Sourcing and use of biogenic CO₂ - and associated challenges

Biogenic CO₂ is generated from the harvest, fermentation, processing, decomposition, digestion, or combustion of biomass and biomass-derived products and is part of the natural short carbon cycle that does not contribute to atmospheric CO₂ accumulation. Removing biogenic CO₂ can result in net-negative emissions.

CO₂ capture and removal: fossil emissions vs. biogenic emissions

Natural contributors to biogenic CO₂ include cellular respiration, microbial fermentation and ocean outgassing. Capturing CO₂ from natural sources is not viable without Direct Air Capture (DAC), due to slow processes and low CO₂ volumes. Capturing Biogenic CO2 from industrial processes is possible and is already widely practiced in some industries.

Why is Biogenic CO₂ needed?

Decarbonising the aviation industry is particularly challenging due to its reliance on high-energy-density fuels and the lack of scalable, cost-competitive and sustainable alternatives. As regulatory pressures mount, such as those from the Delegated Act on Renewable Fuels of Non-Biological Origin (RFNBO) and the ReFuelEU Aviation initiative, the focus is increasingly on eSAF.

eSAF is produced by power-to-liquid (PtL), using renewable energy to convert CO₂ (and green H2) into synthetic fuels, ensuring a low carbon footprint over the fuel’s lifecycle. The RFNBO Delegated Act mandates the use of sustainable CO₂ sources indefinitely, with the use of fossil-derived CO₂ sources facing a 2041 deadline. The shift towards sustainable CO₂ sources is essential for meeting stringent eSAF blending quotas, as set by the ReFuelEU Aviation regulation, which starts at 1.2% in 2023 and rises to 35% by 2050. The EUʼs SAF mandate may have set a path in motion beyond its borders, as some countries are now considering policies to mandate e-fuels too (e.g., the UK), or to financially support e-fuels (e.g., the USA and Canada) [1] [2].

Within the PtL route, sourcing CO₂ is a critical factor. Sustainable CO₂ sources include CO₂ from direct air capture (DAC) and biogenic CO₂ from industrial point sources. Until DAC becomes a viable and cost-effective solution, biogenic CO₂ from industrial emitters will be the preferred choice for meeting immediate regulatory and sustainable goals in aviation. However, the availability of biogenic CO₂ is limited and is likely to be a bottleneck for the further scale-up of e-fuel production. Additionally, CO₂ capture challenges and sustainability concerns will further prohibit the current biogenic CO₂ supply to meet the demands of the growing biogenic CO₂ market [3].

According to IEA, the demand for biogenic CO₂ to fuel 10% of maritime and aviation transportation will far exceed biogenic CO₂ supply from low-cost, high-concentration bioethanol sources by 2030

Where does industrial biogenic CO₂ come from?

Capturable biogenic CO₂ is available from some industrial sectors, which emit sufficiently high volumes and concentrations of biogenic CO₂. Around 2.5 million tonnes of biogenic CO₂ is currently captured annually, more than 90% of which comes from bioethanol plants [4]. Five major industries which can be an economically attractive source of Biogenic CO₂ are discussed below.

Summary table of the key characteristics of the industrial sectors, including concentration and typical quantity

¹ Most facilities use fossil fuel sources for some or all of power and heat requirements. Some facilities use integrated on-site combined heat and power (CHP) for some energy demands

² Bioethanol produced from corn or sugar

³ Dependent on ratio of biomass to fossil feedstock

⁴ As classified by EU, although 50% of energy used in Lime kiln comes from the boiler, resulting in a mix of biogenic and anthropogenic CO₂ emissions

⁵ Calculated as weighted average. Emissions vary by pulp and paper grade

Bioethanol

Bioethanol plants generate significant quantities of CO₂ as a by-product of the fermentation process. Monomeric sugars derived from corn or sugarcane (biomass) are fermented to produce ethanol, releasing 99 (mol)% of CO₂ in the process. A possible secondary CO₂ source from on-site CHP production has lower CO₂ concentrations, ranging between 2-5 (mol)%.

Bioethanol production producing high concentration of biogenic CO₂ during fermentation and low concentration CO₂ during on-site CHP

Biogenic CO₂ from bioethanol is currently the most commercially attractive source, as high concentration streams can be captured at low cost but will not be able to meet the high demand as a standalone source.

Biogas

Biogas facilities also produce high concentrations of biogenic CO₂ through the anaerobic digestion of organic waste materials. During this process, microorganisms break down the organic matter, producing biogas consisting of ~50-80 (mol)% CH₄ and ~20-50 (mol)% CO₂ – the exact ratio dependent on feedstock – and a digestate. Biogas can then be combusted in CHP plants or upgraded at Biomethane-to-Grid (BtG) facilities, producing biomethane and a >98% pure biogenic CO₂ stream [5].

Biodegradable non-woody plant or animal waste matter is used to produce biogas

Biogas and biomethane, while currently accounting for a small portion of global energy consumption (<3%), are expected to be the fastest growing form of bioenergy and are predicted to increase their share of the bioenergy demand market to 12% by 2040 [6]. While large corn bioethanol production facilities generate approximately 1 million tonnes of CO₂ annually, large biomethane plants emit less than 5% of this amount each year, providing only enough CO₂ for a 50 MW e-fuels project [3]. Centralised models are becoming an increasingly popular and necessary method to enhance biogas production, biomethane output and biogenic CO₂ quantities, potentially allowing for larger individual e-fuels facilities. However, even if projected expansion is realised, it is unlikely that CO₂ from biogas and biomethane facilities will be a sufficient supplementary source of biogenic CO₂ [5].

Biomass-to-Energy

Large volumes of biogenic CO₂ are emitted from biomass-fired power plants. CO₂ Biomass power plants generate heat or electricity through the combustion of biomass feedstock, producing steam and electricity through a turbine generator.

Biomass-fired power plants typically combust a mixture of woody biomass with coal. The share of biogenic CO₂ in the exhaust gas can range anywhere between 0-100%, depending on the fuel mix

While the volume of flue gas is high, the concentration of CO₂ is significantly lower, ranging between 8-15%, of which the biogenic portion is dependent on the fuel mix. Co-firing of biomass with fossil fuel (mostly coal) is common, typically using 20-50% biomass [7]. Currently, the largest point source of biogenic CO₂ is emitted from the Drax power station, a 100% biomass-fired power plant in the UK. While the volume of CO₂ emitted from biomass-fired power plants sounds promising, the low concentration of CO₂ results in high capture costs.

Pulp and Paper

The Pulp and Paper Industry (PPI), of which Kraft mills are dominant, is another industry with the potential to supplement biogenic CO₂ supply. Substantial amounts of wholly biogenic CO₂ are emitted from the combustion of black liquor in the recovery boiler.

Simplified Kraft mill process, emitting CO₂ from three locations, namely the recovery boiler, power generator boiler and lime kiln

At Kraft mills, the majority of CO₂ emissions (70-75%) come from the recovery boiler and 15-20% originate from the power generator boiler, both sources are biogenic. The remaining 5-15% are emitted from the lime kiln, where the CO₂ emissions are a combination of biogenic and anthropogenic CO₂, as the kiln uses heat from the boilers. GHG emissions vary by pulp and paper grade, ranging from 608 – 1,978 CO₂eq per tonne of product. Fuel usage is the greatest contributor to GHG emissions and is the main target of emission reduction strategies.

Waste-to-Energy

The world generates approximately 2 billion tonnes of Municipal Solid Waste (MSW) per year and this is expected to increase to 3.4 billion tonnes by 2050. Converting waste to energy is one of the most environmentally friendly methods of dealing with residual waste. Most MSW is landfilled (37%) or dumped (33%), with only 11% being currently incinerated. The most common incineration application, processing Municipal Solid Waste (MSW) in a combined heat and power (CHP) plant, delivers approximately 90% of produced energy to the electric grid [8].

Typical WtE plant incinerates a heterogeneous mixture of MSW, producing approximately 50% of biogenic CO₂. This share varies depending on the waste mix. In the EU, for example, this percentage ranges between 53% and 63%

Countries are aiming to reduce MSW disposal in landfills, with incineration being a key solution to not only disposing of increasing quantities of waste, but playing a role in meeting rising energy demands [9].

Other emitters

Other industry emitters of biogenic CO₂ include the cement, timber and alcohol & sugar industries. The cement industry currently accounts for 7% of global CO₂ emissions. However, unless biomass-based fuels are used, CO₂ emissions from the cement plants are anthropogenic. Most alcohol and sugar plants are small scale, with large scale production facilities often producing ethanol. Emissions from the timber industry are primarily from energy consumption and this industry is more suitable for decarbonisation via electrification or in some limited circumstances hydrogen fuel switching. Carbon capture is unlikely to be deployed in the timber industry in the short and medium-term.

Challenges with capturing more biogenic CO₂

Cost of capture

According to our internal database, which tracks global biogenic CO₂ emissions from 2,205 facilities, these five major industries collectively emit around 401 Mtpa annually - enough, in theory, to meet the demands of both the aviation and maritime sectors. High-concentration, low-cost CO₂ sources like bioethanol and biogas alone cannot meet demands, while the low concentration of biogenic CO₂ from other sources result in high capture costs, making them economically challenging.

Total annual emitted volume of CO₂ with associated costs of capture across five industries. The average portion of biogenic vs anthropogenic emitted CO₂ is shown. The shades represent the typical concentration of CO₂ emitted, also shown as a percentage

• Bioethanol: Capturing biogenic CO₂ from fermentation during bioethanol production is the lowest-cost capture application, as it is a pure form of CO₂ requiring only dehydration and compression at $25-35/t CO₂. Capturing CO₂ from power and heat generation at bioethanol facilities is costlier at around $70-85/tonne, with only a small portion being biogenic in nature [10].

• Biogas: Established technologies like membrane and cryogenic separation can separate and capture CO₂ from biogas upgrading facilities. However, capturing CO₂ from CHP flue gas, which typically contains 10% CO₂, has experienced a limited number of pilot and feasibility studies due to low emission volumes. Viable CO₂ capture potential lies in centralised large-scale BtG facilities, where economies of scale can reduce the price gap between natural gas and biomethane.

• Biomass-to-Energy: Similar capture technologies used for coal combustion power plants are suitable for biomass co-firing. Co-firing biomass with coal up to 10% does not require additional investment. However, the higher cost of biomass compared to coal can cause variations in carbon capture costs for applications exceeding 10% [11].

• PPI: Despite the large volumes of emitted CO₂, so far, no pulp and paper mills are equipped with or have announced plans for carbon capture. High estimated capture costs of $70-82/tonne CO₂ make paper and board production economically unfeasible. However, Kraft paper mills, except for lime kiln operations, are energy self-sufficient and heat integration can lower capture costs to $65-85/tonne CO₂, but would still require negative emission credits or other supporting policies to make capturing economically feasible. 

• WtE: Process heat integration and solvent technology innovations can reduce cost of current CO₂ capture technologies, such as amine-based absorption, from $70-85 per tonne of CO₂ to $35-50 per tonne. Although WtE flue gas has a low CO₂ concentration (8-12%), it contains less sulphur and fewer particulates than coal-fired flue gas, simplifying capture and reducing gas cleaning costs. However, WtE plants operate on a smaller scale, emitting smaller CO₂ volumes per facility. Successful carbon capture installations at WtE plants must deliver low-cost abatement without the economies of scale available at larger power plants [12] [13].

  
  

Sustainability challenges

Even if capture cost challenges can be resolved, sustainability concerns, such as biomass sourcing, risk of indirectly promoting deforestation and competition with food resources, must be managed carefully.

For example, in the last 20 years, the Pulp and Paper industry’s energy use has only increased by 1% due to the high share of biomass as feedstock and the use of onsite process by-products. However, the sustainability practices of PPI have been under scrutiny due to its heavy dependence on water, water pollution, intensive use of natural resources, forest degradation, deforestation and waste generation. As fuels are the greatest contributor to GHG emissions, emission reduction strategies focus on improving operational energy efficiencies and switching to renewable energy, as outlined by the US EPA. Strategies focusing on wastewater treatment and on-site landfills will address some sustainability concerns. As the world’s largest user of woody biomass, the PPI must ensure sustainable sourcing practices and promote responsible forest management.

The sustainability and growth potential of biomass-fired power plants also depends on the sustainability and availability of woody biomass resources. Concerns have been reported regarding Drax’s sourcing of mature, rare forest wood from Canada before updating their policies in 2023 [14]. A recent example further demonstrates these issues, where the mandatory co-firing at all coal power stations resulted in the mass deforestation of a large rainforest to meet feedstock demands as Indonesia transitions away from fossil fuels [15].

In addition to the sustainability challenges faced by the PPI and biomass-fired power stations, the bioethanol industry also grapples with sustainability issues related to its feedstock. Currently, 90% of commercial bioethanol facilities use 1st generation feedstock – valuable food resources such as grains and sugars. 2nd generation bioethanol production, which uses non-food biomass, has limited economic viability due to high pretreatment costs. 3rd and 4th generation feedstock, such as algae, show higher yields but are currently technologically immature and face cultivation difficulties. For the immediate future, bioethanol facilities will continue to use valuable food resources as feedstock, which can have negative environmental consequences [16].

In the last 10 years, CO₂ emissions from WtE incinerators have doubled, with over 2,430 WtE plants operating globally. This is projected to increase further as more plants come online. A lot of attention has been directed towards limiting landfill sites in developed countries. However, the share of non-biogenic CO₂ emitted is rising over time. As more paper is being recycled, the portion of plastics and non-biogenic waste in MSW is expected to increase, increasing the net CO₂ emissions from WtE plants. The only way to eliminate net CO₂ emissions from the WtE industry is through CCUS.

The challenges are evident when examining the landscape of projects utilising biogenic CO₂. Despite commitments to produce volumes of e-kerosene potentially exceeding ReFuelEU mandates, most eSAF projects are in the early development stages, facing significant uncertainty. Our database tracks around 40 PtL-to-SAF projects, but many of these, despite their ambition, remain aspirational with no concrete plans for commercial realisation. However, several projects are more advanced than others. No major industrial project has yet to reach a final investment decision (FID). However, four plants are in the late-FEED phase and are hoping to reach FID by end of 2024 and begin production by 2026-2027.

Competition for low-cost biogenic CO₂ is intense, with sectors such as shipping, chemicals, plastics, and construction materials also seeking sustainable CO₂ sources. This competition necessitates technological advancement and policy support not only in CO₂ capture in biogenic CO₂ emitting industries, but also incentivising DAC to partially address biogenic CO₂ deficits.

References:

[1] Directorate-General for Communication, “European Commission,” 12 8 2023. [Online]. Available: https://energy.ec.europa.eu/topics/renewable-energy/renewable-energy-directive-targets-and-rules/renewable-energy-directive_en

[2] Council of the EU, “European Council,” 9 10 2023. [Online]. Available: https://www.consilium.europa.eu/en/press/press-releases/2023/10/09/refueleu-aviation-initiative-council-adopts-new-law-to-decarbonise-the-aviation-sector/

[3] “Why shipping is opting for green hydrogen-based methanol over ammonia, despite much higher fuel costs,” January 2024. [Online]. Available: https://www.hydrogeninsight.com/transport/why-shipping-is-opting-for-green-hydrogen-based-methanol-over-ammonia-despite-much-higher-fuel-costs/2-1-1577939

[4] IEA, “IEA,” 25 May 2024. [Online]. Available: https://www.iea.org/energy-system/carbon-capture-utilisation-and-storage/bioenergy-with-carbon-capture-and-storage.

[5] EBA, “Biogenic CO2 from the Biogas Industry,” September 2022. [Online]. Available: https://www.europeanbiogas.eu/wp-content/uploads/2022/10/Biogenic-CO2-from-the-biogas-industry_Sept2022-1.pdf

[6] IEA, “Outlook for biogas and biomethane: Prospects for organic growth,” IEA Publications, France, 2020

[7] “Biomass with CO2,” 2021. [Online]. Available: https://bellona.org/assets/sites/3/EBTP__ZEP_Report_Bio-CCS_The_Way_Forward.pdf

[8] WtERT, “Global WteRT Council,” 2023. [Online]. Available: https://wtert.org/publications/

[9] “What a waste 2.0: a global snapshot of solid waste management to 2050,” 2018. [Online]. Available: https://documents.worldbank.org/en/publication/documents-reports/documentdetail/697271544470229584/what-a-waste-2-0-a-global-snapshot-of-solid-waste-management-to-2050

[10] “CO2 Capture in a Thermal Power Plant Using Sugarcane Residual Biomass,” Energies: Research Trends and Challenges in Bioenergy with Carbon Capture and Storage, p. https://doi.org/10.3390/en16124570, 2023

[11] IEAGHG, “Further Assessment of Emerging CO2 Capture Technologies,” September 2019. [Online]. Available: https://ieaghg.org/publications/further-assessment-of-emerging-co2-capture-technologies/

[12] “Waste-to-energy and waste-to-hydrogen with CCS: Methodological assessment of pathways to carbon-negative waste treatment from an LCA perspective,” January 2024. [Online]. Available: https://www.sciencedirect.com/science/article/pii/S0956053X23006955?via%3Dihub

[13] Global CCS Institute, “Waste-to-Energy with CCS: A pathway to carbon-negative power generation,” 2019 Perspective , 2019

[14] “Drax: UK power station still burning rare forest wood,” BBC News, 28 February 2024. [Online]. Available: https://www.bbc.co.uk/news/science-environment-68381160

[15] “Frontiers in Energy Research,” 2 July 2021. [Online]. Available: https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2021.684234/full

[16] OECD/FAO, “OECD-FAO Agricultural Outlook 2021-2030,” OECD Publishing , Paris, 2021

[17] CropEnergies, “Magazine for Sustainable Transport,” 2021. [Online]. Available: https://refuel.bio/wie-entsteht-bioethanol/