New study maps pathways to turn biogas waste into profitable products

Biomethane production is expected to expand to meet the growing demand for renewable, secure, and locally available energy sources. Among available production technologies, anaerobic digestion (AD) plays a key role by supporting sustainable development through resource recovery, organic waste management, and biofertilizer production. However, carbon management within AD-based systems can be further improved. During biogas upgrading,biogenic CO₂, which accounts for around 30–50% of the biogas composition, is typically separated and emitted to the atmosphere. Integrating CO₂ utilization alternatives could enhance the system and support defossilization by enabling its direct use or conversion into value-added carbon-based products. Despite this potential, knowledge regarding the feasibility and performance of such alternatives remains limited. This thesis evaluates viable CO₂ utilization alternatives in AD-based biomethane production systems to support decision making, using Sweden as an example. A multi-criteria analysis framework was developed and applied to identify and compare relevant alternatives. Moreover, contextual factors influencing the deployment of CO₂ utilization were examined. In addition, a lifecycle perspective was used to assess the environmental and economic performance of integrating CO₂ utilization alternatives in AD-based biomethane production. The results indicate that methanation, liquefied CO₂, horticulture, and mineral carbonates are the most viable alternatives in the short term comparedto other chemicals and fuels. Nevertheless, low certainty and diverse factors likesensitivity to impurities, energy requirements, potential regulations, andstandards to meet hinder their implementation.Although CO₂ utilization is technically compatible with AD systems,uncertainties related to plant scale, dispersion, and overall system configuration hinder deployment and complicate cost estimations. Favorable market conditions, improved environmental performance, and resource efficiency act as drivers for implementation, whereas uncertain policy landscape, high costs, pricing, market uncertainty, and infrastructure constraints remain key barriers. Compared to carbon capture and storage, feasible CO₂ utilization alternatives can potentially reduce the climate impact while also improving performance in other environmental categories. Among the alternatives, methanation significantly improves climate performance by increasing the biomethane yield but requires low-carbon-intensity electricity for hydrogen production. Furthermore, liquefied CO₂ reduces climate impact mainly by replacing fossil-based CO₂ and does not impose a significant economic burden on biomethane plants. However, it requires additional purification and faces market size constraints. The high concentration of biogenic CO₂ from AD-based biomethane production makes it an attractive resource for utilization. Nevertheless, a systems perspective is essential when assessing its integration. While several utilization alternatives are technically feasible and can potentially improve environmental performance, their implementation depends strongly on technical conditions and broader contextual factors. Clear policy frameworks and targeted market incentives are crucial to accelerate CO₂ utilization deployment.