New research has investigated a two-step anaerobic digestion approach that 'pressure-cooks' food waste to make biofuel. Using hydrothermal liquefaction, the process extracts the energy value from food waste and saves carbon at the same time.
By using this process before the anaerobic digestion takes place, scientists have found that nearly the entire potential energy value of the waste food can be recovered. The process essentially involves pressure-cooking food waste to make a crude form of bio-oil that is then further refined into a burnable biofuel.
Any remaining waste is left in a water-based state and is digested in just a few days by microbes. This then produces methane, which can generate electricity and heat on a commercial scale.
The new approach provides measurably better results than simply using anaerobic digestion on its own, which takes several weeks. It takes just a few minutes to process the waste in the hydrothermal liquefier and only a few days in the next-phase anaerobic digester.
The news is particularly good, as food waste is one of the biggest categories of rubbish that will otherwise end up in landfill. Across the world, around a third of food ends up as waste, according to the United Nations. Across industrialised nations, this represents almost $680 billion of waste every year.
Existing digestion and composting systems for wood waste are slow and inefficient. By adding the 'pressure-cooker' approach to the start, the energy recovery can be much faster. Details of the study have been published in the Bioresource Technology journal. If the research is now picked up and funded for commercial development, it could provide a relatively easy and low-cost way to treat one of the biggest forms of waste, produce clean energy and reduce carbon emissions.