Technological Process of Anaerobic Digestion of Cattle Manure in a Bioenergy Plant

Abstract

Anaerobic digestion consists of the biological decomposition of organic waste under anaerobic conditions by various types of microorganisms. The purpose of this study was to evaluate the effect of the fermentation starter of methanogenic bacteria on the anaerobic digestion of cattle manure in a bioenergy plant. The effect of various methods (physical, microbiological and chemical) on the digestion of cattle manure was studied under mesophilic (35°C) and thermophilic (50°C) modes. The results of the study showed that the content of volatile fatty acids and the pH of the medium was in the optimal range, the yield of methane biogas (CH4 ) during anaerobic digestion at 35°C was 0.45 m3 /kg and at 50°C was 0.58 m3 /kg. The data obtained indicate that the thermophilic mode (50°C) of anaerobic digestion of manure effectively affects the yield of methane biogas. Based on anaerobic digestion in mesophilic mode, a fermentation starter of methanogenic cultures adapted to thermophilic conditions was obtained. According to cultural and morphological characteristics, the cultures were assigned to the genera Methanopyrus and Methanococcus. The results of a study on the effect of the fermentation starter of methanogenic bacteria in fermented manure at 50°C showed that with an increase in the dose of the fermentation starter, the methane-forming ability of anaerobic bacteria increased and the process of methane biogas release intensified (from 0.36 m3 /kg to 0.79 m3 /kg). Besides, the dose of methanogenic fermentation starter based on Methanopyrus and Methanococcus isolates (28 kg) was determined. When the bioenergy plant is launched in thermophilic mode, the release of biogas increases by 2.2 times, and the digestion period decreases to 10 days.