Biochemical Methane Potential Assessment by Anaerobic Digestion of Locally Available Grasses of Phuentsholing, Bhutan

Abstract

Renewable energy is not only environmental friendly but also promotes sustainable development. Biogas being one of the abundantly used renewable resource, the enhancement and optimization of the yield of biogas can help in reduction of dependence on imported fuel. Biochemical methane potential (BMP) assessment of grass will determine the production of methane (CH4) from this substrate through the process of anaerobic digestion. After determining the parameters such as pH, Biochemical Oxygen Demand (BOD) and Total solids (TS) of three types of local grasses known as Basil, Bermuda and Napier, that affects the production of biogas, Napier grass resulted with the highest potential to produce CH4 gas. Batch and continuous reactor method under mesophilic condition was adopted. The composition of biogas from continuous reactor was obtained using a biogas analyzer (Biogas 5000 Geotech), from which 30.8% of CH4,  8% of CO2 and other inert gases were found. Also, methane to carbon dioxide (CH4: CO2) ratio of 3.81: 1 approximately (80% - 20%) was achieved. Moreover, the batch reactor method showed that 1L Napier grass silage would yield 0.81L of biogas. The concentration of CH4 gas from Napier grass in hydraulic retention time as short as 20 days was very significant. This study shows that Napier grass can be used as an alternative sustainable source of energy in the country which can improve resource constraints.