Carbon capture and utilization (CCU) covers an array of technologies for valorizing carbon dioxide (CO₂). To date, most mature CCU technology conducted with capture agents operates against the CO₂ gradient to desorb CO₂ from capture agents, exhibiting high energy penalties and thermal degradation due to the requirement for thermal swings. This Perspective presents a concept of Bio-Integrated Carbon Capture and Utilization (BICCU), which utilizes methanogens for integrated release and conversion of CO₂ captured with capture agents. BICCU hereby substitutes the energy-intensive desorption with microbial conversion of captured CO₂ by the methanogenic CO₂-reduction pathway, utilizing green hydrogen to generate non-fossil methane.

Wheat straw without pre-treatment is only converted to methane to a low degree during anaerobic digestion for fuel production due to its low hydrolysis. Current pre-treatment technologies are challenged by high expenses to energy or chemical agents. We examined the low-tech co-ensiling pre-treatment as an alternative pre-treatment of wheat straw, and compared the results with hydrothermal, chemical and mechanical pre-treatment methods. The effects of co-ensiling duration and the mixing ratio between straw and sugar beet root on the methane yields, surface morphology and chemical composition were examined. It was found that co-ensiling could improve production of methane by 34.7%, while a combined hydrothermal and chemical pre-treatment could increase the production of methane by 25.4%. The study demonstrated that the effect of co-ensiling could overlap with hydrothermal and chemical pre-treatment by having similar effects to increase lignocellulosic hydrolysis and improve methane production.

Biomethanation is an emerging Power-to-X technology enabling CO₂ valorisation to produce biomethane using renewable H₂. A promising reactor for facilitating biomethanation is the trickle bed reactor (TBR), however, these bioreactors are conventionally operated with a black-box approach, where the system is solely described by the input and output characteristics. This study employed a novel approach for process surveillance of internal dynamics in TBRs by installing multiple H₂ microsensors along its vertical axis. The H₂ microsensor monitoring was demonstrated for 135 days in a TBR integrated into a full-scale biogas plant. Despite achieving an overall CH₄ productivity of 12.6 L L^-1 d^-1, the vertical positioning of microsensors revealed a clear zonation with CH₄ productivity zones reaching 54.8 L L^-1 d^-1 and enabled early warning detection of deteriorating process performance days before detecting it in the product gas. Thus, vertically positioned microsensors present a promising solution for securing process stability.

The global consensus for decarbonization is accelerating the shift from a linear fossil-based carbon economy to a sustainable circular model in which CO2 becomes a central carbon resource. Carbon capture and utilization (CCU) technologies are essential to recycle CO2, but the high oxidation number and thermodynamic stability of CO2 restrict most conversion technologies to highly concentrated CO2, imposing large energy penalties for concentrating CO2 using solvent-based capture pathways. Bio-integrated carbon capture and utilization (BICCU) is a promising technology that alleviates this energy penalty by merging capture agent based CO2 capture with simultaneous bio-mediated desorption and conversion in a single bioreactor, enabling cost-effective utilization of diluted CO2 sources. However, the direct coupling of CO2 desorption from capture agents and microbial conversion creates new bioreactor design requirements, which must handle the heterogeneous conditions imposed by the presence of capture agents (methyldiethanolamine), dynamic pH shifts driven by CO2 conversion (7.5–9.2), H2 gas-liquid mass transfer rate limitations, residual dissolved oxygen (0–5 mg L-1), and biologically active conversion zones. Addressing these constraints through dedicated bioreactor research, it was discovered that gas-phase trickle bed reactors were an effective platform for combined CO2 desorption and conversion, in contrast to classical bubble column bioreactor designs. This reactor design was tested in a first-of-its-kind full BICCU process chain, including biofuel combustion, flue gas CO2 capture, and bio-mediated CO2 desorption and conversion into renewable e-methane, reaching a CH4 productivity of 8 L L-1 d-1 on par with more mature biomethanation using O2-free concentrated CO2 streams.