Biomethanization of mixed organic substances is the effect of coexistence of numerous groups of microorganisms. Methanogenic degradation of such substances involves at least three different trophic groups of anaerobes, namely fermentative heterotrophs, proton-reducing syntrophs and methanogenic archaea. The development of molecular techniques allowed to detect some new groups of bacteria and archea, which often stay unculturable. The cultivation of uncultured organisms is of great significance in recognizing the function of these organisms. In the past few years, newly discovered microorganisms have been successfully isolated from anaerobic sludges, and the information regarding their physiology in connection with phylogeny is updated regularly.

Biogas production has a big potential to provide clean energy. To evaluate the future production and maturity of biogas technology the generalized Weng model was proved to be effective, due to it has the minimum error. The simple algorithms to determine its parameters have been proposed. The simulation results for China, USA, and EU have been presented. The quantity and quality analysis for biogas feedstock has been carried out. Energy Return on Energy Invested (EROEI) indicator for different biofuels was considered. According to analysis done biogas from maize residue and chicken manure has high EROEI. Shannon Index was suggested to evaluate the diversity of feedstock supply. Biomass energy cost indicator was grounded to be used for feedstock energy and cost assessment. Biogas utilization pathways have been shown. Biogas boilers and CHP have the highest thermal efficiency, but biogas (biomethane) has the highest potential to earn as a petrol substitute. Utilization of biogas upgrading by-product (carbon dioxide) enhances profitability of biogas projects. Methods to assess the optimal pathways have been described.

The necessity of developing the production of biogas and digestate at Ukrainian sugar factories focused on the further sale of biomethane in the energy market and for its own needs is substantiated, which will partially ensure the energy security of the state under martial law. The volumes of sugar beet cultivation are determined, and the potential volumes of biogas production from the waste of Ukrainian agro-industrial complexes are investigated. A model of the functioning of a production bioenergy cluster based on a sugar factory has been developed and proposed. As a result of the study, it was found that a tangible way to increase the level of energy autonomy of the processing industry of the agro-industrial complex of Ukraine is the production of biogas by anaerobic digestion and its subsequent purification to the state of biomethane. To produce this type of biofuel, the use by-products of agriculture, agro-industrial processing enterprises, and organic waste from territorial communities where sugar factories are located is advisable. At the same time, as the analysis of resource potential shows, modern methane generation technologies allow using a wide range of biomass as a raw material base, which can be obtained both from production activities (non-core (non-target) products) and from household waste in general, which is one of the methods of solving the problems of their utilization. It has been determined that the use of advanced technologies for the transportation of liquid digestate and its injection will reduce the cost of application, increase the absorption in the soil, and the use of biodiesel will reduce transportation costs.

The paper describes the most important factors controlling the process of methanogenesis in the biomethanization technology. It discusses the operational regimes of temperature as well as pH, C/N ratio, the necessity for micronutrients and sensitivity to a number of toxic compounds. Components with an inhibitory effect are characterized as biostatic compounds (ammonia, VFAs, hydrogen sulfide and salinity-inducing substances) and biocidal substances (such as surfactants and pharmaceuticals). The threshold limits of the compounds in question securing the system against disturbances are introduced, as well as the measures counteracting inhibition. Some ways of overcoming the negative impact of environmental factors on the system are presented, including co-fermentation, supplementation of nutrients, removal of ammonia and hydrogen sulfide by different methods and acclimatization of methanogens to inhibitory substances.

The aim of this paper is to show the basic principles of the anaerobic digestion process. All the stages of degradation, such as hydrolysis, acidogenesis, acetogenesis and methanogenesis are characterized. Biodegradable organic matter consists of three main types of substances: carbohydrates, proteins and lipids; the metabolic pathways of their decomposition are described. The last part of the paper presents the co-digestion process, its benefits and technological parameters required to make that process attractive from an economical and environmental point of view.