International Journal of Renewable Energy and Environmental Engineering ISSN 2348-0157, Vol. 03, No. 04, October 2015 IJREE 030401 Copyright © 2015 BASHA RESEARCH CENTRE. All rights reserved Possibility of Anaerobic Co-digestion of Cafeteria, Vegetable and Fruit Wastes for Biogas Production without Inoculum Source MUHAMMAD RASHED AL MAMUN, SHUICHI TORII Department of Mechanical System Engineering, Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555 Japan Email: rashedshahi@gmail.com Abstract: Co-digestion of cafeteria, vegetable and fruit wastes was anaerobically digested, in order to recover methane as a source of renewable energy. Here we report the optimal biogas production and methane yields from variable mixing ratios without bacteria inoculums added using batch digesters under mesophilic conditions. The lab scale digestion experiment was carried out in 200 L polypropylene digesters. The result showed that the co-digestion process significantly influenced the biogas and methane yields. The maximum biogas yield obtained for the mixing ratio CW:VW:FW of (0.5:1.0:1.5, 1.0:1.5:0.5, 1.5:0.5:1.0 and 1.0:1.0:1.0) were 33.92, 35.52, 36.55 and 43.87 L/d, at the 25th, 24th, 24th, and 21th day, respectively. The cumulative result showed that an increase of 48.3%, 19.95%, and 8.61% gas yields of mixing ratio CW:VW:FW (1.0:1.0:1.0) compared with other ratios of CW:VW:FW (0.5:1.0:1.5, 1.0:1.5:0.5, and 1.5:0.5:1.0), respectively. It was observed that the average methane concentration CW: VW: FW of (0.5:1.0:1.5, 1.0:1.5:0.5, 1.5:0.5:1.0 and 1.0:1.0:1.0) were 59.95%, 60.07%, 61.41%, and 63.61%, respectively. Thus, the optimum mixing ratio suggested that the co-digestion technique can be promising to produce valuable gas products and to reduce environmental pollutions simultaneously. Keywords: Anaerobic co-digestion, Renewable energy, Methane, Cafeteria waste (CW), Vegetable waste (VW), Fruit waste (FW) Introduction: In today’s energy demanding life style, there is a need for exploring and exploiting new sources of energy that are renewable, as well as, eco-friendly. Due to rapid growth of population and uncontrolled and unmonitored urbanization has created serious problems of solid wastes Management and change in global climate [1]. Solid disposal treatments such as incineration and pyrolysis have an air pollution problem with high initial investment cost [2]. It is predicted that the conventional (oil, coal, natural gas etc.) energy may last for another six to seven decades which has lead to global climate change, environmental degradation and human health problems [3]. The renewable energy resource systems such as solar, wind, hydro wave, geothermal and biomass offer attractive prospects because they are unlimited and cheap [4, 5]. Biomass considered as a worldwide valuable energy alternative to fossil fuels, because it may be converted to a variety of usable forms of energy such as biogas, and liquid transportation biofuels through anaerobic digestion (AD) [6]. (AD) is a waste-to-energy technology biological process that produces biogas by bacteria under poor or no oxygen conditions [7-10]. It is a colorless, flammable gas produced from different high-strength biowaste, such as municipal primary and secondary sludge, organic portion of kitchen waste, pulp and paper sludge, agricultural offfarm and on- farm residues including animal manure into methane- rich biogas [11-17]. The digesters are incubated at mesophilic (25 – 35 ℃) or thermophilic (45 – 60 ℃) conditions for a certain period of time. It is a multi- step biological process where the organic carbon is mainly converted to carbon dioxide and methane [18]. The process can be divided into four steps: hydrolysis/liquefaction, acidogenesis, acetogenesis and methanogenesis. The mechanisms of anaerobic digestion process as shown in Fig. 1. Figure 1 Mechanisms of Anaerobic digestion Process [19]