By Hugo House, Good Energy

At Good Energy, we've begun our project to assess and improve sustainability at River Cottage. We'll be doing a detailed evaluation of their consumption of energy and resources, but we've already identified one key area for improvement, and that's the way they cook. RC use LPG - Liquefied Petroleum Gas - to fuel their cookers. LPG is an excellent cooking fuel, but it is a fossil fuel and burning it is contributing to climate change.

So, is there a fuel that's as manageable and responsive as gas that doesn't harm our environment? Of course, 100% renewable electricity is a zero-carbon fuel that can provide the necessary heat, but even the best induction hobs don't offer the flexibility that professional chefs require. It has to be gas, so is it possible to source ‘green' gas?

The natural gas that we extract from the North Sea is methane, CH₄. Burning it in air creates two new compounds: water vapour (H₂O) and carbon dioxide (CO₂). It began to form millions of years ago when organic life in our seas died and began decomposing on the seabed with the help of bacteria. When organic matter (like small sea creatures) decomposes without any oxygen present (like on the sea bed) the process that occurs is called Anaerobic Digestion. Its byproducts are carbon dioxide and methane, which were stored beneath the seabed until mankind started extracting them in the twentieth century.

Nature's process of Anaerobic Digestion (AD) can be replicated artificially. More than 4000 AD systems operate in Germany and interest is growing fast in the UK. Using ‘feedstocks' of food waste, animal slurry or energy crops (like maize), or a combination of these, bacteria inside the AD digesters go to work, breaking down the feedstock to create biogas. This biogas is burned and the energy used to drive a turbine to generate electricity. The residual heat is often put to use drying grain or heating greenhouses for example.

When biogas is burned to create energy, it returns the same amount of CO₂ to the atmosphere as if the feedstock had decomposed naturally. This means that properly managed biogeneration doesn't disturb the carbon balance and doesn't contribute to climate change. The AD process creates another byproduct - the digestate - a highly nutritious, pasteurised, organic fertilizer that can be applied to farmland. So far so good ... as AD can use waste food, it can help to divert some of the 20 million tonnes of food waste produced annually in the UK from landfill.

So AD has the potential to be a win/win solution! The next step is surely to identify an AD system, get some biogas from them, and see if the chefs at River Cottage can cook on it...

Luckily, of the small number of AD plants in the UK, a few are quite near River Cottage. We spoke to the farmer, told him our plan which raised a smile and then we started to talk logistics. Unfortunately we got snagged on a problem.

The biogas created by AD is a mix of about 60% methane, 40% CO₂ and some traces of other gases like hydrogen sulphide. This burns just fine at the generation end of an AD system but if you want a flammable gas suitable for cooking on, it won't work. You need to ‘scrub' biogas so that you are left with pure biomethane. As you might have guessed, scrubbing gasses isn't a question of getting on your hands and knees with a bucket of water; it involves a bit more chemistry.

So unfortunately this promising path we were exploring has reached a dead end. We need to find a supply of biogas that's been cleaned up and turned into biomethane. Next we need to find a safe method of getting it pressurized or liquefied and into a transportable canister. Anyway as one door closes, another is opening. I may have found our purist... or scrubber! Watch this space....