Anaerobic fermentation of cow manure and wheat straw in low voltage electric field

Abstract

Anaerobic fermentation (AF) is widely implemented technology for energy and organic fertilizer production in more than 50 biogas plants in Latvia. Increasing the efficiency of the anaerobic fermentation process plays an important role in increasing the competitiveness of biogas plants and reducing the state financial support required for the operation of biogas plants. The use of a low-voltage electric field is a promising method for improving the AF process and biogas quality. Experimental investigation of low voltage (0.49-0.75 V) influence on the AF process of cow manure and wheat straw was provided in 16 laboratory bioreactors in volume of 0.75 L in batch mode at temperature 38 ºC. The first group of 7 bioreactors was filled in with inoculums and cow manure and second group of bioreactors was filled in with inoculums and wheat straw. In each group, four bioreactors were arranged with graphite electrodes with wires for connection to a low voltage DC source. Biogas and methane obtainable from inoculums only were investigated in 2 control bioreactors for calculation of biogas obtainable from cow manure and wheat straw only. Anaerobic fermentation process was provided during 68 days until methane emission from bioreactors ceases. Both experimental groups showed an increase in methane production under the influence of a low-voltage electric field. The specific methane production from cow manure increases by 58%, if 0.49 V DC electricity was supplied to bioreactors. The specific methane production from wheat straw decreases by 0.6%, if 0.75 V DC electricity supplied to bioreactors in the second, post-fermentation period only. The effectiveness of usage of the electric field should be investigated further to optimise the electric voltage, form of electrodes and power supply mode.