Waste processing may not be the sort of thing you’re likely to hear being discussed around the dinner table, but as the old adage goes “where there’s muck there’s brass”. According to one pioneering scientist from the University of South Wales, it’s more a case of “where there’s muck, there’s energy, fertiliser and resource recovery”.

Professor Sandra Esteves is a leading authority on 'anaerobic digestion' - the method by which human, animal or food waste is broken down to produce biogas, biofertiliser or various other resources. The natural alchemy happens in large, sealed, oxygen-free tanks, by using special microbes to process the waste, separating out useful gases and nutrients.

It's this technology which is crucial to help combat climate change in Wales, according to Professor Esteves:

 “If you talk about marine, solar or wind for example, those are energy-related technologies only. But AD doesn’t just provide us with energy, it also provides the ability to reduce the impact of the waste that we generate. It stops us from emitting methane in the wrong places, while carbon dioxide can be recovered as well.

“Anaerobic digestion is a technology that ticks so many boxes for this reason. Yes, we can drive it to produce the energy that we need but we can also direct it at chemical, fertiliser or protein production."

"We can recover valuable nutrients such as phosphorous, an element which is becoming depleted very quickly globally.

Esteves explains that the resources recovery process is driven by microbes. 

"Generally microbes have a  low chemical input and require low temperatures and low pressures. Plus they don’t need to get paid, which is a bonus in today’s world.”


According to Wales Recycles we throw away more than 400,000 tonnes of food waste every year. Anaerobic digestion is the Welsh Government’s preferred option for processing it. But AD plants can also process sewage, animal slurry and garden cuttings.

Wales has around 40 AD plants and the applications of this renewable technology are wide-ranging due to its versatility.

“It’s a process that can be tweaked to suit the needs of different parts of Wales and that’s one of the most important aspects of it," says Esteves.

“The applications of AD in Pembrokeshire, where there’s a huge farming community, might not make the same sense as they would in the middle of Newport. So it’s about being adaptable according to the Welsh region.”

Estimates vary, but livestock are calculated to be responsible for up to 14 per cent of all global greenhouse emissions from human activities, according to the United Nations.

Esteves argues that one of the ways to minimise the impact of agriculture is anaerobic digestion.

“Agriculture is very heavy in terms of emissions, and cattle farming in particular. But farmers are very keen to engage and to do better things because they know they’ll likely be passing the land on to their children and they therefore have a responsibility to future generations. I think that sometimes they need guidance and help from government and others on what the possibilities are.

“In the past, we have all been a bit like sheep, following the same patterns and processes. But too much of a good thing is a poison. So we need to be adaptable as a society and especially when considering climate change.

"That means if we have an excess of energy in one place then we should be targeting the use of that resource into another application. There’s very little point in putting out more of what we already have. It’s a case of balance and strategic thinking.

“Yes, we do need to manage our systems better. But I think the future is bright, especially in Wales.”