ANALYSIS OF NEW FEEDSTOCK TYPES FOR BIOMETHANE PRODUCTION IN UKRAINE

56 Journal of science. Lyon №71/2025 TECHNICAL SCIENCES ANALYSIS OF NEW FEEDSTOCK TYPES FOR BIOMETHANE PRODUCTION IN UKRAINE Zheliezna T. Institute of Engineering Thermophysics of the National Academy of Sciences Ukraine 03057, Marii Kapnist Street, 2a, Kyiv https://doi.org/10.5281/zenodo.17533500 Abstract The purpose of the article is to consider and estimate the feasibility and sustainability of intermediate crops and lignocellulosic biomass as new feedstocks for biogas and biomethane production in Ukraine. Bioenergy plays a significant role in Ukraine’s renewable energy sector, with biogas and biomethane now being priority directions for further development. The search for new types of sustainable feedstock has led to studying intermediate crops and lignocellulosic biomass as prospective sources of biomass with a low carbon footprint and a large potential for energy production. The potential for growing intermediate crops in Ukraine is about 9 bcm/y recalculated into biomethane production. In addition, approximately 3 bcm/y can be obtained from lignocellulosic crop residues. Biomethane projects can be profitable and attractive to investors, with a simple payback period of less than 6 years and an internal return rate of about 20%. These results relate to the case of biomethane and liquefied carbon dioxide being target products. The profitability of biomethane projects depends mainly on biomethane sale price. In the case of co-digestion cover crops or lignocellulosic biomass with manure, carbon footprints of the projects may be negative, which gives an opportunity to charge a high enough biomethane price. Keywords: biomass, biogas, biomethane, intermediate crops, lignocellulosic biomass. Introduction. Having begun its rapid development after the 1970s oil crisis, bioenergy has now become a major sector of renewable energy worldwide. The main advantages of bioenergy are its flexibility regarding the conversion technologies, feedstocks, final products, and the directions of their use (Kirkels 2012). The contribution of biomass is 96% (1.28 EJ/y) to the global renewable heat production, 8% (697 TWh/y) to the global renewable power generation, and more than 51% to the consumption of the alternative to diesel and gasoline energy carriers in road transport (2022-2023) (WBA 2024). In the EU, the share of bioenergy in the final energy consumption is nearly 13%. This allows avoiding 300 Mt СО2е of greenhouse gas (GHG) emissions yearly. Biomass remains the largest renewable energy source in the EU, accounting for approximately 55% of the total renewable energy production. Earlier, this share was about 70%, and its gradual decrease relates to the active development of wind energy, solar energy, and heat pumps in Europe (Zheliezna 2025). Despite quite successful and dynamic development of the European bioenergy sector, there is an opinion that it requires a clearer strategy towards 2050 as well as a clearer and more harmonised definition of “sustainable bioenergy” (Wu 2023). The latter is very important for involving new untapped biomass types in the bioenergy feedstock base. One of the main current trends in the EU bioenergy is the increasing production and consumption of biomethane. This includes, among others, the deployment of biomethane in both compressed (bio-CNG) and liquified (bio-LNG) forms. Biomethane is obtained through biogas upgrading, which involves removing impurities such as carbon dioxide CO2 and hydrogen sulphide H2S. Biomethane provides a sustainable and cost-competitive substitute for fossil fuels, representing one of the few readily available alternatives to fossil fuels for long-distance and energy-intensive transportation segments. Europe is the world’s leading producer of biogas and biomethane, with a continuing increase in bio-CNG and bio-LNG production for transport (EBA 2020; Prussi 2021). The application of biomethane to replace fossil fuels requires minimal additional resources and time to develop new infrastructure or adjust the existing one. This makes biomethane a key player in the transition towards a climate-neutral economy. Decarbonisation of the economy, green transition, and energy security are also key points of Ukraine’s energy policy. Bioenergy plays a significant part in Ukraine’s renewable energy sector. Based on the available biomass potential and conversion technologies, bioenergy contributes to replacing expensive fossil fuels, reducing GHG emissions, and enhancing the energy security of the country. According to the last published Energy Balance of Ukraine for 2020, the share of renewable energy in the total primary energy supply was 6.6%, including nearly 5% (4241 ktoe) of the energy from biomass. In the period of 2010-2020, the production of solid, liquid, and gaseous biofuels increased from 1,458 ktoe/y to 4,438 ktoe/y, with an average annual growth rate of approximately 11%. The production of biofuels in the amount of 4,438 ktoe/y is equivalent to replacing more than 5.2 billion cubic meters per year (bcm/y) of natural gas, which was approximately 17% of Ukraine's total natural gas consumption in 2020. Energy balance for 2021 and later years has not been published due to the martial law in the country. Biogas and biomethane are now priority sectors in Ukraine’s bioenergy. As a direct substitute for natural gas, biomethane can contribute to enhancing energy security and increasing independence from fossil fuels. Journal of science. Lyon №71/2025 57 The search for new types of sustainable feedstock for biogas/biomethane has led to studying intermediate crops and lignocellulosic biomass as prospective sources of biomass with a low carbon footprint and a large potential for energy production (Zheliezna 2024, Geletukha 2025). Thus, the objectives of the study are to analyse the recent dynamics of bioenergy potential and its use in Ukraine, as well as to assess and estimate the feasibility and sustainability of intermediate crops and lignocellulosic biomass as feedstocks for biogas/biomethane. Sequential cropping, which includes cultivating intermediate (cover) crops, gives a considerable opportunity to produce sustainable biomass feedstock for energy. One of the promising directions is to obtain biogas and biomethane. Until now, cover crops have been grown in limited areas in Ukraine to be used as organic fertilizer or feed for animals. The expansion of area under such crops and their integration into biomethane value chains, with nutrients returned to the soil through digestate, could be a new perspective for sustainable bioenergy and agriculture in the country. The introduction of scientifically grounded crop rotations that include intermediate crops, in combination with modern methods for soil treatment and fertilization, makes it possible to use agricultural land more efficiently, improve soil fertility, and maintain proper physical properties of soil. The use of intermediate crops for biomethane is an innovative approach at the intersection of agriculture and energy. Its practical implementation in Ukraine requires a thorough analysis of the economic potential, feasible options, and existing drivers and barriers. This bioenergy direction should be gradually developed using the Biogasdoneright™ model and considering the scalability lessons learned, as was the case in Italy and France (Magnolo 2021). According to Biogasdoneright™, in crop rotation, main agricultural crops should be used only for food or feed, while the biomass of intermediate (cover) crops may be consumed as feedstock for biogas/biomethane, with digestate returned to the field as organic fertilizer (Dale 2016, Selvaggi 2018). Inclusion of lignocellulosic biomass, such as primary agricultural residues, in the feedstock base for biogas/biomethane is another possible way to increase biomass potential for energy. However, effective anaerobic digestion of such biomass requires respective pretreatment, which can be rather intense. The main purpose of pre-treatment is to break the complex structure of lignocellulose to provide access to cellulose and hemicellulose, which are subsequently converted into simple sugars through enzymatic or acid saccharification. Lignocellulosic biomass of agricultural origin includes cereal, grain, and oil crop residues. For Ukraine, the most typical and widely available lignocellulosic crop residues are wheat, barley, rapeseed, and soybean straw; stalks and cobs of maize; stalks and heads of sunflower (Kucheruk 2025a). Methodology. The economic potential of biomass (BM) for energy is calculated as a share of the theoretical potential according to a methodology developed by the Bioenergy Association of Ukraine (Geletukha 2023). The most crucial issue usually relates to primary agricultural residues, as they have many directions of usage, including agriculture itself. The core concept is that the annual amount of each crop residue type (the theoretical potential) is divided between existing (not for energy) and possible (for energy) uses. This division encompasses potential energy production (separately direct combustion and anaerobic digestion), existing agricultural needs (plant cultivation and animal husbandry), and other prospective directions of consumption, while also considering the issue of soil quality maintenance. The latter envisages that some part of crop residues is left on the field as organic fertilizer, and digestate from biogas plants is returned to the field. Along with the digestate, organic carbon (Corg), nitrogen (N), phosphorus (P), and potassium (K) are returned into the soil. The possible shares of each crop residue for different directions of usage are presented in Table 1. For example, straw of spiked grain crops, which is straw of cereals excluding maize, can be sustainably used for energy (20% of the total amount) and for biogas (another 20%). At that, 40% of the straw is left on the field, and 49% in total (calculated by Corg) is returned to the soil. 58 Journal of science. Lyon №71/2025 Table 1. Possible directions of use of agricultural residues. Biomass residue type Energy sector Other uses1) Maintaining soil quality BM left on the field2) BM returned to the field with digestate Total Direct combustion Anaerobic digestion To tal by Сorg by NPK By Сorg by NP K І ІІ ІІІ (I +I I) IV V VI VII VII I (V+ VI) IX (V+ VII) Straw of spiked grain crops 20 20 40 20 40 9 20 49 60 Maize residues 40 30 70 0 30 14 30 44 60 Sunflower residues 40 27 67 0 33 12 27 45 60 Soybean straw 40 30 70 0 30 14 30 44 60 Rapeseed straw 40 30 70 0 30 14 30 44 60 Sugar beet tops 0 90 90 0 10 41 90 51 100 1) Usage as fodder or bedding for animals as well as for growing mushrooms, producing paper, and other. 2) The sum of parts III (energy production), IV (other uses), and V (biomass left on the field) is 100%. Sunflower husk (a secondary agricultural residue) and energy crops can be 100% used for energy. For wood biomass, the share of the theoretical potential available for energy is determined for each biomass type individually, considering accessibility and sustainability issues. For example, at least 20% of felling residues should be left in the forest to maintain biodiversity and soil quality (Nilsson 2016). The shares of other biomass feedstocks available to produce biofuels and biogas/biomethane are determined individually based on factors of sustainability, accessibility, and economic practicability. These shares range from 10% to 100% depending on the biomass type. For example, 10% is applied for maize grain intended for bioethanol production, while 100% is used for intermediate crops as feedstock for biogas. The estimation of the feasibility of projects on biomethane production from intermediate crops and lignocellulosic crop residues is based on a standard techno-economic assessment. This includes determining simple and discounted payback periods, internal return rate, and other essential indexes of economic profitability, as well as carrying out sensitivity analysis. Sustainability of biomass is determined by analysing relevant provisions of Directive (EU) 2018/2001 (RED III) and evaluating biomethane carbon footprints according to “Rules for calculating the greenhouse gas impact of biomass fuels and their fossil fuel comparators” presented in Annex VI of this Directive. Main part. After the beginning of military operations in Ukraine in 2022, the situation in the energy sector has become considerably strained, which has significantly increased the role of biomass fuels in energy security (Geletukha 2022). Considering the current range of costs in Ukraine’s energy market, solid biomass fuels could compete with most fossil fuels and energy carriers in terms of energy unit cost. At that, agricultural biomass, such as baled straw or maize stalks, is nominally competitive even with the subsidized natural gas for the population, which has the lowest cost of energy among the fossil fuels now. As for wood chips, even though their energy cost may be equal to that of gas for the population, they cannot replace subsidized gas, as biomass boilers are on average three times more expensive than gas boilers. Because of this, the difference in energy unit cost for the feasible replacement must be at least twice in favour of biomass. As for biomethane of domestic production, it is now more expensive than natural gas for all types of consumers in Ukraine, as well as the imported natural gas. At present, biomethane produced in Ukraine is exported to the EU. Finding the balance between biomethane export to the EU and domestic consumption requires a comprehensive analysis and elaboration of the state strategy (Zamula 2025). One of the important preconditions for bioenergy development is the availability of biomass for energy production. The economic potential of biomass in Ukraine is assessed, on average, as ~30 Mtoe/y (Table 2), ranging from nearly 34 Mtoe/y in 2021 (the last prewar year) to about 29 Mtoe/y in 2024. The assessment considers other possible or necessary directions of biomass usage, for example, maintaining the soil organic matter in the case of agricultural residues. In addition, it is assumed that digestate from biogas plants is returned to the fields from which the crop residues were taken as feedstock for biogas/biomethane (Geletukha 2023). The total potential consists of three components: solid biomass intended for thermochemical conversion, Journal of science. Lyon №71/2025 59 such as combustion, and biomass allocated to produce liquid biofuels as well as biogas/biomethane. Table 2. Biomass for energy potential in Ukraine. Type of biomass/biofuel Economic potential of biomass Share of the theoretical potential Mtoe/y 2021 2023 2024 SOLID BIOMASS: Agricultural residues: 10.80 8.23 7.43 straw of spiked grain crops 20% 2.87 1.89 1.94 straw of rapeseed 40% 0.80 1.14 0.98 residues of grain maize production 40% 4.18 3.08 2.67 residues of sunflower production 40% 1.79 1.39 1.19 sunflower husk 100% 1.16 0.72 0.65 Wood biomass: 2.70 2.65 2.57 firewood, felling residues, wood processing residues 95% 1.68 1.64 1.56 deadwood, wood from forest shelter belts, residues of pruning and uprooting of agricultural plantations 45% 1.02 1.00 1.01 Energy crops (willow, poplar, miscanthus on 0.5 Mha) 100% 2.58 2.58 2.58 Solid biomass, total 16.08 13.45 12.58 LIQUID BIOFUELS: Biodiesel from agricultural rapeseed 70% (2021)*; 50% (2023, 2024)* 0.57 0.58 0.70 Biodiesel from oilseed energy crops (0.5 Mha) 100% 0.28 0.28 0.28 Bioethanol from agricultural maize 10% 0.86 0.63 0.55 Bioethanol from molasses 75% 0.06 0.07 0.07 Liquid biofuels, total 1.77 1.56 1.59 BIOGAS FROM DIFFERENT FEEDSTOCKS: Manure of livestock and poultry 80% 0.71 0.67 0.65 Agricultural residues: 3.80 3.03 2.88 straw of spiked grain crops 20% 1.21 0.78 0.81 residues of grain maize production 30% 1.72 1.26 1.09 residues of sunflower production 27% 0.33 0.26 0.22 soybean straw 30% 0.15 0.21 0.29 rapeseed straw 30% 0.20 0.29 0.25 sugar beet tops 90% 0.18 0.22 0.22 By-products of food processing industry 39% 0.56 0.72 0.63 Municipal solid waste 75% 0.45 0.36 0.37 Wastewater sludge from public treatment facilities 100% 0.06 0.05 0.05 Silage of maize as an energy crop (1 Mha) 100% 2.57 2.57 2.57 Intermediate (cover) crops 100% 7.89 7.89 7.89 Biogas, total 16.05 15.28 15.05 TOTAL 33.89 30.30 29.22 * The value depends on the rapeseed exports share from Ukraine to the EU and other countries. The considered solid biomass includes primary and secondary agricultural residues, wood from different sources, and energy crops. Historically, Ukraine has had a well-developed agriculture, so agricultural residues make up a significant part of the biomass potential, 25-30% of the total. The potential of wood biomass is much more limited, as forests cover only about 16% of Ukraine’s territory. There are up to 4 million hectares (Mha) of underutilized agricultural land in the 60 Journal of science. Lyon №71/2025 country, which can be used for growing energy crops for solid biomass fuel (~0.5 Mha) and for biogas (~1.0 Mha). The most suitable energy crops are willow, poplar, miscanthus for solid biomass, and maize (silage) for biogas. Liquid biofuels mostly include I-generation biodiesel and bioethanol, making up a minor share of the total biomass potential. On the contrary, the potential for biogas production is considerable (about 50% of the total), covering a wide range of possible feedstocks, including intermediate crops and lignocellulosic agricultural residues. In the future, the potential of biomass for energy may increase due to higher yields of agricultural crops, higher levels of felling in forests, larger areas under energy crops, and involvement of new types of biomass feedstock. An advantage of intermediate crops and lignocellulosic agricultural residues is that they are considered sustainable feedstocks according to provisions of Directive (EU) 2018/2001 (RED III). Directive RED III excludes intermediate (cover) crops from food and feed crops if their use does not lead to demand for additional lands and if the content of organic matter in the soil is maintained. This is the case with bioenergy, which is verified by various certification schemes as required. Many (Launau 2022, Levavasseur 2022, Szerencsits 2015) demonstrate a positive impact on soil due to the return of digestate after digesting the biomass of intermediate crops. Straw, stalks, cobs, and similar agricultural residues are also defined as sustainable biomass by RED III. They are included in Part A of Annex IX, which lists feedstocks for the production of biogas for transport and advanced biofuels. Results of the feasibility study of projects on biomethane production from intermediate crops and lignocellulosic agricultural residues show that such projects can be profitable and attractive to investors, with a simple payback period of less than 6 years and an internal return rate of around 20%. These results relate to the case of biomethane and liquefied carbon dioxide being target products. It is supposed that biomethane is sold in the European market of renewable fuels, while CO2 released during biogas upgrading is liquefied and sold in the domestic market. The projects may have negative carbon footprints reaching -13 g CO2eq/MJ biomethane for intermediate crops as feedstock and -17 g CO2eq/MJ biomethane for lignocellulosic biomass (Geletukha 2025, Kucheruk 2025b). As an example, the main characteristics of a project on biomethane production from intermediate crops are presented in Table 3. It is assumed that two types of cover crops (vetch-oat mixture and winter rye) are codigested with maize silage and pig manure. This feedstock mixture provides a C:N ratio of about 17, which is within the recommended range for effective digestion. Biogas obtained from maize silage is supplied to a cogeneration plant to cover the energy needs of the entire biomethane complex. The main part of biogas is upgraded to biomethane and supplied into Ukraine’s gas transport system. Carbon dioxide released during biogas upgrading is liquified and supplied to a consumer. Digestate from the biogas plant is returned to the fields. Capital costs of the project consist of borrowed funds (60%) and own funds (40%) of the biomethane complex owner, who is also a producer of feedstocks. The described project model is considered optimal to achieve high economic and environmental characteristics of the project. Table 3. Main characteristics of the biomethane project. Parameter Value FEEDSTOCK: Feedstock mixture consumption, kt/y 141.61 Feedstock mixture C:N ratio 16.60 Biogas yield from feedstock mixture, nm3/t dry organic matter 581.30 TARGET PRODUCTS: Biogas production, bcm/y, including: 10.46 biogas supplied to cogeneration plant 2.76 biogas supplied for upgrading 7.70 Biomethane production, bcm CH4/y 5.91 Production of liquefied carbon dioxide, kt/y 5.62 Digestate generation, kt/y 128.25 ENERGY NEEDS OF THE PROJECT: Consumption of electricity, MWh/y 6,386 Consumption of heat, MWh/y 7,485 ECONOMIC INDEXES: Capital costs, million EUR, including: 14.22 machinery and equipment 8.36 construction and assembling 5.04 other 0.82 Operating expenditures, million EUR/y, including: 2.36 feedstock 1.25 operating costs 0.34 logistics of target products 0.46 Journal of science. Lyon №71/2025 61 logistics of feedstocks 0.21 labour cost 0.10 Revenue, million EUR/y (without VAT), including: 4.86 biomethane sale 3.92 liquefied carbon dioxide sale 0.75 digestate sale 0.19 Net present value (NPV), million EUR 5.78 Internal return rate (IRR), % 19.9 Profitability index (PI) 0.41 Simple payback period (SPP), years 5.9 Discounted payback period (DPP), years 7.8 BIOMETHANE CARBON FOOTPRINTS: GHG emission reduction against the fossil comparator of 94 g CO2eq/MJ: winter rye silage 105% vetch-oat mixture silage 102% maize silage 93.5% pig manure 270% Averaged total emission, g CO2eq/MJ biomethane -13 Findings. Analysis shows that at present, only about 10% of the economic potential of biomass in Ukraine is actually utilised for energy, the level of usage being very uneven for different types of biomass. The potential of wood biomass and sunflower husk is utilised at the level of 75-85%, while for primary agricultural residues, this figure is only 1-5%. There are hundreds of straw-fired boilers and heat generators in the country, yet practically no energy installations running on maize or sunflower residues. Based on the available potential and fuel properties, maize stalks are considered one of the most promising types of biomass for energy in Ukraine. Due to the higher ash melting temperature (1100-1200 °C) as compared to straw (800-1000 °C), maize stalks may be used not only in boilers but also in combined heat and power plants and thermal power plants. The major challenge is to provide a moisture content below 35% so that maize stalks can be baled and stored without the biomass worsening in quality. In addition to thermochemical conversion, maize residues can be utilized for biogas production with a potential of 1-1.5 Mtoe/y. However, the biggest source of feedstock for biogas/biomethane in Ukraine is expected to be intermediate (cover) crops. This line of bioenergy development is now being widely studied and analysed. The potential for growing intermediate crops in Ukraine is around 9 bcm/y recalculated into biomethane production. In addition, approximately 3 bcm/y can be obtained from lignocellulosic crop residues. The profitability of biomethane projects mainly depends on biomethane sale price. In the case of codigestion cover crops or lignocellulosic biomass with manure, carbon footprints of the projects may be negative, which gives an opportunity to charge a high enough biomethane price. The sensitivity analysis reveals high dependence on changes in capital costs. A swing up or down of just by 20% might bring the project to the verge of feasibility or, on the contrary, considerably improve its economic indexes. Ukraine has good preconditions for developing biomethane production from intermediate crops and lignocellulosic agricultural residues. It is recommended that studies in these fields be transformed into real projects as soon as possible. References: 1. Dale B.E. et al. 2016. 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