Solutions for unavoidable food waste
Unavoidable food waste is a resource. By its very nature, it contains nutrients and energy, and therefore solutions should seek to maximise the resource potential in the materials.
AD is a proven technology solution widely used in the water treatment industry, and was cited by Defra in its 2011 Waste Review as the preferred option for food waste. There are now 110 AD plants in the UK and a further 200 have received planning permission.
In simple terms, AD is a biological process that operates in much the same way as a human stomach. It produces a solid, liquid and gas and there are a number of possible uses for the methane gas it produces. AD could be used to process 5m tonnes of unavoidable food waste, generate 1.1TWh per annum of renewable electricity through traditional combined heat and power (CHP) systems and provide employment to over 4,000 people.
AD also creates a low-carbon bio-fertiliser and could return up to 4m tonnes of digestate, and over 1.4m tonnes of nutrients to the soil each year.
In-Vessel Composting (IVC)
IVC is an extension of open windrow composting, where organic material is laid out in exposed rows and repeatedly turned so that it degrades naturally under an aerobic process. In 2010, approximately 5.4m tonnes of material, largely green waste, were composted in the UK and produced coarse 0-40mm grade compost for use in agriculture with an estimated value of £9.2m. However, whilst this ensures that nutrient content and organic matter can be returned to the soil, unlike AD, it is not a source of biogas.
Rendering plants are also capable of handling unavoidable and high-risk, Category 1 and 2 ABPs. The process is the same as the low risk material, but the potential markets are more limited. The resultant tallow can be used in the production of biodiesel and meat and bone meal (MBM) can be used as a biofuel to generate renewable energy.
Energy from Waste (EfW)
In 2012, 24 EfW plants in England treated almost 4m tonnes of residual municipal solid waste (MSW) and solid recovered fuel (SRF).42 Waste-derived renewable electricity from thermal combustion is forecast to grow from the current 1.2TWh to between 3.1TWh and 3.6TWh by 2020.43
Macerators/Waste Disposal (FWD) Units
Macerators have been used in various sectors for many years, particularly the hospitality sector, as a low-cost means of disposal. FWD units are more commonly associated with small-scale use within the domestic environment. A report commissioned by the National Food Waste Programme concluded that, “Kerbside collection of segregated domestic kitchen food waste was shown to have lower GHG emissions and overall financial costs when compared with the use of domestic FWD units.’’44 Furthermore, once the cost of blockages was factored in, the expenditure on FWD units further increased, which suggests that macerators and FWD units may not deliver the best economic or environmental outcome for food waste.
42 Defra February 2013: Energy from Waste: A Guide to the debate
43 Defra February 2013: Energy from Waste: A Guide to the debate
44 Water Research Centre – National Food Waste Programme (Work Package1.1) Comparison of the Sustainability of Food Waste Disposal Options 2010