, Columbia and Chile are top three highest scorers in 2020.
Originality/value
The study contributes to the literature by constructing a composite index comprising of three sub-indices to measure the environmental sustainability of an economy. These sub-indices include seven indicators that are more inclusive and comprehensive. To the authors' knowledge, this is a pioneering attempt in the construction of the index for emerging countries.
... When the wastewater quality and quantity fluctuate, the operation accuracy and hysteresis problem are serious. The management process of WWTPs is not highly refined, and the stability of wastewater treatment effect needs to be improved [4,5]. Meanwhile, in order to meet the needs of sustainable development strategy of social economy, the requirements of effluent quality of WWTPs are more stringent [6]. ...
The management of traditional wastewater treatment plants(WWTPs) mostly rely on human experience, resulting in high cost and low efficiency under conservative operation mode. This study proposed an online intelligent management method based on plan library to improve the wastewater treatment performance. The operation plans in plan library were obtained based on the mechanism model (Activated Sludge Models) of a pilot Anaerobic-Anoxic-Oxic (A 2 /O) process, and each plan represents the optimal operation strategy under a specific influent condition. Then the plan library was input to train a data driven model, i.e. a Multi-Layer Perceptron (MLP) regression model. The trained MLP model can be used to generate more detailed online operation strategies for wastewater treatment process under different influent conditions. After a 124 days continuous operation of the A 2 /O process, the results shown, the proposed method can generate online operation strategies according to influent conditions, and the main effluent indicators meet the discharge standards continuously and stably. Meanwhile, compared with the manual operation mode, the aeration energy consumption was saved about 49.4 % by using the proposed method. The mechanism model and data-driven model were combined in this study, and it has scientific value and engineering significance for intelligent management of WWTPs.
... With the development of sewage treatment Environmental Science and Pollution Research technology, researchers are committed to exploring the recovery of energy from N 2 O rather than the unnecessary by-products in the process of biological denitrification. Zhang et al. (2019) believed that the recoverable energy of N 2 O in urban sewage is less than 0.03 kWh/m 3 , which is not only difficult to support the consumption of STPs but also produces extremely high costs of the complex collection and processing process. Therefore, the N 2 O recovery and utilization technology of the STPs still need further breakthroughs. ...
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.
... Traditional technologies for biogas slurry treatment include membrane separation, flocculation, advanced oxidation, activated sludge process, etc. They are either inefficient, expensive, easy to be blocked, high energy consumption, poor in nitrogen and phosphorus removal (Feng et al., 2020;Zhang et al., 2019), or easy to cause secondary pollution and release large amounts of greenhouse gases (Shinde et al., 2021). Microalgae can grow by using nitrogen, phosphorus, and some organic matter in biogas slurry as nutrients (Shuba & Kifle, 2018;Yong et al., 2021). ...
... The key mechanism in CAS is the introduction of a huge amount of air for oxidation to meet the chemical oxygen demand (COD) and the high energy consumption of the nitrogen removal processes. During operation, a substantial fraction of COD is lost as metabolic heat through aerobic respiration, thereby reducing energy recovery potential in subsequent anaerobic sludge digestion, and the energy-intensive nature of biological nutrient removal (BNR) also has a major effect on the operational budgets of CAS plants (Zhang et al., 2019). Finally, conventional nitrogen removal processes require long solids retention times (SRTs) which increases the size of installations (Jetten et al., 1997;Zhou et al., 2021). ...
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.
... For many companies, the concepts of growth and development are now examined collectively when discussing sustainability. The importance of sustainability is clear, especially in the energy sector, where environmental pollution has proven that energy investments need to be sustainable, and clean energy production must be realized (Zhang et al., 2019). With the power of social networks, current environmental pollution issues are often shared on social networks, often disclosing the energy companies that cause environmental pollution. ...
Purpose:
Companies must implement sustainability measures in order to survive due to the relationship between financial, social and environmental performances. These elements must be integrated into the business in a complementary manner in this regard. As a result, this study aims to investigate the effects of entrepreneurial leadership on sustainability, as well as financial and process innovation.
Design/methodology/approach:
Within the scope of the research, a survey was conducted with 295 white-collar employees working in energy companies. SPSS 25, the LISREL program, and SOBEL analysis were used to determine the relationships between the variables.
Findings:
In the research, financial innovation perceptions and process innovation activities have a positive effect on business sustainability and entrepreneurial leadership. As both an independent and a mediating variable, entrepreneurial leadership has a positive impact on business sustainability.
Research limitations/implications:
Companies engaged in renewable energy production, operating in the Marmara region, constitute the sample mass. For this reason, it would be more accurate to evaluate the results obtained in this research only for companies producing renewable energy.
Practical implications:
It is concluded that energy companies should prioritize financial and process innovations and that entrepreneurial leadership is required to ensure the sector's long-term viability.
Originality/value:
This paper is an innovative study in terms of the scope and content of the research as data are collected and analyzed from companies that produce renewable energy.
... Most trials reported in literature on N 2 O recovery are still in labscale, while to expand them to industrial scale acquires excess research efforts. The high solubility and low concentration of N 2 O in wastewater would incur high separation and purification costs, as well as intricate plant setup needed, to achieve the purity required for commercial use (Zhang et al., 2019). In addition to the issues addressed in Section 3.7, whether the removal of N 2 O would affect the performances of other pollutants removal is an important topic for further investigation. ...
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.
... Traditional technologies for biogas slurry treatment include membrane separation, flocculation, advanced oxidation, activated sludge process, etc. They are either inefficient, expensive, easy to be blocked, high energy consumption, poor in nitrogen and phosphorus removal (Feng et al., 2020;Zhang et al., 2019), or easy to cause secondary pollution and release large amounts of greenhouse gases (Shinde et al., 2021). Microalgae can grow by using nitrogen, phosphorus, and some organic matter in biogas slurry as nutrients (Shuba & Kifle, 2018;Yong et al., 2021). ...
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.
... Therefore, treatment of these wastewaters is essential before their disposal into water reservoirs to meet the discharge regulations as well. So far, numerous approaches have been used for wastewater treatment, such as coagulation [7,8], adsorption [9,10], electrocoagulation [11], photocatalysis [12,13], etc. Similarity, the biological wastewater treatment (BWT) is one of the most frequent and essential treatment techniques for municipal and industrial wastewaters [14,15]. It can remove different contaminants and oxidize a variety of organic molecules, turning them into stable chemicals and biomass that can be isolated from water [16,17]. ...
This research explores the feasibility of using an algal photo-bioreactor as an integrated algal-bacterial treatment system combined with a dissolved air flotation (DAF) system for the deduction of COD, BOD 5 , TSS, TN and TP from primary treated wastewater (PTW). Isolated algae species of Anomoeoneis, Scenedesmus, Anabaena and Spirulina at fixed hydraulic retention time (HRT) of 16 h were used to conduct batch experiments to determine optimum conditions of pH, temperature, light intensity and mixing rate on the removal rates of contaminants. The optimum removal rates were studied at neutral pH, 25 • C, light intensity of 90 μmol m − 2 S − 1 and 100 rpm mixing rate. A scaled-up pilot plant treatment system was designed, constructed and operated to evaluate the system performance to treat (0.1 L/min) of primary treated wastewater disposed of ZENIN WWTP-Giza, Egypt. The design criteria of the algal photo-bioreactor were acquired from the batch investigations. The plant was operated for 10 continuous days and the analytical analysis was performed twice a day at a fixed time. The DAF system was used to isolate the infiltrated algae from the system for cultivation and reuse purposes. The achieved results revealed the superior COD, BOD 5 , TSS, TN and TP removal percent reached in average 56.4%, 61%, 59.2%, 48.3% and 51.7% at 12 pm and 49.7%, 54.9%, 52.4%, 39% and 40.57% at 12 am, respectively. All data gained from experimental studies demonstrated the efficiency of using algal photo-bioreactor combined with DAF system as an effective wastewater treatment technique.
... A review of research (presented in Table 1) has been conducted in various fields of studies (clusters) from the perspective of the aspects analyzed in this paper, such as: Industry 4.0, Sustainability, and Energy 4.0. [38,[44][45][46][47] Analysis of problematic Industry 4.0 in relation to management and IT operations; [48][49][50] Role of Industry 4.0 in transportation research; [51,52] Analysis of social environment from the Industry 4.0 perspective; [53] Sustainability Analysis of energy efficiency trends in the context of sustainability; [54][55][56][57] Focus on sustainable economic development; [58] Research conducted in the field of sustainable manufacturing; [59,60] Energy 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.
... leaks from nylon manufacture in newly industrialized countries). However, although it may be possible to reduce emissions from wastewater [138] the feasibility of the task may be limited by the cost in energy and effort [139]. A minor source, that may be amenable to control either by taxation or regulation, is from whipped cream chargers and their misuse in small steel cylinders for so-called legal highs. ...
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 ¹³ C, 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)'.
... In addition, the treatment costs of excess sludge can account for 25%-65% of the operational costs of WWTPs (Zhang et al., 2019c). Therefore, in view of the current energy depletion and serious environmental pollution conditions, the conventional nitrogen removal process is bound to become a major barrier that hinders the sustainable environmental development (Zhang et al., 2019b), whereas autotrophic nitrogen removal processes, such as anammox, are a feasible alternative technology (Jo et al., 2020). Simultaneous partial nitritation, anammox, and denitrification (SNAD) process, which is considered a promising technology (Guo et al., 2020), can break through the theoretical maximum nitrogen removal efficiency of 89% in the partial nitrification-anammox (PN/A) process and reach 100% complete nitrogen removal (Figueroa et al., 2012). ...
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.
... On this way 70e90% of antibiotics will be excreted intact or in metabolites by faeces and urine (Mass e et al., 2014). Another persistent problem in swine wastewater is related to the amount of nutrients such as nitrogen and phosphorous (Zhang et al., 2019). Part of these nutrients and antibiotics are not processed by pigs and can reach the farmlands due to the conventional application of the swine wastewater (Joshi and Wang, 2018). ...
The increase on pork meat demand is consequently leading to higher production of swine wastewater. These wastewaters are problematic due to their high organic matter load and nutrients content that can promote soil and aquatic sources contamination. The conventional effluents treatment technologies seem to be inefficient for total organic matter and contaminants removal while demanding high retention times. One of the steps considered for the swine wastewater treatment is solid-liquid separation. In this work, coagulation using polyDADMAC was evaluated and the effect of the coagulant concentration for this purpose was tested. This methodology was compared with an innovative approach involving biofiltration through the invasive bivalve Corbicula fluminea. The effects of the liquid to clam’s ratio was assessed as well as the mechanism of organic matter removal and the clams reuse capacity. The best chemical oxygen demand (COD) removal obtained was 51 % using 1 L of effluent per 150 clams. Moreover, it was possible to reuse the clams during 4 cycles without losing significant efficiency on the COD removal. Moreover, the toxicity of the treated wastewater was evaluated regarding Aliivibrio fischeri and Lepidium sativum. Aeration without clams reduced the toxicity levels. However, for Lepidium sativum germination index the best result was obtained for the wastewater treated by clams. Thus, C. fluminea presents potential for swine wastewater treatment.
... On this way 70e90% of antibiotics will be excreted intact or in metabolites by faeces and urine (Mass e et al., 2014). Another persistent problem in swine wastewater is related to the amount of nutrients such as nitrogen and phosphorous (Zhang et al., 2019). Part of these nutrients and antibiotics are not processed by pigs and can reach the farmlands due to the conventional application of the swine wastewater (Joshi and Wang, 2018). ...
In this work, Fenton’s process was evaluated as an alternative treatment of swine effluent. In order to improve depuration, coagulation and biofiltration were integrated with Fenton’s peroxidation. With the optimum loads of 750 mg/L of hydrogen peroxide and iron, this process was able to remove 72 % of sCOD and lowering Aliivibrio fischeri luminescence inhibition to 65 %. On the other hand, integration between Fenton’s process and biofiltration removed 91 % of sCOD. Whereas, after coagulation sCOD degradation reaches 86 %. Regarding to luminescence inhibition, the treatment processes integration can decrease it to about 30 %. Coagulation and biofiltration after Fenton’s process proved to be able to remove dissolved iron in the treated effluent and thus overcoming Fenton’s process major disadvantage.
... In addition, the treatment costs of excess sludge can account for 25%-65% of the operational costs of WWTPs (Zhang et al., 2019c). Therefore, in view of the current energy depletion and serious environmental pollution conditions, the conventional nitrogen removal process is bound to become a major barrier that hinders the sustainable environmental development (Zhang et al., 2019b), whereas autotrophic nitrogen removal processes, such as anammox, are a feasible alternative technology (Jo et al., 2020). Simultaneous partial nitritation, anammox, and denitrification (SNAD) process, which is considered a promising technology (Guo et al., 2020), can break through the theoretical maximum nitrogen removal efficiency of 89% in the partial nitrification-anammox (PN/A) process and reach 100% complete nitrogen removal (Figueroa et al., 2012). ...
A method is reported based on a novel adsorbent for the determination of five phenols in river water by on-line solid-phase extraction (SPE) coupled with high-performance liquid chromatography. Acryloyl-β-cyclodextrin and N-isopropylacrylamide were grafted to the silica surface to prepare the adsorbent that was placed in a laboratory-constructed double-pass screw column (10 mm × 2 mm, i.d.) for on-line SPE. In addition, to obtain the optimum on-line SPE conditions, the sampling flow rate, sample volume, eluent flow rate and time, and methanol ratio in the eluent were investigated. Under the optimal experimental conditions, the response of the method was linear for phenol concentrations from 0.1 to 500.0 ng mL⁻¹. The limits of detection were between 0.080 and 0.72 ng mL⁻¹ and the limits of quantification from 0.27 to 2.4 ng mL⁻¹. The intra-day and inter-day relative standard deviations were from 1.1% to 4.9% (n = 3) and 1.5% to 5.7% (n = 3), respectively. The spiked recoveries of the river water samples were from 87.5% to 111%. This adsorbent was suitable for the preconcentration of trace phenols from aqueous solution. The established method was simple, time-saving, automated, and cost-effective.
Instead of the conventional perception of nitrous oxide (N2O) as a potent greenhouse gas whose production should be minimized, this work aimed to assess N2O recovery as a potential energy source from nitric oxide (NO) in the form of Fe(II)EDTA-NO through element sulfur (S⁰) or thiosulfate (S2O3²⁻)-driven NO-based autotrophic denitrification (SNADS0 or SNADS2O3). A mathematical model was proposed to describe substrate dynamics related to N2O production and reduction and was successfully calibrated and validated using batch experimental data from lab-scale SNADS0 and SNADS2O3 systems under different substrates conditions. The model was subsequently employed to assess the potential of N2O accumulation and recovery by altering the S/N mass ratio and the ratio of gas volume to liquid volume of the system. The simulation results suggested that with a S/N mass ratio of nearly 1.0, high-purity N2O could be more rapidly and efficiently recovered from Fe(II)EDTA-NO in the SNADS0 and SNADS2O3 systems with a higher ratio of gas volume to liquid volume (i.e., a N2O recovery efficiency of up to 80.2%−84.9% reached within 3.1 h−3.5 h under the studied conditions). Comparatively, the SNADS0 process showed an economic and viable advantage for practical applications to the efficient treatment and resource utilization of NO-containing flue gas.
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 shown that ammonium recovery is a game-changer towards the sustainable municipal wastewater reclamation. Meanwhile, the novel processes with enhanced energy and resource recovery are also discussed, which offer useful insights into the ways to achieve the carbon-neutral municipal wastewater reclamation.
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.
The application of biological process for the high saline mariculture wastewater treatment was hindered primarily by salinity and settleability. Photogranule is an effective wastewater treatment technology with excellent settleability and resistance to environmental changes. In this study, internal circulating photogranular membrane bioreactor (IC-PMBR) and internal circulating photogranular sequencing batch bioreactor (IC-PSBR) were constructed to cultivated photogranules. The result showed that mature photogranules quickly formed within one month for both photobioreactors. IC-PMBR exhibited more excellent pollutants removal performance than IC-PSBR. The removal efficiencies of TN, PO4³⁻ and TOC in IC-PMBR were 95 ± 3%, 78 ± 6% and 85 ± 3%, respectively. The excellent nitrogen removal in both bioreactors was ascribed to the enrichment of Proteobacteria and Cyanobacteria. Interestingly, the increasing abundance of Leucothrix could enhance the denitrification in the IC-PMBR. The removal of phosphate was achieved by phosphate accumulating organisms (PAOs) (mainly Thiothrix) and cyanobacteria in the IC-PMBR, while only p-accumulation microalgae dominated the phosphate intake in the IC-PSBR. Moreover, the synergy of heterotrophic bacterial and microalgae improved the removal efficiency of organics in both bioreactors. Morphology observation and community analysis revealed that the key players in photogranules from IC-PMBR was Phormidium sp. acting as backbones and interweaving a mat on the surface of granules. In contrast, an integrated Leptolyngbya sp. with false branching was observed in photogranules from the IC-PSBR acting as an interior core and mat-like structure was absent. Noticeably, an anaerobic region was detected in photogranules from both bioreactors with different proportion, primary Rhodobacteraceae and Thiotrichaceae. Therefore, this study demonstrated that cultivating photogranules in continuous-flow membrane photobioreactor provided an alternative option for high saline wastewater treatment.
Partial-denitrification (PD, NO3⁻-N→NO2⁻-N) is emerging as a promising approach for application of anaerobic ammonium oxidation (an) 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 (rno3) 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.
Constructed wetlands (CWs) can remove nitrogen (N) through plant assimilation and microbial nitrification and denitrification, while it also releases large greenhouse gas nitrous oxide (N2O) into the atmosphere. However, N2O emissions and the underlying microbial mechanisms of CWs when treating high-strength wastewater have not been systematically surveyed. Here, the effect of three influent strengths on N2O emissions in a pilot-scale CW treatment of swine wastewater was determined and the underlying microbial mechanisms were explored. The results showed that the removal rates of ammonium (NH4⁺) and total nitrogen (TN) increased significantly with the increasing influent strengths, however, the ratio of N2O emission/TN removal rose by 1.5 times at the same time. Quantitation of microorganisms responsible for N-cycle in the sediment indicated that the abundance of ammonia-oxidizing bacteria (AOB) in high influent strengths (COD, 962.38 ± 3.05 mg/L; NH4⁺, 317.89 ± 4.24 mg/L) was 51.6-fold compared with that in low influent strengths (COD, 516.94 ± 4.18 mg/L; NH4⁺, 100.65 ± 2.65), and AOB gradually replaced ammonia-oxidizing archaea (AOA) to dominate ammonia oxidizers. Structural equation models demonstrated that NO2⁻ accumulations promoted the ratio of AOB/AOA, which further led to an increase in the ratio of N2O emission/TN removal. It is worth notice both the N removal rates and N2O emissions increased with the increasing influent strength. To obtain reduced N2O emissions, pretreatment technology for strength reduction should be supplemented before high-strength wastewater enters the CWs. This study may shed new light on the sustainable operation and application of CWs.
Water pollution being a global issue is getting worse day by day. Direct disposal of wastewater containing organic and inorganic, dissolved and suspended pollutants may pose serious threats to the terrestrial and aquatic life, thus disturbing the natural ecosystem. Therefore, the treatment of such hazardous wastewater is of utmost necessity. In this context, several physicochemical and biological treatment technologies of wastewater are in progress worldwide. However, some of these conventional wastewater treatment technologies proved to be expensive, time-consuming with maximum manpower and infrastructure requirement with minimum treatment efficiency. Nanotechnology appears as an emergent and diverse field for the effective removal of contaminants from wastewater. Nanomaterials are excellent adsorbents and catalysts due to their larger specific surface areas and high reactive nature. Moreover, the flexibility of nanomaterials in solution is high and even a small number of nanomaterials is enough to degrade pollutants present in wastewater. Nanoparticles can be synthesized through chemical and biological routes. However, among biological methods, “green synthesis/phytogenic-mediated synthesis of nanoparticles” using plants and plant products is an efficient, cost-effective, safe, and environment-friendly approach that does not have high pressure, temperature, and energy requirements as well as does not produce toxic substances. Besides, a huge variety of plants are easily accessible to produce nanoparticles on a large scale
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.
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.
Maximizing production and use of N2O produced by the process of denitrification has emerged as a promising concept for energy recovery from nitrogen. Acetylene is well known as an inhibitor of N2O reductase activity, however, to date, few studies have utilized long-term cultivation with acetylene to achieve denitrifying N2O recovery. This work assessed the performance of N2O production and shifts in the denitrifying community in response to long-term exposure of acetylene during nitrite denitrification. Batch tests showed that long-term exposure to acetylene at high concentrations (volume fraction >40 %) resulted in high N2O accumulation, up to 98.6 %. High-throughput 16S rRNA gene analysis suggested that Saprospiraceae dominated the microbial community at the end of the cultivation period with its abundance increasing from the initial 3.2% to 42.2%. Metagenomic analysis revealed that after the long-term cultivation under high level acetylene, the relative abundance of nosZ in the community did not change significantly. Instead, the nosZⅡ-harboring bacteria became dominant. Batch tests in series demonstrated that N2O reduction could be restored rapidly upon removal of acetylene. This study describes an effective method for high yield production of N2O during nitrite denitrification that can be used to enhance energy recovery and improves our understanding of the long-term effect of acetylene on the denitrifying community.
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.
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.
Immobilization is a method to enhance the activity, the stability and the reusability of enzymes. This study aims to evaluate the capacity of laccase from Trametes hirsuta EDN 082 immobilized in the activated Light Expanded Clay Aggregate (LECA) for dye decolorization. The effects of enzyme loading, the dosage of immobilized laccase-LECA, and the enzyme reusability were investigated. The results showed that the immobilization yield laccase-LECA was 78.78%. One gram of immobilized laccase-LECA with 4.65 U/g of enzyme loading decolorized 99.29% Remazol Brilliant Blue R (RBBR) dye for 3 h. The immobilized laccase-LECA reusability was up to 6 number cycles with 79.67% of the remaining decolorization rate. Immobilized laccase also shifted wide pH and temperature values compare to free enzyme. The kinetic study showed that the specific decolorization rate increases with an increase in initial dye concentration up to 700 and 900 mg/L for laccase-LECA and free laccase, respectively.
Nitrous oxide (N 2 O) has been studied intensively in 6 wastewater treatment as a detrimental greenhouse gas. However, 7 increasingly more studies have adopted a contrasting objective, 8 recovering N 2 O from wastewater as an energy resource. This article 9 critically reviewed and analyzed the current status of N 2 O recovery 10 research in wastewater treatment, to identify knowledge gaps and 11 guide future research. Overall, N 2 O recovery is a promising 12 research direction while still in active development. At present, 13 unstable nitritation, the low energy potential, and potential 14 environmental risks of N 2 O harvesting render the recovery of 15 N 2 O from mainstream wastewater technically and economically challenging. High-strength wastewater treatment is more favorable 16 for N 2 O recovery due to the high energy potential, established nitritation approaches, and significant carbon/aeration savings. The 17 coupled aerobic−anoxic nitrous decomposition operation (CANDO) process is currently the most investigated and promising N 2 O 18 recovery process. Nevertheless, more research is needed for its implementation on a large scale. Research opportunities for the 19 CANDO process have been identified in this paper. Meanwhile, N 2 O recovery via autotrophic denitritation is a more recent concept, 20 with limited studies hitherto. More experiments are needed to investigate its technological feasibility. Furthermore, other novel N 2 O 21 recovery processes, e.g., truncated denitrification and chemical oxidation, should also be explored to facilitate the recovery of N 2 O 22 from wastewater.
We evaluated the feasibility of waste-generated heat using a 100-kW digestion gas engine at the Karatsu City Water Purification Center by evaluating its disaster resilience through four indicators. We achieved the best outcome, i.e., a power generation rate of 1,122 kW and a power self-sufficiency rate of 22% when two or more digestion gas engines were installed to supply waste-generated heat to the absorption chiller/heater of a water-pool. Additionally, we evaluated the environmental and economic aspects of a Mechanical Biological Treatment (MBT) system installed in Karatsu City. The results suggested that by installing an MBT system, the annual cost could be reduced by ∼100 million Yen and the power generation capacity could be increased to 4,310 kW; this could also help reduce 19,000 tons of annual CO 2 emissions with increased power generation. The environmental and economic feasibility assessment tool developed here is configurable; hence, applicable to other regions.
Nitrous oxide (N2O) is formed during wastewater nitrogen removal processes. It is a strong greenhouse gas, however, if properly captured it can also be used as a renewable energy source. In this study, a nosZ-deficient strain of Pseudomonas aeruginosa was constructed. During growth under denitrifying conditions, the nosZ-deficient strain was more highly transcribing other genes from the denitrification pathway (narG, nirS, and norB) than the wild-type strain. This strain could also convert 85% of NO2--N to N2O when it was grown with acetate compared to <0.6% by the wild-type strain. When a bioreactor treating synthetic wastewater with high NO2--N concentrations (700 mg/L) was inoculated with this strain, the N2O conversion efficiencies were >73% and N2O comprised 73~81% of the biogas being generated. The energy yield from wastewater in bioaugmented reactors also reached levels as high as 1260 kJ/m3. These results are significant and show that bioaugmentation of reactors during denitrification treatment processes with nosZ-deficient strains of Pseudomonas or other core denitrifying bacteria might be an effective way to enhance N2O recovery.
International climate change agreements typically specify global warming thresholds as policy targets¹, but the relative economic benefits of achieving these temperature targets remain poorly understood2,3. Uncertainties include the spatial pattern of temperature change, how global and regional economic output will respond to these changes in temperature, and the willingness of societies to trade present for future consumption. Here we combine historical evidence⁴ with national-level climate⁵ and socioeconomic⁶ projections to quantify the economic damages associated with the United Nations (UN) targets of 1.5°C and 2°C global warming, and those associated with current UN national-level mitigation commitments (which together approach 3°C warming⁷). We find that by the end of this century, there is a more than 75% chance that limiting warming to 1.5°C would reduce economic damages relative to 2°C, and a more than 60% chance that the accumulated global benefits will exceed US$20 trillion under a 3% discount rate (2010 US dollars). We also estimate that 71% of countries - representing 90% of the global population - have a more than 75% chance of experiencing reduced economic damages at 1.5°C, with poorer countries benefiting most. Our results could understate the benefits of limiting warming to 1.5°C if unprecedented extreme outcomes, such as large-scale sea level rise⁸, occur for warming of 2°C but not for warming of 1.5°C. Inclusion of other unquantified sources of uncertainty, such as uncertainty in secular growth rates beyond that contained in existing socioeconomic scenarios, could also result in less precise impact estimates. We find considerably greater reductions in global economic output beyond 2°C. Relative to a world that did not warm beyond 2000-2010 levels, we project 15%-25% reductions in per capita output by 2100 for the 2.5-3°C of global warming implied by current national commitments⁷, and reductions of more than 30% for 4°C warming. Our results therefore suggest that achieving the 1.5°C target is likely to reduce aggregate damages and lessen global inequality, and that failing to meet the 2°C target is likely to increase economic damages substantially.
Potable water reuse applications can provide a safe and sustainable water supply where conventional freshwater resources are limited. The objectives of this study were fourfold: (i) to analyze existing potable water reuse applications regarding operational characteristics and energy demands, (ii) to determine the theoretical energy potential of wastewater and identify opportunities for energy recovery, (iii) to define design requirements for potable water reuse schemes that integrate energy recovery, (iv) to propose strategies for more energy efficient potable water reuse schemes. Existing potable water reuse schemes commonly utilize conventional wastewater treatment processes including biological nutrient removal followed by advanced water treatment processes. While meeting a high product water quality, these treatment schemes are characterized by relatively high specific energy demands (1.18 kWh/m³). Given that the theoretical energy potential of municipal wastewater is approximately 2 times higher (2.52 kWh/m³), opportunities exist to integrate energy recovery strategies. We propose three alternative potable water reuse schemes that integrate energy recovery from carbon via methane and nitrogen via either the coupled aerobic-anoxic nitrous decomposition operation process or partial nitritation/anammox. Compared to conventional potable water reuse schemes, the energy requirements of these schemes can be reduced by 7–29%, the overall energy balance by 38–80%.
Driven by energy neutral/positive of wastewater treatment plants, significant efforts have been made on the research and development of mainstream partial nitritation and anaerobic ammonium oxidation (anammox) (PN/A) (deammonification) process since the early 2010s. To date, feasibility of mainstream PN/A process has been demonstrated and proven by experimental results at various scales although with the low loading rates and elevated nitrogen concentration in the effluent at low temperatures (15-10 °C). This review paper provides an overview of the current state of research and development of mainstream PN/A process and critically analyzes the bottlenecks for its full-scale application. The paper discusses the following: (i) the current status of research and development of mainstream PN/A process; (ii) the interactions among aerobic ammonium-oxidizing bacteria, aerobic nitrite-oxidizing bacteria, anammox bacteria, and heterotrophic bacteria; (iii) the suppression of aerobic nitrite-oxidizing bacteria; (iv) process and bioreactors; and (v) suggested further studies including efficient and robust carbon concentrating pretreatment, deepening of understanding competition between autotrophic nitrogen-converting organisms, intensification of biofilm anammox activity, reactor design, and final polishing.
Herein, results of combined greenhouse gas treatment with clean energy conversion is reported for the first time. Multi-channel tubular SOFCs were operated with N2O instead of air as the oxidant leading to a 50% increase in power density. Techno-economic evaluation suggested the feasibility of the combined approach eliminating the cost penalty for N2O abatement.
Although the activated sludge process, one of the most remarkable engineering inventions in the 20 th century, has made significant contribution to wastewater reclamation in the past 100 years, its high energy consumption is posing a serious impact and challenge on the current wastewater industry worldwide and is also inevitably linked to the issue of global climate change. In this study, we argued that substantial improvement in the energy efficiency might be no longer achievable through further optimization of the activated sludge process. Instead, we should devote more effort to the development or the adoption of novel treatment configurations and emerging technologies. Of which an example is A-B process which can significantly improve the energy recovery potential at A-stage, while markedly reduces energy consumption at B-stage. Various configurations of A-B process with energy analysis are thus discussed. It appears highly possible to achieve an overall energy gain in WWTPs with A-B process as a core.
Hollow fibre membrane contactor (HFMC) systems have been studied for the desorption of dissolved methane from both analogue and real anaerobic effluents to ascertain process boundary conditions for separation. When using analogue effluents to establish baseline conditions, up to 98.9% methane removal was demonstrated. Elevated organic concentrations have been previously shown to promote micropore wetting. Consequently, for anaerobic effluent from an upflow anaerobic sludge blanket reactor, which was characterised by a high organic concentration, a nonporous HFMC was selected. Interestingly, mass transfer data from real effluent exceeded that produced with the analogue effluent and was ostensibly due to methane supersaturation of the anaerobic effluent which increased the concentration gradient yielding enhanced mass transfer. However, at high liquid velocities a palpable decline in removal efficiency was noted for the nonporous HFMC which was ascribed to the low permeability of the nonporous polymer provoking membrane controlled mass transfer. For anaerobic effluent from an anaerobic membrane bioreactor (MBR), a microporous HFMC was used as the permeate comprised only a low organic solute concentration. Mass transfer data compared similarly to that of an analogue which suggests that the low organic concentration in anaerobic MBR permeate does not promote pore wetting in microporous HFMC. Importantly, scale-up modelling of the mass transfer data evidenced that whilst dissolved methane is in dilute form, the revenue generated from the recovered methane is sufficient to offset operational and investment costs of a single stage recovery process, however, the economic return is diminished if discharge is to a closed conduit as this requires a multi-stage array to achieve the required dissolved methane consent of 0.14mgl-1.
Partial nitrification has gained broad interests in the biological nitrogen removal (BNR) from wastewater, since it alleviates carbon limitation issues and acts as a shortcut nitrogen removal system combined with anaerobic ammonium oxidation (Anammox) process. The occurrence and maintenance of partial nitrification relies on various conditions, which favor ammonium oxidizing bacteria (AOB) but inhibit or limit nitrite oxidizing bacteria (NOB). The studies of the AOB and NOB activities have been conducted by state-of-the-art molecular techniques, such as Polymerase Chain Reaction (PCR), Quantitative PCR, denaturing gradient gel electrophoresis (DGGE), Fluorescence in situ hybridization (FISH) technique, Terminal Restriction Fragment Length Polymorphism (T-RFLP), Live/Dead BacLight, and quinone profile. Furthermore, control strategies for obtaining partial nitrification are mainly focused on the pH, temperature, dissolved oxygen concentration, real-time aeration control, sludge retention time, substrate concentration, alternating anoxic and aerobic operation, inhibitor and ultrasonic treatment. Existing problems and further perspectives for the scale-up of partial nitrification are also proposed and suggested.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Nitrous oxide (N2O) emission from wastewater treatment plants (WWTPs) has received increasing attention. This paper presented how N2O emission was significantly reduced in a pilot-scale Carrousel oxidation ditch under reasonable nitrification and denitrification. N2O emission from the reactor was found as low as 0.027% of influent nitrogen, which was much less than that from other processes. Further measurements on spatial variation of N2O emission in the alternative aerobic/anoxic zones with help of a series of batch experiments demonstrated that about 90% of the emission was contributed by nitrifier denitrification (ND). Moreover, the taxonomic analysis based on high through-put 16S rRNA gene sequencing revealed that the high abundance of denitrifying bacteria and nitrite-oxidizing bacteria (NOB) was responsible for low nitrite accumulations and consequent low N2O emissions. However, N2O generation would be greatly increased upon the normal operation being shocked by either ammonia overload or aeration failure of the oxidation ditch system.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Conventional biological wastewater treatment processes are energy-intensive endeavors that yield little or no recovered resources and often require significant external chemical inputs. However, with embedded energy in both organic carbon and nutrients (N, P), wastewater has the potential for substantial energy recovery from a low-value (or no-value) feedstock. A paradigm shift is thus now underway that is transforming our understanding of necessary energy inputs, and potential energy or resource outputs, from wastewater treatment, and energy neutral or even energy positive treatment is increasingly emphasized in practice. As two energy sources in domestic wastewater, we argue that the most suitable way to maximize energy recovery from wastewater treatment is to separate carbon and nutrient (particularly N) removal processes. Innovative anaerobic treatment technologies and bioelectrochemical processes are now being developed as high efficiency methods for energy recovery from waste COD. Recently, energy savings or even generation from N removal has become a hotspot of research and development activity, and nitritation-anammox, the newly developed CANDO process, and microalgae cultivation are considered promising techniques. In this paper, we critically review these five emerging low energy or energy positive bioprocesses for sustainable wastewater treatment, with a particular focus on energy optimization in management of nitrogenous oxygen demand. Taken together, these technologies are now charting a path towards to a new paradigm of resource and energy recovery from wastewater.
Simultaneous biological nutrient removal (SBNR) is the occurrence of biological nutrient removal (BNR) in systems that do not possess defined anaerobic and/or anoxic zones. A review of the relevant literature demonstrates that two mechanisms are primarily responsible for SBNR: (1) the bioreactor macro-environment and (2) the floc microenvironment. Complex hydraulic flow patterns exist in full-scale bioreactors that can result in the cycling of mixed liquor through the different environments needed for BNR. Diffusion resistance further allows oxygen-sufficient and oxygen-deficient zones to develop in activated sludge flocs if the external dissolved oxygen concentration is properly controlled. The diffusion of substrates between these zones allows BNR to occur. Long-term acclimation to the unique environmental conditions occurring in these systems results in the selection of microorganisms well adapted to the low dissolved oxygen concentrations occurring in them. The experience base for the design and operation of SBNR systems is expanding, thereby allowing their more widespread application, especially coupled with conventional mathematical modeling approaches. Computational fluid dynamics is an evolving tool to assist with the design and optimization of SBNR.
Partial nitritation/anammox (PN/A) has been one of the most innovative developments in biological wastewater treatment in recent years. With its discovery in the 1990s a completely new way of ammonium removal from wastewater became available. Over the past decade many technologies have been developed and studied for their applicability to the PN/A concept and several have made it into full-scale. With the perspective of reaching 100 full-scale installations in operation worldwide by 2014 this work presents a summary of PN/A technologies that have been successfully developed, implemented and optimized for high-strength ammonium wastewaters with low C:N ratios and elevated temperatures. The data revealed that more than 50% of all PN/A installations are sequencing batch reactors, 88% of all plants being operated as single-stage systems, and 75% for sidestream treatment of municipal wastewater. Additionally an in-depth survey of 14 full-scale installations was conducted to evaluate practical experiences and report on operational control and troubleshooting. Incoming solids, aeration control and nitrate built up were revealed as the main operational difficulties. The information provided gives a unique/new perspective throughout all the major technologies and discusses the remaining obstacles.
A new process for the removal of nitrogen from wastewater is introduced. The process involves three steps: (1) partial nitrification of NH4+ to NO2−; (2) partial anoxic reduction of NO2− to N2O; and (3) N2O conversion to N2 with energy recovery by either catalytic decomposition to N2 and O2 or use of N2O to oxidize biogas CH4. Steps 1 and 3 have been previously established at full-scale. Accordingly, bench-scale experiments focused on step 2. Two strategies were evaluated and found to be effective: in the first, Fe(II) was used to abiotically reduce NO2− to N2O; in the second, COD stored as polyhydroxybutyrate (PHB) was used as the electron donor for partial heterotrophic reduction of NO2− to N2O. For abiotic reduction with Fe(II), the efficiency of conversion of NO2− to N2O was over 90% with 98% nitrogen removal from water. For partial heterotrophic denitrification, different selection conditions were imposed on acetate- and nitrite-fed communities initially derived from waste activated sludge. No N2O was detected when acetate and nitrite were supplied continuously, but N2O was produced when acetate and nitrite were added as pulses. N2O conversion efficiency was dependent upon the method of addition of acetate and nitrite. When acetate and nitrite were added together (coupled feeding), the N2O conversion efficiency was 9–12%, but when acetate and nitrite additions were decoupled, the N2O conversion efficiency was 60–65%. Decoupled substrate addition selected for a microbial community that accumulated polyhydroxybutyrate (PHB) during an anaerobic period after acetate addition then consumed PHB and reduced NO2− during the subsequent anoxic period. The biological N removal efficiency from the water was 98% over more than 200 cycles. This indicates that decoupled operation can sustain significant long-term N2O production. Compared to conventional nitrogen removal, the three-step process, referred to here as Coupled Aerobic–anoxic Nitrous Decomposition Operation (CANDO), is expected to decrease oxygen requirements, decrease biomass production, increase organic matter available for recovery as biogas methane, and enable energy recovery from nitrogen, but pilot-scale studies are needed.
Almost all present biological processes for treating municipal wastewater have been developed based on the philosophy of biological oxidation with high energy consumption and generation of waste sludge. Given such a situation, the fundamental question of what are the possible ways towards energy self-sufficient biological reclamation of municipal wastewater needs to be addressed urgently. Therefore, this review aims to offer a critical view and a holistic analysis of biological treatment processes with the focus on energy self-sufficiency which indeed is a game changer in the future technology development. The way towards energy self-sufficient operation of biological processes is to maximize energy recovery, while to minimize energy consumption. The examples of such process configurations known as A-B processes are thus discussed. Consequently, this review may offer in-depth insights into the possible directions towards the next-generation biological processes for municipal wastewater reclamation which should be designed as a water-energy-resource factory.
There is very little known about the effectiveness of wastewater treatment systems for saline wastewater generated by seafood processing industries, aquaculture and tourism activities. In particular, the effect of salinity on nitrogen and phosphorus removal in wastewater treatment processes is not well understood. Therefore we devised experiments to examine the treatment of highly saline wastewater, by using artificial seafood processing wastewater, for removal of nitrogen and phosphorus. Lab scale sequencing batch reactors (SBR) were initially operated at low, and then at increasing salt levels, to determine the overall effects of salinity on the nutrient removal performance. The microbial populations during these experiments were monitored to determine the specific effect of salinity on the various bacterial groups responsible for nutrient removal. The methods used were whole cell probing with fluorescently labelled RNA-directed oligonucleotide probes. Experimental data showed that the SBRs achieved good biological nutrient removal (BNR) when salinity levels in the influent were low (0.03% to 0.2% NaCl) but showed difficulties with biological phosphorus removal at salinity levels of 0.5%. It was found that there was a dominance of Gram-positive bacteria with a high mol% G+C in their DNA in the SBR treating wastewater with NaCl at 0.03% to 0.2%. The addition of acetate to improve BNR performance increased the proportion of bacteria from the beta Proteobacterial subclass.
A new biological process for ammonia removal from flows containing hundreds to thousands milligrams NH+4 per litre has been developed at the Delft University of Technology. The SHARON process operates at a high temperature (30–40 °C) and pH (7–8). The process is performed without sludge retention. This enables the prevention of nitrite oxidation, leading to lower operational costs. Denitrification is used to control the pH. A full scale plant was designed (1500 m3) based on kinetic and stoichiometric parameters determined at 1.5 1. scale and model predictions. Total costs are estimated at about $1.7 per kg removed NH4+-N. The first full scale SHARON plant will be operational at the Dokhaven waste water treatment plant in Rotterdam in the beginning of 1998. This contribution focuses on the principles of the process and evaluates conditions for which application seems feasible.
One and a half degrees on biodiversity
Insects are the most diverse group of animals on Earth and are ubiquitous in terrestrial food webs. We have little information about their fate in a changing climate; data are scant for insects compared with other groups of organisms. Warren et al. performed a global-scale analysis of the effects of climate change on insect distribution (see the Perspective by Midgley). For vertebrates and plants, the number of species losing more than half their geographic range by 2100 is halved when warming is limited to 1.5°C, compared with projected losses at 2°C. But for insects, the number is reduced by two-thirds.
Science , this issue p. 791 ; see also p. 714
This study investigated the greenhouse gas emission characteristics and microbial community dynamics with the variation of temperature during partial nitrification. Low temperature weakened nitrite accumulation, and partial nitrification would shift to complete nitrification easily at 15 °C. Based on CO2 equivalents (CO2-eq), partial nitrification process released 2.7 g of greenhouse gases per gMLSS per cycle, and N2O accounted for more than 98% of the total CO2-eq emission. The total CO2-eq emission amount at 35 °C was 45.6% and 153.4% higher than that at 25 °C and 15 °C, respectively. During partial nitrification, the microbial community diversity greatly declined compared with seed sludge. However, the diversity was enhanced at low temperature. The abundance of Betaproteobacteria at class level increased greatly during partial nitrification. Proteobacteria abundance declined while Nitrospira raised at low temperature. The nosZ community abundance was not affected by temperature, although N2O emission was varied with the operating temperature.
This review aims at holistically analyzing the environmental problems associated with nitrous oxide (N2O) emissions by evaluating the most important sources of N2O and its environmental impacts. Emissions from wastewater treatment processes and the industrial production of nitric and adipic acid represent nowadays the most important anthropogenic point sources of N2O. Therefore, state-of-the-art strategies to mitigate the generation and release to the atmosphere of this greenhouse and O3-depleting gas in the waste treatment and industrial sectors are also reviewed. An updated review of the end-of-the-pipe technologies for N2O abatement, both in the waste treatment and industrial sectors, is herein presented and critically discussed for the first time. Despite the consistent efforts recently conducted in the development of cost-efficient and eco-friendly N2O abatement technologies, physical/chemical technologies still constitute the most popular treatments for the control of industrial N2O emissions at commercial scale. The recent advances achieved on biological N2O abatement based on heterotrophic denitrification have opened new opportunities for the development of eco-friendly alternatives for the treatment of N2O emissions. Finally, the main limitations and challenges faced by these novel N2O abatement biotechnologies are identified in order to pave the way for market implementation.
Energy recovery from nitrogen via nitrous oxide by applying e.g., the Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO), is a potential key to more sustainable and energy-efficient wastewater treatment facilities. In this study, laboratory-scale investigations were conducted for the second stage of a continuously operated CANDO process over 84 cycles to test and validate the oxidation reduction potential (ORP) as operational control variable. The ORP was investigated to optimize effluent nitrite (NO2⁻) concentrations, nitrous oxide (N2O) yields and overall process conditions under real feed-stream conditions. Characteristic deviations for stable operational conditions, underload and overload could be derived based on representative cycles. The results revealed that continuously increasing ORP deviations are correlated to the abundance of nitrite in anoxic reaction periods and that the depletion of nitrite and nitrous oxide correlates with switching from a positive to negative ORP gradient. These observations were supported by investigating the dynamics of relevant process parameters of a single cycle. Ultimately, the reactor was successfully operated under dynamic conditions i.e., different chemical oxygen demand to nitrite ratios (COD/N) ratios, and automatically controlled by applying an ORP gradient of −1 mV/min over 20 min as termination criterion for anoxic reaction periods. This operation resulted in stable and reliable NO2⁻ elimination. Additionally, previous observations concerning the necessity of a COD/N ratio of 4 could be confirmed concerning optimal N2O yields. A COD/N ratio of 5 compromised the N2O yield to a higher nitrogen removal rate.
The conventional biological processes for municipal wastewater are facing the challenges of high energy consumption and production of excessive sludge. To address these two emerging issues, this study demonstrated the feasibility to integrate mainstream anammox into an A-2B process for municipal wastewater treatment towards energy-efficient operation with reduced sludge production. In the proposed A-2B process, an anaerobic fixed bed reactor (AFBR) served as A-stage for COD capture, an anammox moving bed biofilm reactor (MBBR) was employed as B2-stage, which received effluent containing nitrite from a sequencing batch reactor (SBR) at B1-stage. The results showed that under the operation conditions studied, 58% of influent COD was converted methane gas at A-stage, and 87% total inorganic nitrogen (TIN) removal was achieved with the effluent TIN concentration of 6.5 mg /L. Moreover, it was shown that at least 75% of sludge reduction was obtained due to the COD capture at A-stage. The high-throughput sequencing analysis further revealed that Candidatus Kuenenia was the dominant genus responsible for the observed anammox at B2-stage MBBR. This study clearly demonstrated a novel process configuration for sustaining mainstream anammox for municipal wastewater reclamation towards energy-efficient operation with minimized sludge production.
A Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) was performed over five months to investigate the performance and dynamics of nitrogen elimination and nitrous oxide production from digester reject water under real feed-stream conditions. A 93% conversion of ammonium to nitrite could be maintained for adapted seed sludge in the first stage (nitritation). The second stage (nitrous denitritation), inoculated with conventional activated sludge, achieved a conversion of 70% of nitrite to nitrous oxide after only 12 cycles of operation. The development of an alternative feeding strategy and the addition of a coagulant (FeCl3) facilitated stable operation and process intensification. Under steady-state conditions, nitrite was reliably eliminated and different nitrous oxide harvesting strategies were assessed. Applying continuous removal increased N2O yields by 16% compared to the application of a dedicated stripping phase. These results demonstrate the feasible application of the CANDO process for nitrogen removal and energy recovery from ammonia rich wastewater.
In order to evaluate the effects of carbon-nitrogen ratio (CNR) on nitrous oxide (N2O) emission and quantify N2O spatial distribution in subsurface wastewater infiltration system (SWIS), layered sampling method was introduced. Results showed that low N2O emission rate (1.43 mg/m²·h) and conversion rate (0.1% accounting for influent TN) were obtained when CNR increased up to as high as 10. The highest N2O emission (3.14 mg/m²·h) was observed at CNR of 6. Instead, independent of CNR variations, 0–75 cm was the main contributor for N2O emission. The results indicated that layered sampling method is necessary in revealing N2O spatial distribution in soil layers. Carbon source availability and nitrogen load and their ratio (i.e. CNR) determined N2O emission rate. CNR of medium level leads to an increase in N2O emission rate.
Nitrous oxide (N2O) is a potent green-house gas, but has also recently been acknowledged as sustainable energy source that can intentionally be produced by bioreactor systems such as the Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO). In this study, the application potential of a porous hollow fiber membrane contactor has been assessed at expected conditions of an operating CANDO system in shell-side liquid feed operation for N2O removal. At varying feed concentrations, liquid and gas flow rates, off-gas concentrations, removal efficiencies, trans-membrane fluxes and mass-flows have been assessed and compared to previous studies on CO2. Under the applied operational conditions, the gas flow rate had no significant effect on the results. Removal efficiencies up to 77% of the module feed load demonstrated a high application potential for the CANDO process and indicate a promising removal potential greater 90% in reference to typical initial substrate loads in an operating CANDO system. Additionally, considerably higher off-gas concentrations compared to recently published results applying conventional stripping technology of 3700 ppmv were generated reducing sweeping gas demand by 70%. The mass transfer was dominated by the superficial velocity on the liquid side and its behavior could be well described by Sherwood correlations. However, previously published mass transfer correlations over-estimated the results. Hence, a more appropriate correlation is presented to describe the observations of this study.
The books provides a timely analysis in support of a paradigm shift in the field of wastewater management, from ‘treatment for disposal’ to ‘treatment for reuse’ by offering a variety of value propositions for water, nutrient and energy recovery which can support cost savings, cost recovery, and profits, in a sector that traditionally relies on public funding. The book provides new insights into the economics of wastewater use, applicable to developed and developing countries striving to transform wastewater from an unpleasant liability to a valuable asset and recasting urbanization from a daunting challenge into a resource recovery opportunity.
In order to make a better understanding of the characteristics of N2O emission in A/O wastewater treatment plant, full-scale and pilot-scale experiments were carried out and a back propagation artificial neural network model based on the experimental data was constructed to make a precise prediction of N2O emission. Results showed that, N2O flux from different units followed a descending order: aerated grit tank>oxic zone≫anoxic zone>final clarifier>primary clarifier, but 99.4% of the total emission of N2O (1.60% of N-load) was monitored from the oxic zone due to its big surface area. A proper DO control could reduce N2O emission down to 0.21% of N-load in A/O process, and a two-hidden-layers back propagation model with an optimized structure of 4:3:9:1 could achieve a good simulation of N2O emission, which provided a new method for the prediction of N2O emission during wastewater treatment.
Nitrous oxide (N2O) is an unwanted byproduct during biological nitrogen removal processes in wastewater. To establish strategies for N2O mitigation, a better understanding of production mechanisms and their controls is required. A novel stable isotope labeling approach using 15N and 18O was applied to investigate pathways and controls of N2O production by biomass taken from a full-scale nitritation-anammox reactor. The experiments showed that heterotrophic denitrification was a negligible source of N2O under oxic conditions (≥ 0.2 mg O2 L-1). Both hydroxylamine oxidation and nitrifier denitrification contributed substantially to N2O accumulation across a wide range of conditions with varying concentrations of O2, NH4+ and NO2-. The O2 concentration exerted the strongest control on net N2O production with both production pathways stimulated by low O2, independent of NO2- concentrations. The stimulation of N2O production from hydroxylamine oxidation at low O2 was unexpected and suggests that more than one enzymatic pathway may be involved in this process. N2O production by hydroxylamine oxidation was further stimulated by NH4+, while nitrifier denitrification at low O2 levels was stimulated by NO2- at levels as low as 0.2 mM. Our study shows that 15N and 18O isotope labeling is a useful approach for direct quantification of N2O production pathways applicable to diverse environments.
This paper describes the mechanism of nitrogen and phosphorus removal by activated sludge process, and introduces several conventional nitrogen and phosphorus bioremoval processes, namely sequencing batch reactor (SBR), anaerobic-anoxic-aerobic (AAO), oxidation ditch, and bio-doubling process (BDP). Many improved technologies were invented to compensate for the defects of conventional activated sludge process Nitrogen and phosphorus bioremoval by activated sludge process have many similarities and conflicts, including different sludge characteristics and competition for carbon sources that affect the results of the simultaneous nitrogen and phosphorus removal. Therefore, a series of countermeasures to resolve such conflicts are reviewed. Economy, sefficiency and low energy consumption will be the developing trends of wastewater treatment in the future.
Nitrous oxide (N2O) is an important pollutant which is emitted during the biological nutrient removal (BNR) processes of wastewater treatment. Since it has a greenhouse effect which is 265 times higher than carbon dioxide, even relatively small amounts can result in a significant carbon footprint. Biological nitrogen (N) removal conventionally occurs with nitrification/denitrification, yet also through advanced processes such as nitritation/denitritation and completely autotrophic N-removal. The microbial pathways leading to the N2O emission include hydroxylamine oxidation and nitrifier denitrification, both activated by ammonia oxidizing bacteria, and heterotrophic denitrification. In this work, a critical review of the existing literature on N2O emissions during BNR is presented focusing on the most contributing parameters. Various factors increasing the N2O emissions either per se or combined are identified: low dissolved oxygen, high nitrite accumulation, low chemical oxygen demand to nitrogen ratio, slow growth of denitrifying bacteria, uncontrolled pH and temperature. However, there is no common pattern in reporting the N2O generation amongst the cited studies, a fact that complicates its evaluation. When simulating N2O emissions, all microbial pathways along with the potential contribution of abiotic N2O production during wastewater treatment at different dissolved oxygen/nitrite levels should be considered. The undeniable validation of the robustness of such models calls for reliable quantification techniques which simultaneously describe dissolved and gaseous N2O dynamics. Thus, the choice of the N-removal process, the optimal selection of operational parameters and the establishment of validated dynamic models combining multiple N2O pathways are essential for studying the emissions mitigation.
Deammonification’s performance and associated nitrous oxide emissions (N2O) depend on operational conditions. While studies have investigated factors for high performances and low emissions separately, this study investigated optimizing deammonification performance while simultaneously reducing N2O emissions. Using a design of experiment (DoE) method, two models were developed for the prediction of the nitrogen removal rate and N2O emissions during single-stage deammonification considering three operational factors (i.e., pH value, feeding and aeration strategy). The emission factor varied between 0.7 ± 0.5% and 4.1 ± 1.2% at different DoE-conditions. The nitrogen removal rate was predicted to be maximized at settings of pH 7.46, intermittent feeding and aeration. Conversely, emissions were predicted to be minimized at the design edges at pH 7.80, single feeding, and continuous aeration. Results suggested a weak positive correlation between the nitrogen removal rate and N2O emissions, thus, a single optimizing operational set-point for maximized performance and minimized emissions did not exist.
During 2015-2016, record temperatures triggered a pan-tropical episode of coral bleaching, the third global-scale event since mass bleaching was first documented in the 1980s. Here we examine how and why the severity of recurrent major bleaching events has varied at multiple scales, using aerial and underwater surveys of Australian reefs combined with satellite-derived sea surface temperatures. The distinctive geographic footprints of recurrent bleaching on the Great Barrier Reef in 1998, 2002 and 2016 were determined by the spatial pattern of sea temperatures in each year. Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, suggesting that local protection of reefs affords little or no resistance to extreme heat. Similarly, past exposure to bleaching in 1998 and 2002 did not lessen the severity of bleaching in 2016. Consequently, immediate global action to curb future warming is essential to secure a future for coral reefs.
Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) is a promising emerging bioprocess for wastewater treatment that enables direct energy recovery from nitrogen (N) in three steps: (1) ammonium oxidation to nitrite; (2) denitrification of nitrite to nitrous oxide (N2O); and (3) N2O conversion to N2 with energy generation. However, CANDO does not currently target phosphorus (P) removal. Here, we demonstrate that denitrifying polyphosphate accumulating organism (PAO) enrichment cultures are capable of catalyzing simultaneous biological N and P removal coupled to N2O generation in a 2nd generation CANDO process, CANDO+P. Over seven months (>300 cycles) of operation of a prototype lab-scale CANDO+P sequencing batch reactor treating synthetic municipal wastewater, we observed stable and near complete N removal accompanied by sustained high rate, high yield N2O production with partial P removal. A substantial increase in abundance of the PAO “Candidatus Accumulibacter phosphatis” was observed, from 5% of the total bacterial community in the inoculum to over 50% after four months. PAO enrichment was accompanied by a strong shift in the dominant Accumulibacter population from Clade IIC to Clade IA, based on qPCR monitoring of polyphosphate kinase 1 (ppk1) gene variants. Our work demonstrates the feasibility of combining high rate, high yield N2O production for bioenergy production with combined N and P removal from wastewater, and it further suggests a putative denitrifying PAO niche for Accumulibacter Clade IA.
The use of seawater and production of some chemicals produce a lot of saline wastewater. There are many treatment technologies for treating saline wastewater, such as physical, chemical and biological treatment. Biological treatment processes, especially the activated sludge processes, show advantages over other processes due to its cost-effectiveness and avoiding of secondary pollution, and many researches have been performed in this field. In this paper, the progresses of researches about the effect of salinity on activated sludge and its microorganisms were reviewed which included the effect of salinity on sludge structure and properties, microbial species and biomass, microbial physiological changes, and microbial molecules and cells. The mechanisms of the effect of salinity on sludge and the microbes were also summarized. Additionally, the feasibility of treatment of saline wastewater by using the acclimated salt tolerant activated sludge was evaluated. Future research needs were also proposed which include the study on the mechanisms of salt stress on activated sludge microorganisms at cellular and molecular levels and enzyme activity, screening and acclimation of salt-tolerant bacteria including halophiles, and optimizing of process parameters for saline wastewater treatment.
The joint effect of wastewater salinity and hydrocarbons on nitrous oxide emission was investigated. The membrane bioreactor pilot plant was operated with two phases: i. biomass acclimation by increasing salinity from 10 gNaCl L-1 to 20 gNaCl L-1 (Phase I); ii. hydrocarbons dosing at 20 mg L-1 with a constant salt concentration of 20 gNaCl L-1 (Phase II). The Phase I revealed a relationship between nitrous oxide emissions and salinity. During the end of the Phase I, the activity of nitrifiers started to recover, indicating a partial acclimatization. During the Phase II, the hydrocarbon shock induced a temporary inhibition of the biomass with the suppression of nitrous oxide emissions. The results revealed that the oxic tank was the major source of nitrous oxide emission, likely due to the gas stripping by aeration. The joint effect of salinity and hydrocarbons was found to be crucial for the production of nitrous oxide.
The nitrous oxide (N2O) and methane (CH4) emissions were measured from a municipal wastewater treatment plant (WWTP) using a flux chamber to determine the emission factors. The WWTP treats sewage using both the activated-sludge treatment and anaerobic/anoxic/aerobic (A2O) methods. Measurements were performed in the first settling, aeration, and secondary settling basins, as well as in the sludge thickener, sludge digestion tank, and A2O basins. The total emission factors of N2O and CH4 from the activated-sludge treatment were 1.256 g N2O/ kg total nitrogen (TN) and 3.734 g CH4/ kg biochemical oxygen demand (BOD5), respectively. Those of the advanced treatment (A2O) were 1.605 g N2O/ kg TN and 4.022 g CH4/ kg BOD5, respectively. These values are applicable as basic data to estimate greenhouse gas emissions.
Denitrification is the dissimilatory reduction of nitrate to nitrogen gas. This respiratory process requires four enzymes that produce three obligatory intermediates prior to production of the terminal product. Denitrification is found in diverse array of microbes including members of both bacteria and archaea. However, no bacterium has been described that solely depends on denitrification as a form of energy generation. All denitrifiers, with one exception, are aerobes. Genome sequencing has provided a better appreciation of the distribution of denitrification genes among microbes. Complete denitrification, the reduction of nitrate to N2, is less frequent than partial denitrification among sequenced bacteria. Partial denitrification chains of nearly all possible arrangments have been found. This includes chains with only a single enzyme or discontinuous chains of two or more enzymes. Nitrate reductase catalyzes the reduction of nitrate to nitrite and is used in a number of pathways other than denitrification; therefore, its distribution has not been a focus of this chapter. Nitrite reductase catalyzes the reduction of nitrite to nitric oxide and is the defining reaction of denitrification since it is the first step to produce a gaseous nitrogen oxide. There are two unrelated types of nitrite reductase, one of which has copper cofactors while the other contains heme-bound iron. The copper form has several different subtypes with N- and C-terminal extensions containing metal-binding sites. Some members of the Actinobacteria have a particularly large copper nitrite reductase with a membrane-bound domain of unknown function. Nitric oxide reductase catalyzes the reduction of nitric oxide to nitrous oxide. This enzyme is membrane bound and occurs in two subtypes referred to as cNor and qNor. The former receives electrons from cytochrome c while the latter carries an N-terminal extension allowing it to oxidize quinol. Nitrous oxide reductase is a soluble copper-containing enzyme with one of the copper centers, designated the CuZ center, being unique to this enzyme. While most model denitrifiers use denitrification to support growth when oxygen is limiting, this may not be the case in all bacteria that contain genes encoding denitrification-associated nitrogen oxide reductases. Bacteria with partial chains consisting of a single enzyme may use that enzyme for alternative functions. For example, some Staphylococcus aureus subspecies aureus strains only contain nitric oxide reductase which is likely used for detoxification of nitric oxide. There are a number of bacteria which only contain nitrite reductase and the function of this enzyme is unclear in these organisms since its turnover will produce nitric oxide, which is toxic due to its reactivity with metal centers and other compounds. Environmental studies have found denitrification genes are nearly universal in environments that receive some exposure to oxygen. Quantitative studies have found that the genes for nitrous oxide reductase are frequently underrepresented compared to other denitrification genes. While common in soil and aquatic environments, denitrifiers are also found in association with humans. Sequencing of both skin and oral microbiomes has revealed a significant number of denitrifiers, consistent with the occurrence of both nitrate and nitrite in these areas. © 2013 Springer-Verlag Berlin Heidelberg. All rights are reserved.
The Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) is a new process for wastewater treatment that removes nitrogen from wastewater and recovers energy from the nitrogen in three steps: (1) NH4+ oxidation to NO2-, (2) NO2- reduction to N2O, and (3) N2O conversion to N2 with energy production. Here we demonstrate that Type II methanotrophic enrichments can mediate step two by coupling oxidation of poly(3-hydroxybutyrate) (P3HB) to NO2- reduction. Enrichments grown with NH4+ and NO2- were subject to alternating 48 h aerobic and anoxic periods, in which CH4 and NO2- were added together in a "coupled" mode of operation or separately in a "decoupled mode". Community structure was stable in both modes and dominated by Methylocystis. In the coupled mode, production of P3HB and N2O was low. In the decoupled mode, significant P3HB was produced, and oxidation of P3HB drove reduction of NO2- to N2O with ~70% conversion for > 30 cycles (120 d). In batch tests of wasted cells from the decoupled mode, N2O production rates increased at low O2 or high NO2- levels. The results are significant for the development of engineered processes that remove nitrogen from wastewater and for understanding of conditions that favor environmental production of N2O.
The effects of temperature on nitrous oxide (N2O) accumulation during denitrification and denitritation were investigated. Batch experiments were performed to measure N2O accumulation at 25 and 35 °C. More N2O accumulation was observed during denitritation at the higher temperature as compared with full denitrification and low temperature tests. The highest nitrite concentration tested in this study (25 mg/L NO2 (-)N and pH 8.0) did not show inhibitory effect on N2O reduction. It was found that the major cause of more N2O accumulation during denitrification at higher temperature was due to higher N2O production rate and lower N2O solubility. Specific nitrate, nitrite, and N2O reduction rates increased 62, 61, and 41 %, respectively, when temperature rose from 25 to 35 °C. The decrease of N2O solubility in mixed liquor at 35 °C (when compared to 25 °C) resulted in faster diffusing rate of N2O from liquid to gas phase. It was also more difficult for gas phase N2O to be re-dissolved. The diffused N2O was then accumulated in the headspace, which was not available for denitrification by denitrifiers. The results of this study suggest higher temperature may worsen N2O emission from wastewater treatment plants (WWTPs).
In recent years, the operating cost of sewage treatment plants (STPs) in some parts of the world has been rising due to increases in the cost of energy. STPs have focused on energy reduction and recovery from treatment processes in order to lower energy consumption. The development involves the improvement of capital set-up for treatment plants in terms of equipment upgrading/plant sizing as well as exploration of novel technologies for sewage, excess sludge treatment and biogas recovery. This review compares the current technologies applied in STPs around the world and discusses these technologies and facilities which may enhance energy reduction and recovery in sewage treatment.
Experiments on flammability limits, ignition energies, and flame speeds were carried out in a 11.25- and a 400-liter combustion vessel at initial pressures and temperatures of 100 kPa and 295 K, respectively. Flammability maps of hydrogen–nitrous oxide–nitrogen, methane–nitrous oxide–nitrogen, ammonia–nitrous oxide–nitrogen, and ammonia–nitrous oxide–air, as well as lean flammability limits of various hydrogen–methane–ammonia–nitrous oxide–oxygen–nitrogen mixtures were determined. Ignition energy bounds of methane–nitrous oxide, ammonia–nitrous oxide, and ammonia–nitrous oxide–nitrogen mixtures have been determined and the influence of small amounts of oxygen on the flammability of methane–nitrous oxide–nitrogen mixtures has been investigated. Flame speeds have been measured and laminar burning velocities have been determined for ammonia–air–nitrous oxide and various hydrogen–methane–ammonia–nitrous oxide–oxygen–nitrogen mixtures. Lower and upper flammability limits (mixing fan on, turbulent conditions) for ignition energies of 8 J are: H2–N2O: 4.5 ∼ 5.0% H2(LFL), 76 ∼ 80% H2(UFL); CH4–N2O: 2.5 ∼ 3.0% CH4(LFL), 43 ∼ 50% CH4(UFL); NH3–N2O: 5.0 ∼ 5.2% NH3(LFL), 67.5 ∼ 68% NH3(UFL). Inerting concentrations are: H2–N2O–N2: 76% N2; CH4–N2O–N2: 70.5% N2; NH3–N2O–N2: 61% N2; NH3–N2O–air: 85% air. Flammability limits of methane–nitrous oxide–nitrogen mixtures show no pronounced dependence on small amounts of oxygen (<5%). Generally speaking, flammable gases with large initial amounts of nitrous oxide or ammonia show a strong dependence of flammability limits on ignition energy.
The Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) is a new process for wastewater treatment that removes nitrogen from wastewater and recovers energy from the nitrogen in three steps: (1) NH4+ oxidation to NO2-; (2) NO2- reduction to N2O gas; and, (3) N2O conversion to N2 with energy production. In this work, we optimize Steps 1 and 2 for anaerobic digester centrate, and we evaluate Step 3 for a full-scale biogas-fed internal combustion engine. Using a continuous stirred reactor coupled to a bench-scale sequencing batch reactor, we observed sustained partial oxidation of NH4+ to NO2- and sustained (3 months) partial reduction of NO2- to N2O (75-80% conversion, mass basis), with >95% nitrogen removal (Step 2). Alternating pulses of acetate and NO2- selected for Comamonas (38%), Ciceribacter (16%), and Clostridium (11%). Some species stored polyhydroxybutyrate (PHB) and coupled oxidation of PHB to reduction of NO2- to N2O. Some species also stored phosphorus as polyphosphate granules. Injections of N2O into a biogas-fed engine at flow rates simulating a full-scale system increased power output by 5.7-7.3%. The results underscore the need for more detailed assessment of bioreactor community ecology and justify pilot- and full- scale testing.
Given the interest in using hydrocarbon-nitrous oxide propellant combinations in space propulsion applications, mixtures of various hydrocarbons (CH4, C2H2 and C3H8) and ni- trous oxide were studied to experimentally and numerically determine the laminar flame speeds at near atmospheric pressure (0:8 atm). The literature is quite limited with these data, and the few experiments conducted show a large disparity in many cases. In this work, a comprehensive hydrocarbon mechanism in the literature was integrated with a nitrogen chemistry sub-model, and computational flame speed results using this mechanism are compared with experimental results. These results include flame speed measurements for CH 4-, C2H2- and C3H 8-nitrous oxide flames, diluted with nitrogen (N2O/(N 2O + N2)= 0:42). For all three fuels, the model under-predicted the measured laminar flame speeds with the differences being more significant under fuel-rich conditions. Future work will focus on measuring flame speeds over a range of system pressure, other dilution levels, as well as optimizing the kinetic mechanism for these flame Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc.
+ per litre has been developed at the Delft University of Technology. The SHARON process operates at a high temperature (30–40 °C) and pH (7–8). The process is performed without sludge retention. This enables the prevention of nitrite oxidation, leading to lower operational costs. Denitrification is used to control the pH. A full scale plant was designed (1500 m3) based on kinetic and stoichiometric parameters determined al 1.5.1. scale and model predictions. Total costs are estimated at about $1.7 per kg removed NH4+-N. The first full scale SHARON plant will be operational at the Dokhaven waste water treatment plant in Rotterdam in the beginning of 1998. This contribution focuses on the principles of the process and evaluates conditions for which application seems feasible.