Anaerobic-digestion plants: interview with Mike Mason, World Petroleum Council Guide: Biofuels, 2016

Anaerobic-digestion plants: interview with Mike Mason, World Petroleum Council Guide: Biofuels, 2016


Tropical Power chairman Mike Mason tells us of his plans to power Africa by copying a cow’s stomach

[Mike Mason is a lecturer at Oxford University as well as a chairman if a green-power company. When I interviewed him he was a world leader in alternative energy, and by the look of it, still is. In the future, we’ll all have anaerobicdigestion plants in our back yards. I found all this stuff fascinating.]

World Petroleum Council Guide: Biofuels, 2016

We may regard animals like lions and eagles in royal reverence but when it comes to majestic power, the cow has been overlooked. Don’t be fooled by the dewy-eyed gazes across five-bar gates, for it is the cow – or rather, its digestive tract – that holds the secret to abundant, inexpensive energy.

A cow’s stomach is a highly efficient anaerobicdigestion (AD) unit, a fact understood by Mike Mason who leads research programmes at Oxford University on AD technology, as well as energy crops for semi-arid regions and hybrid AD/solar systems. In 2013, Mason founded Tropical Power and associate companies Biojoule and Solarjoule in order to construct AD and solar plants in Ghana and Kenya. The Tropical Power-built 2.8MW Gorge Farm site at Naivasha in Kenya is the largest AD power plant in Africa – and more are planned.

WPC: Gorge Farm is the largest plant of its kind in Africa. How is that working out?
Mike Mason: It took us a long time to secure the power-purchase agreement, and because it was the first of its kind on that scale, we had all sorts of issues with things like bringing in the right skills and building large concrete structures. But effectively, it’s all done and it all works.

Do you have plans to build more in Africa?
We have an ambition to do more. We’re still sorting out a few issues with the first plant. There are always teething problems, biology problems, and so on. We’re building up our feedstocks and waiting for new features to come on board. When we’ve got it up to full power, we’ll set up the next.

What feedstocks are you using?
Agricultural waste. At present, there isn’t as much as we’d like, so we’re building the feedstocks up.

We understand that your long-term aim is to make an AD plant work as efficiently as a cow’s digestive system.
AD plants use bacteria that are similar to, or the same as, those from cows. But a cow does the rate-limiting step, breaking down cellulose, up to 30 times faster than an anaerobic-digestion plant. What we’ve built is conventional technology. My research is to emulate the high speed of the cow.

Why can’t we do that now?
I don’t know yet. We’ve got strong clues as to how it might be working and we’ve got laboratory tests going on, a proof of concept trial to see if we’ve got the right idea. There’s probably a few years of work in it but we’ll see if we can make it happen.

What will that mean once you get to that point?
It will dramatically reduce the cost of anaerobic digestion as a source of renewable energy.

Where do you see Tropical Power in 20 years?
My research has two components. One is getting the cost of anaerobic digestion down. The second is developing new, hyper-water-efficient crops that we can grow on semi-arid land, where we’re not competing with food and not competing with wildlife. We are focused on working with a photosynthetic mechanism called crassulacean acid metabolism. This can be up to ten times as water efficient as mechanisms used by ordinary crops. Put those two things together and you have a proposition that is cost-competitive with coal.

Do you think there’s enough time and effort being put into renewables?
No. I think what we lack is a sense of urgency and focus about dealing with the solutions. We need to put these things on a wartime footing and say, “We have to solve these problems.” The more we spend on research the less we have to spend on subsidising things that are uneconomic. LG


What is anaerobic digestion?
AD biogas – roughly 60% methane, 40% carbon dioxide – is created through the digestion and decomposition of organic matter by micro-organisms in the absence of oxygen. Feedstocks can include crop waste, food waste and manure. The biogas that is made, when combusted in a gas engine, can be used to generate electricity and heat; alternatively, pure methane can be injected into the mains gas grid or used for transport. The remaining nutrient-rich digestate can be used as a fertiliser.