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.

Automated summary

The aim of this study was to increase the yield of biogas and electricity generation by jointly fermenting cattle manure with soap stock obtained from biodiesel production waste. The study determined the biogas yield from cattle manure with the addition of soap stock in a periodic loading mode and developed a mathematical model to predict biogas output in a quasi-continuous loading mode. The research showed that adding soap stock in a periodic loading mode increased the biogas yield by about 2 times, and the optimal soap stock content for a quasi-continuous loading mode was 1.32%. Additionally, using this method reduced the payback period of a biogas plant from 8.7 years to 5.0 years when selling electricity at a feed-in tariff.