The fourth option in the waste hierarchy is recovery. Recovery is about finding other uses for wastes that enable some value to be extracted or recovered from them, usually by using them as a source of energy.
Recovering energy from waste on a large scale using an advanced incineration plant is a high-technology, high-cost option that is common in many developed countries. However, it needs a highly developed infrastructure (a reliable source of waste, good roads, a reliable waste collection service, a power distribution grid, etc.) and large amounts of waste. This technology is currently rarely used in low- and middle-income countries, but as cities develop there is great potential for energy-from-waste in the future (Scarlat et al., 2015).
In Study Session 5 you learned about the production of biogas from excreta by anaerobic digestion using the biogas latrine. The same technology can be used to treat food waste on its own or in combination with human excreta or animal manure.
Biogas recovery from organic waste (Figure 8.6) can be done at the kebele or household scale, where the biogas can be used for cooking and heating water. The sludge from the digester can be used as a fertiliser and soil improver. Another benefit of biogas production is the reduced use of fuel wood, which improves living conditions by reducing indoor air pollution. Additionally, biogas contributes to the reduction of greenhouse gases. The use of biogas as a cooking fuel will mainly benefit women because it will reduce their overall workload by providing energy for the household without requiring labour-intensive fuel collection.
Biogas production needs more equipment than composting, so it is more expensive to install. It also requires greater expertise than composting to operate and the equipment must be maintained. Small-scale biogas is well established in China and India, but this method is still relatively uncommon in other low-income countries (Rajendran et al., 2012).