Recession seems imminent. Climate change, energy and food shortages pose great threats. You may well wonder what links these thoughts: why might food and electricity compete, and what is this to Resource? The answer is soil health.

At the sixth International ORBIT Conference recently, Dr Enzo Favoino showed a map of soil organic matter to stress desertification south and west of the Alps. Land with less than one per cent organic carbon is virtually infertile (there are patches in semi-arid East Anglia), while areas that still have plenty of soil organic matter are often mountainous, forest or so remote as to be unsuitable for major food production. The fact is, our land needs to be nurtured.

But what can we do? Well, assuming we British are willing to invest a little bit of effort, commercial and consumer biowastes may be regarded as potential sources of renewable energy and soil organic matter with much-needed nutrients.

After all, there’s a lot available. Although the food industry tries hard to minimise waste via packaging, cooling and use as animal fodder, some three million tonnes of commercial food wastes arise in the UK every year. And even though TV chefs, WRAP et al try to eliminate the UK’s household food wastes, it is no more likely than King Canute’s advisers stopping the incoming tide! Some six million tonnes per year seems inevitable, as is the seven million tonnes per year of post-consumer biosolids.

And then there is the ‘green waste’. The misconceived government targets and subsidies for big, brown bins, combined with the promotion of decking and patios over vegetable beds by gardening programmes, seem to have reduced home composting. So now about three million tonnes per year of botanical wastes also need treatment.

In fact, UK waste management, water and sewerage sectors together treat some 16 million tonnes per year of biowastes.

The choice between anaerobic digestion (AD), which generates electricity and digestate, and aerobic composting (AC), which yields heat and compost, however, is not simple.

AD with combined heat and power (CHP) releases more energy as heat than as electricity and yields a fibrous digestate plus plant nutrients. But can that heat be used to replace fossil fuels? A leading European expert at ORBIT knew of no plant doing so. And you have to question whether it is environmentally beneficial to transport the liquid digestate, which contains most of the nitrogen, phosphorous and potassium.

AC, on the other hand – contrary to certain misleading assertions on which our government’s promotion of AD seems to have been based – produces more heat per tonne of food wastes than the total of electrical plus heat energy from AD with CHP. What’s more, AC’s principle product is soil organic matter that is as rich in plant nutrients as AD digestate. Again, although, as yet, no existing in-vessel composting facilities harness this heat to replace fossil fuels, if the UK playing field remains tilted by Renewables Obligation Certificates (ROCs) towards AD with CHP, combined heat and aerobic composting (CHAC) may never be tried.

So, does the renewable electricity from AD with CHP justify using this technology above AC? The answer cannot be a simple ‘yes’ or ‘no’ to please politicians, interviewers and investors. It depends on several factors: whether heat from these technologies can be used; when the waste-to-product transformation may stop so as to return as much organic carbon to soil as possible without pollution; whether biowaste collection and compost/digestate ‘miles’ can be minimised; and so on. Answers depend more on energy and carbon balances and the regulations that beset them than on monetary costs. International energy and food markets set prices, but subsidies like ROCs tilt playing fields – sometimes perversely.