DETAILED DESIGN OF A FIBER GLASS BASED MEDIUM SCALE PLUG FLOW REACTOR FOR BIOGASIFICATION OF BIODEGRADABLE FOOD WASTE FOR RURAL AND URBAN INDIA

Abstract

Plug flow reactor vessel is a long narrow (typically a 2:1 ratio; 2 times as long as the width) insulated inside and heated tank made of reinforced concrete, steel or fiberglass with a gas tight seal cover to collect the biogas. These digesters operate at a mesophilic or thermophilic temperature range. Retention time is usually ranges between 15 to 20 days. Fiber Glass is the material used for construction of the digester tank. The methanogens (methane producing micro-organisms) can digest sugar, starch, fats, cellulose and proteins etc. Their digestive mechanism is similar to that of many other organisms, up to the point of converting the food into acetic acid. Methanogens convert acetic acid into methane and carbon dioxide. (CH3COOH = CH4+CO2). They work optimally at the temperature of 38°C and a pH value of 7. At this temperature and pH, they can convert food waste into biogas within a cycle of about 24 hours.1 kg (dry weight) of food waste yields about 1 kg (about 800 litres) of biogas. To get the same quantity of biogas from dung, one needs about 40 kg dung, and a fermentation period of about 20 days. The calorific value of biogas will be about 4000 kCal per kg. The waste material to be fed into a biogas plant should contain only biodegradable organic material. Other organic products like plastic, rubber, petroleum, hooves or wood cannot be digested by the methanogens. Introduction of any toxic or bactericidal material into the biogas plant would kill the methanogens and the system would stop producing methane. Increase in the population density of non-methanogenic organisms causes reduction in that of the methanogens, inhibiting the formation of methane.