Assessment of the Seasonal Potential of Macroalgae and Grass in the Sea of Azov for Methanogenesis and Optimization of the Digestate’s Carbon/Nitrogen Ratio

Large amounts of macroalgae and grass are dumped on the shores of the Sea of Azov in different seasons. Aquatic plant biomass management could contribute to sustainable development. By mixing them with co-substrates in an anaerobic bioreactor, not only can biogas be extracted, but suitable fertilizers can also be obtained. This study discusses the possibility of using methanogenesis waste from Azov Sea algae and sea grass as a fertilizer for agriculture. The main criterion is the presence of carbon (C) and nitrogen (N) in the waste products of methanogenesis. The influence of climatic and seasonal factors in the Azov region on the quality and quantity of storm emissions, on the productivity of methanogenesis, and changes in the ratio of carbon (C) and nitrogen (N) during methanogenesis and in the fermented substrate has been established. The influence of the ratio of the components of the mixture in various proportions, before methanogenesis, on the productivity of methanogenesis and the change in the ratio of carbon (C) and nitrogen (N) during the process of methanogenesis, and in the fermented substrate were studied. The biomass of the Sea of Azov, cattle manure and wastewater waste in various proportions, were used as components of the mixture. Recommendations are given for the selection of mixture components for methanogenesis, with predicted indicators of the ratio of carbon (C) and nitrogen (N) in the fermented substrate.