2. Director of Institute of Energy Futures, Brunel University London, Uxbridge, Middlesex, UK.
The UK food chain was responsible for 18% of the total UK energy use and produced 32% of the country’s greenhouse gas (GHG) emissions in 2011. The holistic food chain is estimated to produce around 15Mt of post-farm gate food waste, corresponding to 15% of overall food purchases. The UK Waste and Resources Action Programme (WRAP) estimates that post-farm gate food waste is responsible for more than 20MtCO2e emissions, making 12% of total direct food chain emissions. The majority of post-farm gate food waste comes from households (7.2Mt) and the manufacturing sector (3.2Mt). This waste is largely disposed to landfill. The agricultural sector was found to account for approximately 90Mt of organic material waste, mostly in the form of manures and slurries. In addition to contributing to GHG emissions, wastes also depict a financial and resource flow weakness in the economy. As a result, the UK government is actively promoting energy recovery from waste, particularly through Anaerobic Digestion (AD) systems. This paper explores the energy generation potential of food-chain wastes (i.e., food and manure/slurry wastes) employed in AD systems to produce biogas, which is in turn used in combinations of Combined Heat and Power (CHP) and Organic Rankine Cycle (ORC) systems to generate power. Future scenarios on the amount of wastes are developed, and the relative potential of the technologies are investigated. The addition of ORC system with conventional CHP systems have shown to increase the electricity generation potential, at the expense of heat generation. The impacts of the implementation of these technologies are determined from observable trends in the literature, and are intended to be illustrative rather than predictive. For the case of this paper, the ‘Gas Turbine CHP with High-Grade ORC’ has shown the highest energy generation potential upto 2050 for the UK economy.
Keywords: Food chain wastes, anaerobic digestion systems, renewable energy technology, biogas