An original digester design is adopted in building a lab scale 20 L biogas plant. The novelty is the digester has a recycling
line apart from other inclusions (inlet, outlet, gasline etc.) including water seal. Initially cow dung (inoculum) was added. After initial
gas production, cow dung in the digester was co digested with food waste. Main ingredients of the food waste included rice, vegetable
peelings, cucumber, bitter gourd etc., This waste had slightly higher solids and volatile solids (9.3% and 94.9%) content compared to cow
dung (8.5% and 93.1%).
The biogas volume was determined by measuring the downward movement of the water line and calculating the volume of the water that
was displaced by gas. The loading rate of the digester in terms of Total solids was 16.6 kg/ (m3
*day). The amount of biogas production
starting from the 16th to the 23rd day was 6.7L. This biogas did not burn. The failure to burn was probably due to low methane and a
high carbon dioxide concentration in the biogas. After the 23rd day 650 mL biogas was ignited using a match stick. The total biogas yield
recorded was 68.50L for a period of 60 days. The lab temperature was between 30- 340C. Maximum microbial counts of 6.21*104
colonies / mL were observed during the peak of biogas production. The phosphate content was recorded 1.027 mg/100g (slurry content)
on the 60th day. The volatile solids finally reduced to 81.66% of total solids. This volatile solids reduction/destruction/ leads to conversion
of biogas. The volume of biogas produced from the amount volatile solids destroyed calculated using the ideal gas law was 51Litres. In
an Indian scenario, food waste can become a good feedstock for biogas production at Indian households instead of going to the dump
yards or being burnt along with plastic/polythene cover. Of the different types of organic wastes available food waste holds highest
potential of economic exploitation as it contains high amount of carbon in the volatile solids that can be converted into biogas. The
widespread implementation of biogas digesters in urban areas would contribute to the solution of the problems of urban sanitation
energy supply and mitigation of green house gases
