Abstract
Biological methanation as a method of sector coupling between electric and gas grids is expected to be an integral part of the green energy change. Wastewater treatment plants (WWTPs) involving anaerobic digestion (AD) allow existing infrastructure to operate as energy conversion plants, to close carbon cycles and to generate long-term storable energy in the form of biomethane. Therefore, municipal raw sludge and additional organic residuals (co-substrates) are converted into biogas. Hydrogen is added to convert the carbon dioxide in the biogas into methane via biological methanation (BM). In this study, the energy amount that is convertible via BM in municipal digesters in Austria was calculated. The amount of energy, which can be transformed from electric surplus energy into biomethane, was assessed. Operational data from lab-scale digesters were combined with data from 28 Austrian full-scale wastewater treatment plants with AD. They represent 9.2 Mio population equivalents (PE), or 68% of Austria’s municipal AD capacity for WWTPs > 50,000 PE (in sum, 13.6 Mio PE). Energy flows for BM including water electrolysis and anaerobic digestion were created on a countrywide basis. It was found that 2.9–4.4% (220–327 GWh·y−1) of Austria’s yearly renewable electricity production (7470 GWh·y−1) can be transformed into biomethane via BM in municipal digesters.
Highlights
The share of fluctuating renewable energy sources, such as wind and photovoltaics, is increasing worldwide
Wastewater treatment plants (WWTPs) involving anaerobic digestion (AD) allow existing infrastructure to operate as energy conversion plants, to close carbon cycles and to generate long-term storable energy in the form of biomethane
Energy flows for biological methanation (BM) including water electrolysis and anaerobic digestion were created on a countrywide basis
Summary
The share of fluctuating renewable energy sources, such as wind and photovoltaics, is increasing worldwide. In Austria, the number of wind turbines doubled within 7 years (from 2011 to 2018) from 662 to 1313, while the installed electrical power increased from 1099 to 3045 MW [1]. In the eastern part of Austria, large numbers of wind turbines have been installed (Lower Austria 729 and Burgenland 429). To reach a fully renewable electricity supply, further systems are needed. With an increasing share of fluctuating renewable energy production, network stabilization and long-term energy storage are urgently needed. Resch et al [4] reported that the storage capacity in hydropower plants in Austria is almost fully exploited, and this capacity is needed for medium-term energy storage from days up to weeks. The existing natural gas infrastructure could be utilized for long-term or seasonal storage ranging from weeks up to months
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