Effectiveness of bacterial inoculum as partial substitute for cow dung in the installation and stabilization of biogas plant

Abstract

The prominence of biogas plants for source centric waste management is increasing rapidly. Fresh cow dung is essential for installation of biogas plant. However, its availability is rare in urban areas. In order to help enhance the rate of installation of biogas plants in urban areas, inoculum might be useful. This study aims at developing a bacterial inoculum as a partial substitute for fresh cow dung that sustains the fermenting activity in the biogasdigester. Pure culture of cow dung-derived Bacilli sp. was made and their activity during the initial hydrolysis of organic matter in biogas plant was assessed. The active bacteria, Bacillus subtilis was identified by 16S r-DNA analysis. Dose-activity links of the inoculum under various feedstock combinations of cow dung and vegetable waste were studied based on 60-day biogas yield. Methane level of the 24-hour stock of biogas was sensed indirectly as heat value of combustion captured in 5 litres water. A feedstock combination of 30 kg fresh cow dung, 30 kg vegetable waste and 2.25-liter inoculum when used for installation of 1M3 biogas plant developed stable bacterial consortium in 15-day retention time and performed well on subsequent addition of vegetable waste. The inoculum was effective in the range 25 to 40 ml per kg cow dung-withdrawn. The study showed that cow dung-based biogas installation can be replaced by using one- fourth dung, an equal quantity of organic waste and the bacterial inoculum in the prescribeddose. Keywords: Biogas, Cow dung, Bacillus sp, Inoculum, Hydrolytic retention time.