Carbon capture and utilization has been proposed as an essential climate change mitigation strategy, but only a few implemented cases exist. During biomethane production from anaerobic digestion, CO₂ is commonly separated and emitted into the atmosphere, which can be utilized as raw material for various products. This research aims to identify and assess CO₂ utilization alternatives for possible integration with biogas upgrading from anaerobic digestion by developing a soft multi-criteria analysis (MCA). A literature review complemented with stakeholder participation enabled the identification of relevant alternatives and criteria for assessment. Potential alternatives for CO₂ utilization include methane, mineral carbonates, biomass production, fuels, chemicals, pH control, and liquefied CO₂. Results show that although no alternative performs well in all indicators, there is an opportunity for short-term implementation for methane, biomass production, mineral carbonates, liquefied CO₂, and pH control. Moreover, the uncertainty analysis reveals that even though the technologies have a high technological development, more information on critical aspects is still required. The soft MCA provides information to decision-makers, practitioners, and the academic community on learning opportunities of the alternatives and indicators to step from development into implementation. For instance, the method can be used to assess more specific systems with different locations and scales or to direct efforts to ease the implementation of CCU.

Biogas solutions offer many advantages to improve sustainable development, but there is still untapped potential in its environmental performance. During biogas upgrading, CO2 is separated from the gas to deliver a flow with high methane concentration and thus high energy content. In this practice, CO2 is commonly emitted to the atmosphere without contributing to a net addition of climate gases because of its biological origin, being a missed opportunity for carbon capture. In this paper, CO2 valorization is an option that has been evaluated using a qualitative and quantitative approach, taking Sweden as an example. Results showed that around 140 kt of CO2 can potentially be captured and utilized from biogas upgrading, which can significantly increase in future scenarios. If CO2 were turned into methane using power-to-gas technology, an additional 35% of biogas could be produced in the short term, meaning up to additional 0.7 TWh in 2020. By 2050, around 600 to 1600 kt of CO2 could be available, depending on how well the biogas production develops and how much of the biogas is upgraded, resulting in up to 6.2 TWh of biomethane. The qualitative assessment suggested that only minor modifications in the upgrading process are required for this practice. Biogas actors are interested in getting involved in valorization projects that enhance their circular business and avoid carbon lock-in mainly to improve the environmental performance of biomethane. Moreover, the application of CO2 valorization requires collaboration with different actors to integrate current CO2 demand or innovative transformation technologies.

Utilization of biogenic CO₂ (bio-CO₂) presents a promising strategy to combat climate change while making use of renewable resources. However, it is an early stage market. This study therefore aims to explore the barriers and drivers for bio-CO₂ utilization and their implications for shaping the bio-CO₂ market, using Sweden as an example due to its diverse bio-CO₂ sources and existing initiatives. Twenty-four actors were interviewed, representing different types of market actors, which enabled differences between actors to be identified. For example, producers emphasized economic and market-related barriers, while users addressed uncertainties related to the supply chain and quality requirements. Among the key barriers identified are an uncertain policy landscape, as well as economic and market-related barriers that hinder bio-CO₂ utilization. Improving environmental performance is identified as a key driver for bio-CO₂ utilization but requires overcoming barriers such as high costs and payback requirements to become enacted. Other identified key drivers are the potential for new market opportunities for CO₂, such as e-fuel production, and an increased interest in bio-CO₂ over its fossil-based counterpart. There is a need for a diverse set of actions to support the development of the bio-CO₂ market, such as long-term, stable policies and regulations that support investment and market creation, along with better coordination among governmental organizations. This study thus contributes a holistic perspective on the prerequisites for bio-CO₂ utilization by exploring barriers and drivers for bio-CO₂ from different market actor perspectives and identifying policy implications, using Sweden as a case study. Future research can explore other regions and strategies.

Biomethane production plays a significant role in the bioeconomy and for defossilization. However, the potential of CO2 utilization from biomethane is largely untapped, with only a handful of existing cases in Europe. Diverse applications of CO2 exist, but food-grade liquefied CO2 is usually demanded by the market, requiring biomethane facilities to implement conditioning steps, increasing costs. By applying life cycle assessment and costing, this study identified the effects of introducing food-grade CO2 production in an existing biomethane production plant. Interviews were conducted to assess consumers' willingness to pay for biomethane with lower climate impact. The results showed that when the captured CO2 is used to substitute fossil-based CO2, there is a potential emissions reduction of approximately 220 %. There is also a minor reduction of emissions (around 2 %) with only CO2 capture by reducing the methane slip. Moreover, an increase of around 7 % in costs is expected in biomethane systems producing CO2, without considering potential income from sales. In the studied Swedish context, private actors are willing to pay a higher price for fuel with lower climate impact since it can be used in marketing, while public actors are neutral or negative to a price increase.

In the process of upgrading biogas to biomethane for gas grid injection or use as a vehicle fuel, biogenic carbon dioxide (CO₂) is separated and normally emitted to the atmosphere. Meanwhile, there are a number of ways of utilizing CO₂ to reduce the dependency on fossil carbon sources. This article assesses the climate performance of liquefied biomethane for road transport with different options for utilization or storage of CO₂. The analysis is done from a life cycle perspective, covering the required and avoided processes from biogas production to the end use of biomethane and CO₂. The results show that all of the studied options for CO₂ utilization can improve the climate performance of biomethane, in some cases contributing to negative CO₂ emissions. One of the best options, from a climate impact perspective, is to use the CO₂ internally to produce more methane, although continuous supply of hydrogen from renewable sources can be a challenge. Another option that stands out is concrete curing, where CO₂ can both replace conventional steam curing and be stored for a long time in mineral form. Storing CO₂ in geological formations can also lead to negative CO₂ emissions. However, with such long-term storage solutions, opportunities to recycle biogenic CO₂ are lost, together with the possibility of de-fossilizing processes that require carbon, such as chemical production and horticulture.

Biogas production from waste biomass can create many sustainability-related benefits. However, the CO₂ produced in the process is rarely put to use, although it is often pure and could potentially add value and improve the climate performance if utilized or stored. This study applies life cycle assessment methodology to estimate the overall environmental performance of a biogas system including utilization (CCU) or storage (CCS) of CO₂, comparing six different utilization options and geological storage. The results show that CCU can improve many aspects of the environmental performance of biogas, for example by using CO₂ with renewable hydrogen to produce methane or methanol, as the CO₂ from biogas production can then replace fossil-based processes. Meanwhile, CCS only reduces the climate impact, but increases environmental impact in all other studied categories, as it requires additional processes to treat the CO₂. Utilizing CO₂ from biogas, on the other hand, could be an instrument in the work towards a bioeconomy with reduced fossil resource dependence and improved environmental sustainability. © 2024, ETA-Florence Renewable Energies. All rights reserved.