biodegradable [municipal] waste (domestic FW) to reduce the global warming potential (GWP) of greenhouse gas emissions. Landfilling FW has a GWP of +743 kgCO2e/tFW. Taking FW out of the waste stream makes separation of dry recyclables easier. Home composting is ideal in many ways, though it is difficult to determine its GWP because there is a range of skill in managing the process. However, many are unable or not inclined to undertake home composting.
Kerbside collection involves storing FW, which has a number of disadvantages. FW is not ideal for centralised composting because of its high moisture content and biodegradability, the route has a GWP of -14 kgCO2e/tFW. In contrast, centralised AD has a GWP of -162 or -215 kgCO2e/tFW depending whether sanitisation is by pasteurisation or thermal hydrolysis (TH). Retrofitting TH to increase the capacity of existing AD is a good commercial opportunity for water companies, as well as environmentally virtuous. Local authorities and others are waking up to the idea that food waste disposers divert FW at source, are convenient, and welcomed by householders. Field studies have demonstrated they do not adversely affect sewerage or wastewater treatment infrastructure. Where the sludge is treated by AD and the biogas used for electricity, the GWP of this route is -199 kgCO2e/tFW.