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

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

Reliable modelling of sulfide and methane production in sewer systems is required for efficient sewer emission management. Wastewater compositions affect sulfide and methane production kinetics through both its short-term variation influencing the substrate availability to sewer biofilms, and its long-term variation affecting the sewer biofilm structure. While the short-term effect is well considered in existing sewer models with the use of Monod or half-order equations, the long-term effect has not been explicitly considered in current sewer models suitable for network modelling. In this study, the long-term effect of wastewater compositions on sulfide and methane production activities in rising main sewers was investigated. A detailed biofilm model was firstly developed, and then calibrated and validated using experimental data measured during the entire biofilm development period of a laboratory sewer reactor. Based on scenario simulations using the detailed biofilm model, empirical equations describing the long-term effect of sulfate and sCOD (soluble chemical oxygen demand) concentrations on k H2S (the maximum sulfide production rate of sewer biofilm) and k CH4 (the maximum methane production rate of sewer biofilm) were proposed. These equations require further verification in future studies before their potential integration into network-wide sewer models. [ABSTRACT FROM AUTHOR]

"Sludge-drying lagoons" are a preferred sludge treatment and drying method in tropical and subtropical areas due to the low construction and operational costs. However, this method may be a potential significant source of methane (CH4) because some of the organic matter would be microbially metabolized under anaerobic conditions in the lagoon. The quantification of CH4 emissions from lagoons is difficult due to the expected temporal and spatial variations over a lagoon maturing cycle of several years. Sporadic ebullition of CH4, which cannot be easily quantified by conventional methods such as floating hoods, is also expected. In this study, a novel method based on mass balances was developed to estimate the CH4 emissions and was applied to a full-scale sludge-drying lagoon over a three year operational cycle. The results revealed that processes in a sludge-drying lagoon would emit 6.5 kg CO2-e per megaliter of treated sewage. This would represent a quarter to two-thirds of the overall greenhouse gas (GHG) emissions from wastewater-treatment plants (WWTPs). This work highlights the fact that sludge-drying lagoons are a significant source of CH4 that adds substantially to the overall GHG footprint of WWTPs despite being recognized as a cheap and energy-efficient means of drying sludge. [ABSTRACT FROM AUTHOR]

The presence of a high level of dissolved methane (e.g., 20–26 g m −3 ) in the anaerobic sludge digestion liquor represents a major challenge to the treatment of this stream, as its emission to the atmosphere contributes significantly to the carbon footprint of wastewater treatment. Here we propose a new approach to simultaneous ammonium and dissolved methane removal from the anaerobic digestion liquor through integrating partial nitritation-Anammox and denitrifying anaerobic methane oxidation (DAMO) processes in a single-stage membrane biofilm reactor (MBfR). In such an MBfR, the anaerobic digestion liquor is provided in the bulk liquid, while oxygen is supplied through gas-permeable membranes to avoid dissolved methane stripping. A previously developed model with appropriate extensions was applied to assess the system performance under different operational conditions and the corresponding microbial interactions. Both influent surface loading (or hydraulic retention time) and oxygen surface loading are found to significantly influence the total nitrogen (TN) and dissolved methane removal, which jointly determine the overall system performance. The counter diffusion and concentration gradients of substrates cause microbial stratification in the biofilm, where ammonia-oxidizing bacteria (AOB) attach close to the membrane surface (biofilm base) where oxygen and ammonium are available, while Anammox and DAMO microorganisms jointly grow in the biofilm layer close to the bulk liquid where methane, ammonium, and nitrite are available with the latter produced by AOB. These results provide first insights and useful information for the design and operation of this new technology for simultaneous ammonium and dissolved methane removal in its potential future applications. [ABSTRACT FROM AUTHOR]

Recent studies have shown that sewer systems produce and emit a significant amount of methane. Methanogens produce methane under anaerobic conditions in sewer biofilms and sediments, and the stratification of methanogens and sulfate-reducing bacteria may explain the simultaneous production of methane and sulfide in sewers. No significant methane sinks or methanotrophic activities have been identified in sewers to date. Therefore, most of the methane would be emitted at the interface between sewage and atmosphere in gravity sewers, pumping stations, and inlets of wastewater treatment plants, although oxidation of methane in the aeration basin of a wastewater treatment plant has been reported recently. Online measurements have also revealed highly dynamic temporal and spatial variations in methane production caused by factors such as hydraulic retention time, area-to-volume ratio, temperature, and concentration of organic matter in sewage. Both mechanistic and empirical models have been proposed to predict methane production in sewers. Due to the sensitivity of methanogens to environmental conditions, most of the chemicals effective in controlling sulfide in sewers also suppress or diminish methane production. In this paper, we review the recent studies on methane emission from sewers, including the production mechanisms, quantification, modeling, and mitigation. [ABSTRACT FROM AUTHOR]

Abstract: Methane formation and emission in sewer systems has not received as much attention as hydrogen sulphide formation. Through field measurements from two rising mains, with an average sewage temperature of 28.4 and 26.6°C, respectively, at the time of sampling, this study shows that a significant amount of methane can be produced in sewer systems, and that this production is positively correlated with the hydraulic retention time of wastewater in these systems. The experimental results from a laboratory-scale sewer system fed with real sewage with a temperature of approximately 21°C confirmed these field observations and further revealed that methanogenesis and sulphate reduction occur simultaneously in sewers, with methane production contributing considerably more to the loss of soluble COD in sewers than sulphate reduction. The production of methane in sewers at levels revealed by this study is a serious environmental concern as it potentially results in greenhouse emissions that is comparable to that caused by the energy consumption for the treatment of the same wastewater. Further, methane production in sewers influences sulphide production and its management due to the competition between methanogens and sulphate-reducing bacteria for potentially the same electron donors. The potential interactions between sulphate-reducing and methanogenic bacteria in sewer networks are discussed. [Copyright &y& Elsevier]

Integrating denitrifying anaerobic methane oxidation (DAMO) with Anammox provides alternative solutions to simultaneously remove nitrogen and mitigate methane emission from wastewater treatment. However, the practical application of DAMO has been greatly limited by slow-growing DAMO microorganisms living on low-solubility gaseous methane. In this work, DAMO and Anammox co-cultures were fast enriched using high concentration of mixed sludges from various environments, and achieved nitrogen removal rate of 76.7 mg NH 4 +-N L−1 d−1 and 87.9 mg NO 3 −-N L−1 d−1 on Day 178. Subsequently, nitrogen removal rate significantly decreased but recovered quickly through increasing methane flushing frequency, indicating methane availability could be the limiting factor of DAMO activity. Thus, this work developed a novel M embrane A erated M embrane B ioreactor (MAMBR), which equipped with gas permeable membrane for efficient methane delivery and ultrafiltration membrane for complete biomass retention. After inoculated with enriched sludge, nitrogen removal rates of MAMBR were significantly enhanced to 126.9 mg NH 4 +-N L−1 d−1 and 158.8 mg NO 3 −-N L−1 d−1 by membrane aeration in batch test. Finally, the MAMBR was continuously fed with synthetic wastewater containing ammonium and nitrite to mimic the effluent from partial nitritation. When steady state with nitrogen loading rate of 2500 mg N L−1 d−1 was reached, the MAMBR achieved total nitrogen removal of 2496.7 mg N L−1 d−1, with negligible nitrate in effluent (~6.5 mg NO 3 −-N L−1). 16S rRNA amplicon sequencing and fluorescence in situ hybridization revealed the microbial community dynamics during enrichment and application. The high performance of nitrogen removal (2.5 kg N m−3 d−1) within 200 days operation and excellent biomass retention capacity (8.67 kg VSS m−3) makes the MAMBR promising for practical application of DAMO and Anammox in wastewater treatment. Unlabelled Image • Methane supply by membrane aeration in floc system significantly enhanced nitrogen removal performance. • Nitrogen removal rate of 2.5 kg N m−3 d−1 was achieved within 200 days in MAMBR. • The MAMBR is a practical technology for application of Anammox and DAMO processes. • Microbial community dynamics were revealed during enrichment and application. [ABSTRACT FROM AUTHOR]