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.