Access the full text.
Sign up today, get DeepDyve free for 14 days.
P. Velasco, V. Jegatheesan, Kandasamy Thangavadivel, M. Othman, Yang Zhang (2021)A focused review on membrane contactors for the recovery of dissolved methane from anaerobic membrane bioreactor (AnMBR) effluents.
Wichitpan Rongwong, Kunli Goh, Tae-Hyun Bae (2018)Energy analysis and optimization of hollow fiber membrane contactors for recovery of dissolve methane from anaerobic membrane bioreactor effluent
Journal of Membrane Science, 554
Xiaoyu Zhang, Jun Gu, Yu Liu (2022)Necessity of direct energy and ammonium recovery for carbon neutral municipal wastewater reclamation in an innovative anaerobic MBR-biochar adsorption-reverse osmosis process.
Water research, 211
Brian Crone, J. Garland, G. Sorial, L. Vane (2016)Significance of dissolved methane in effluents of anaerobically treated low strength wastewater and potential for recovery as an energy product: A review.
Water research, 104
Jun Gu, Guangjing Xu, Yu Liu (2017)An integrated AMBBR and IFAS-SBR process for municipal wastewater treatment towards enhanced energy recovery, reduced energy consumption and sludge production.
Water research, 110
(2020)How much carbon dioxide is produced per kilowatt-hour of U.S. electricity generation? Availiable onine at
Ze-hua Liu, Hua Yin, Z. Dang, Yu Liu (2014)Dissolved methane: a hurdle for anaerobic treatment of municipal wastewater.
Environmental science & technology, 48 2
Xuesong Li, Abhishek Dutta, Qirong Dong, Sasha Rollings-Scattergood, Jongho Lee (2019)Dissolved Methane Harvesting Using Omniphobic Membranes for Anaerobically Treated Wastewaters
Environmental Science & Technology Letters
Front. Environ. Sci. Eng. 2022, 16(4): 54 https://doi.org/10.1007/s11783-022-1537-4 PERSPECTIVE Dissolved methane in anaerobic effluent: Emission or recovery? Xiaoyuan Zhang1, Jun Gu2, Shujuan Meng3, Yu Liu ( )1,4 1 Advanced Environmental Biotechnology Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University, Singapore 637141, Singapore 2 Department of Environmental Science and Engineering, School of Energy and Environment, Southeast University, Nanjing 210096, China 3 School of Space and Environment, Beihang University, Beijing 100191, China 4 School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore The Author(s) 2022. This article is published with open access at link.springer.com and journal.hep. com.cn such, increasing effort has been devoted to developing Abstract Various anaerobic processes have been dissolved methane recovery methods, e.g. mechanical explored for the energy-efficient treatment of municipal degassing (Gu et al., 2017), membrane contactors (Li wastewater. However, dissolved methane in anaerobic et al., 2019; Rongwong et al., 2018) etc. It should also be effluent appears to be a barrier towards the energy and aware that the assessments of various recovery methods carbon neutrality of wastewater treatment. Although several are primarily motivated by the energy recovery and dissolved methane recovery methods have been developed, consumption, without a thorough consideration of their their engineering feasibility and economic viability have environmental sustainability and economic viability. In not yet been assessed in a holistic manner. In this this perspective, we intend to offer additional insights perspective, we thus intend to offer additional insights into into the cost-benefit of dissolved methane recovery the cost-benefit of dissolved methane recovery against its against its emission. emission. Given an anaerobic effluent with dissolved methane concentration of 21 g/m3 (solubility of methane at 25 °C) Keywords Anaerobic treatment, Municipal wastewater, (Li et al., 2019; Liu et al., 2014), without proper recovery, Dissolved methane, Methane recovery, Carbon emission the dissolved methane will inevitably be released into the environment. In consideration of a short lifetime of methane, its 20-year global warming potential has been With the fast-evolving global climate change, the energy recommended by the Intergovernmental Panel on Climate and carbon neutral municipal wastewater treatment is Change (IPCC) to be 84−87 folds of carbon dioxide. under the spotlight. Different from the conventional Thus, this amount of dissolved methane will cause activated sludge process and its variants which are a carbon emission of (21 g/m3) × 84=1.76 kg CO e/m3 primarily based on the concept of biological oxidation, wastewater treated, while compromising the overall anaerobic processes have been actively explored for energy recovery efficiency. In fact, such a carbon emission direct COD capture from municipal wastewater, while is equivalent to the carbon emission from generating maximizing the energy recovery and minimizing waste (1.76 kg CO e/m3)/(0.99 kg CO e/kWh)=1.78 kWh/m3 sludge generation (Liu et al., 2019; Zhang et al., 2022). 2 2 of electricity through coal combustion, with a factor However, it should be noted that anaerobic effluent of 0.99 kg CO e/kWh of electricity produced from contains considerable amount of dissolved methane whose 2 coal (U.S.-Energy-Information-Administration, 2020). It release into the environment (Liu et al., 2014) would is obvious that dissolved methane in anaerobic effluent is seriously compromise the energy recovery potential and becoming a barrier towards the energy- and carbon-neutral contribute to significant greenhouse gas emission. As municipal wastewater treatment if a proper measure is not in place for its recovery. Received December 31, 2021; Revised February 10, 2022; Accepted So far, several methods have been developed for February 20, 2022; Available online March 28, 2022 dissolved methane recovery. For example, an average ✉ Corresponding author dissolved methane concentration of 17.1 g/m3 was E-mail: email@example.com observed in an anaerobic effluent at 30 °C, of which 2 Front. Environ. Sci. Eng. 2022, 16(4): 54 nearly 90% could be recovered by means of a mechanical (200,000 m3/d) × (21 g/m3)/(0.8 g/(m2·h))= 218,750 m2, degasser at an energy cost of 0.12 kWh/m3 (Gu et al., indicating a significant increase in the captital investment 2017). Therefore, the recoverable energy could be and maintenance cost. In addition, membrane wetting, calculated to be (15.4 g/m3)/(16 g/mol) × 22.4 L/mol fouling and concentration polarization will make the ×37.8 MJ/m3 (methane energy content) × 35% (electricity operation of membrane contactors more challenging conversion efficiency)/(3.6 MJ/kWh) = 0.079 kWh/m3 (Crone et al., 2016). Moreover, the energy required for wastewater treated. Thus, the net energy utilized for upgrading and compressing recovered dissolved methane degassing was estimated to be 0.041 kWh/ m3 wastewater should also be considered, which had been reported to be treated, which could lead to a carbon emission by about 0.011 kWh/m3 (Crone et al, 2016). Obviously, (0.041 kWh/ m3) × (0.99 kg CO e/kWh) = 40.6 g without the consideration of these factors, the energy- CO /m3, with coal as the fuel for electrical energy based assessment as currently reported in the literature, to production. On the other hand, the residual dissolved a great extent, is misleading. methane after recovery eventually resulted in a direct As illustrated in Fig. 1, a multiple-dimensional carbon emission of (1.71 g/m3)×84 =144 g CO e/m3. As assessment framework of techniques for dissolved such, the overall carbon emission associated with methane recovery should be exercised. For example, dissolved methane after recovery could be determined to compared to membrane contactors, mechanical degasser be 185 g CO e/m3 wastewater treated which was only would not reach the energy-neutral recovery of dissolved about 13% of that in the scenario of the business-as-usual methane, but it has the advantages of chemical-free, (i.e. without dissolved methane recovery: 17.1 g/m3 × 84 simple structure, very low capital investment and =1436 g CO e/m3). operation cost with a smaller footprint. Lastly, it should In another study by Li et al. (2019), an omniphobic be noted that the dissolved methane recovery technologies membrane process was proposed for harvesting dissolved are still at the infant stage, further research is needed to make them more technologically feasible, economically methane from anaerobic effluent with a saturated viable and environmentally sustainable. dissolved methane concentration of 16.4 g/m3 at 35°C. Approximately 0.04 MJ/m3 of energy was needed for achieving recovery efficiencies beyond 90%, equivalent to 0.01 kWh/m3, which was close to the theoretical value reported for membrane-based methane recovery (Crone et al., 2017; Velasco et al., 2021). In this case, the energy recovered from dissolved methane could easily offset the processing energy, i.e. a net energy gain of (16.4 g/m3) × 90%/ (16 g/mol) × 22.4 L/mol × 37.8 MJ/m3 × 35%/(3.6 MJ/kWh)–0.01 kWh/m3 = 0.066 kWh/m3, which was equivalent to a carbon offsetting of (0.066 kWh/m3) × (0.99 kg CO e/kWh) = 65.3 g CO e/m3. However, the 2 2 residual methane after 90% of recovery could contribute to (1.64 g/m3) × 84 = 138 g CO e/m3, suggesting a net methane-associated carbon emission of 72.7 CO e/m3 which was only about 5.3% of that in the case where Fig. 1 Multi-dimensional assessment of techniques for dissolved dissolved methane recovery was not practiced (i.e. methane recovery methods. 16.4 g/m3 × 84 = 1378 g CO e/m3). In addition, methane solubility is inversely related to effluent temperature, Open Access This article is licensed under a Creative Commons indicating that the methane recovery would be more Attribution 4.0 International License, which permits use, sharing, necessary at lower temperature. adaptation, distribution and reproduction in any medium or format, as long It should be realized that chemicals are generally as you give appropriate credit to the original author(s) and the source, required during membrane degassing, e.g. alkaline in the provide a link to the Creative Commons licence, and indicate if changes omniphobic membrane process (Li et al., 2019), and the were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated potential increases in the capital and operation costs otherwise in a credit line to the material. If material is not included in the associated with membrane degassing should also article’s Creative Commons licence and your intended use is not permitted be taken into a serious account in assessing the environ- by statutory regulation or exceeds the permitted use, you will need to obtain mental sustainability and economic viability. In fact, the permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. dissolved methane recovery rate of membrane contactors had been reported to be 0.05 mol methane/(m2·h) (i.e. 0.8 g methane/(m2·h)) at a recovery efficiency of 96% (Velasco et al., 2021). For a middle-sized anaerobic References process treating 200,000 m3/d of municipal wastewater Crone B C, Garland J L, Sorial G A, Vane L M (2016). Significance of with a 21 g/m3 dissolved methane at 25°C, the membranes needed for dissovled methane recovery would be dissolved methane in effluents of anaerobically treated low strength Xiaoyuan Zhang et al. Dissolved methane in anaerobic effluent: Emission or recovery? 3 wastewater and potential for recovery as an energy product: A of hollow fiber membrane contactors for recovery of dissolve review. Water Research, 104: 520–531 methane from anaerobic membrane bioreactor effluent. Journal of Gu J, Xu G, Liu Y (2017). An integrated AMBBR and IFAS-SBR Membrane Science, 554: 184–194 process for municipal wastewater treatment towards enhanced energy U.S. Energy Information Administration (2020). How much carbon recovery, reduced energy consumption and sludge production. dioxide is produced per kilowatt-hour of U.S. electricity generation? Water Research, 110: 262–269 Availiable onine at https://www.eia.gov/tools/faqs/faq.php?id=74 Li X, Dutta A, Dong Q, Rollings-Scattergood S, Lee J (2019). &t=11 Dissolved methane harvesting using omniphobic membranes for Velasco P, Jegatheesan V, Thangavadivel K, Othman M, Zhang Y anaerobically treated wastewaters. Environmental Science & Techno- (2021). A focused review on membrane contactors for the recovery logy Letters, 6(4): 228–234 of dissolved methane from anaerobic membrane bioreactor Liu Y, Gu J, Zhang M (2019). AB processes: Towards Energy Self- (AnMBR) effluents. Chemosphere, 278: 130448 sufficient Municipal Wastewater Treatment. London: IWA Publishing Zhang X, Gu J, Liu Y (2022). Necessity of direct energy and ammonium Liu Z H, Yin H, Dang Z, Liu Y (2014). Dissolved methane: A hurdle recovery for carbon neutral municipal wastewater reclamation in for anaerobic treatment of municipal wastewater. Environmental an innovative anaerobic MBR-biochar adsorption-reverse osmosis Science & Technology, 48(2): 889–890 Rongwong W, Goh K, Bae T H (2018). Energy analysis and optimization process. Water Research, 211: 118058
Frontiers of Environmental Science & Engineering – Springer Journals
Published: Apr 1, 2022
Keywords: Anaerobic treatment; Municipal wastewater; Dissolved methane; Methane recovery; Carbon emission
Access the full text.
Sign up today, get DeepDyve free for 14 days.