Energy from Waste: Reuse of Compost Heat as a Source of Renewable Energy

An in-vessel tunnel composting facility in Scotland was used to investigate the potential for collection and reuse of compost heat as a source of renewable energy. The amount of energy offered by the compost was calculated and seasonal variations analysed. A heat exchanger was designed in order to collect and transfer the heat. This allowed heated water of C to be obtained. The temperature could be further increased to above C by passing it through multiple tunnels in series. Estimated costs for installing and running the system were calculated. In order to analyse these costs alternative solar thermal and ground source heat pump systems were also designed. The levels of supply and economic performance were then compared. A capital cost of 11,662 and operating cost of 1,039 per year were estimated, resulting in a cost of 0.50 per kWh for domestic water and 0.10 per kWh for spatial heat. Using the heat of the compost was found to provide the most reliable level of supply at a similar price to its rivals. 1. Introduction Composting is an aerobic process where organic materials are biologically decomposed, producing mainly compost, carbon dioxide, water, and heat. Conventional composting processes typically comprise four major microbiological stages in relation to temperature: mesophilic, thermophilic, cooling, and maturation, during which the structure of the microbial community also changes, and the final product is compost [1]. In recent years, the development and widespread use of more expensive in-vessel systems for the processing of biowastes has resulted from legislative pressures on the safety of the composting process and the subsequent use of the compost product [2]. Such systems allow for much more precise control of the composting process particularly in terms of moisture and temperature control [3]. Thus, current composting approaches and technologies tend to emphasize the use of high temperatures ( 7 ) in order to meet regulatory requirements for pathogen control [2]. Compost has been widely used as soil conditioners and soil fertilizers. This practice is recommended, as soil fertility needs more than ever to be sustained. Food demand is increasing rapidly in non-OECD (Organisation for Economic Co-operation and Development) countries, and it is in those countries particularly where organic waste needs to be diverted from landfill sites to composting practices, so compost can enhance soil fertility [4]. In OECD countries, where composting of organic waste is already established, its use as a landfill cover to abate greenhouse gas emissions has