Integration of Electrochemical cell for Enhancement of Biogas production from cattle manure and molecular characterization of isolated microflora

Abstract

Nepal is a developing country where most of the population is still living in rural areas. A continuous supply of cooking gas as Liquid Petroleum Gas is difficult and expensive. So biogas is a good alternative for them. Biogas production is affected by several factors; temperature is an important factor to be considered during anaerobic digestion (AD) for effective degradation of organic waste. Though most of the rural areas’ of Nepal have assembled biogas plant, due to the climatic variation, during winter season, production of biogas is less. Enhancement of biogas production can be done by various methods. Among them integration of microbial electrochemical cell (MEC) system in existing AD is a new and innovative technique where a small voltage of electricity supplied to reduce CO2

produced in digester to methane with help of methanogens as a biocatalyst. AD using cow dung is cheap and clean method of production of biogas which help to reduce serious environmental and health problems. During this work, integration of microbial electrochemical cell (MEC) system in conventional anaerobic digester showed reduction percentage was 2.7% and 8% greater in 1 L and 5 L digester respectively in MEC compared to conventional control setup while reduction of soluble reducing sugar was 33% and 9% greater in 1 L and 5 L digester at 15°C compared to control setup. At room temperature (23-29°C), reduction percentage of COD was about 11% and 18% higher in comparison to controlled digester. Likewise, reduction percentage of soluble reducing sugar was 32% higher in 1L and 19% higher in 5 L digester compared to the control digester. Biogas production was enhanced by about 28% compared to control setup even at temperature of 15°C in both 1 L and 5 L digester. Similarly, enhancement of biogas in 1 L digester and 5 L digester was 35.18±0.52% and 41.17% respectively at room temperature. Despite of enhancement, the reaction of microbial electrochemical cell was done successfully for short period of time which is not enough for complete digestion of cow dung. Hence, further study on the MEC for elongated digestion of organic waste and assembly of fed batch system is necessary. We analyze the change in different parameters for already existing 6000 L biogas plant. There was very negligible change in COD, soluble reducing sugar as there was a provision of continuous feeding of substrate every day. For the identification of microorganism, among six isolates 14IN and 18IN showed significant level of cellulase production while doing hallo zone test with congo red. PCR product of 16s rRNA of while sequenceing showed the microorganisms 14IN and 18IN were Bacillus licheniformis and Bacillus aerius respectively. Keywords: Biogas, microbial electrochemical cell, anaerobic digestion, chemical oxygen demand.