“…Several countries in Asia and Africa, including China, India, Nepal, Bangladesh, Cambodia, Vietnam, Kenya, Rwanda and Tanzania, are launching massive campaigns to promote biogas technology [62]. Figure 2 shows three major types of domestic bio digesters commonly used in the developing countries [44,45,52,57,63,[69][70][71][72][73][74], i.e., the plug flow digester, sausage-bag or tubular/plastic digester, the fixed-dome digester or Chinese digester and the floating drum digester, also called telescopic digester or Hindu digester. Even if the gas collection method and design are different, the digestion process is the same.…”