The article presents the research results of anaerobic digestion processes in bioreactors of composite mixtures based on initial and residual biomass of Lemna minor duckweed and additives: inoculum (manure), food waste, and spent sorbents to determine biogas potential (biogas volume, methane content). Duckweed Lemna minor, which is widespread in freshwater reservoirs, is one of the promising aquatic vegetation species for energy use. Residual biomass is obtained by chemically extracting valuable components from the primary product. The purpose of the research was to evaluate the possibility of the energy potential of residual biomass of Lemna minor to reduce the consumption of fossil fuels and reduce greenhouse gas emissions. This is in line with the International Energy Agency (IEA) scenarios for the reduction of environmental impact. The obtained results confirm the feasibility of using this type of waste for biogas/biomethane production. The recommendations on the optimal composition of the mixture based on the residual biomass of Lemna minor, which will allow for an increase in biogas production, are given. The obtained data can be used in the design of bioreactors.

The production of low-carbon hydrogen based on renewable energy sources is considered a promising direction in the development of the modern world economy. The purpose of the presented research is to develop technologies and study the processes of converting biogases into hydrogen, as well as its use in low-temperature fuel cells. The methodology for organizing a multi-stage laboratory experiment for obtaining biogas, its purification from impurities and, in the future, the production of biohydrogen was developed based on field studies in Peter the Great St. Petersburg Polytechnic University. The results of modeling studies have shown that during biogas reforming, it is possible to obtain a hydrogen mixture with a hydrogen content of 98% vol and methane 2% vol. Based on the results of the research, the possibility of using the significant potential of “weak” biogas containing methane 30–45% vol to produce biohydrogen (more than 93% vol) was proved. A technique for using biohydrogen in low-temperature fuel cells for energy generation has been substantiated and tested.