Filters
Using soap waste from biodiesel production to intensify biogas generation during anaerobic digestion of cow dung
The aim of the work is to increase the yield of biogas and the generation of electricity at biogas plants due to the joint fermentation of cattle manure with the addition of soap stock obtained from soap waste from biodiesel production. To achieve this goal, the following tasks were solved: the yield of biogas from cattle manure was determined with the addition of soap stock for a periodic mode of loading the substrate, taking into account the data obtained, a mathematical model of biogas output for a quasi-continuous mode of loading the substrate into the digester was developed and its adequacy was confirmed. The novelty of the work lies in the fact that according to the data of experimental studies of biogas yield at a periodic loading mode using this model, it is possible to predict the maximum biogas yield for a quasi-continuous mode of loading the digester. The significance of the research results lies in the fact that when soap stock is added to the substrate with a periodic mode of loading the digester, a general increase in the biogas yield without diauxy is observed by about 2 times. The optimal content of soap stock in the substrate for a quasi-continuous mode of loading the digester, at which the biogas yield will be maximum, is 1.32%. When electricity is sold at a feed-in tariff, the payback period of a biogas plant is reduced from 8.7 years to 5.0 years.
Biogas Plant Operation: Digestate as the Valuable Product
Fertilization is an essential element in plant cultivation. Supplying the right amounts of nutrients allows plants to grow and develop. Due to the rising price of mineral fertilizers, other fertilizers and soil conditioners are growing in importance. One of these is the digestate produced in agricultural biogas plants. Due to its properties, the digestate can be used directly as a fertilizer. In this case, the effects of application can both change the soil environment and directly affect plant growth. Physical, biological, and thermal transformations can also produce products based on the digestate or its fractions, which can be successfully used for fertilizer purposes. Among other things, this paper discusses the production and use of composts, biocarbon, and/or fertilizer granules from the solid fraction of the digestate. Numerous scientific studies, including the authors’ own research in this article, indicate that digestate can be successfully used as fertilizer, both without processing and with selected methods of treatment. However, further research is needed—especially on the diversity of raw materials used for biogas production and their effects on the composition and performance of the digestate. In addition, research should continue on the processing of digestate into specific products, depending on the needs of soils and plants.