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Refuse put to use: the case for biomethane in the UK

Food waste and other organic materials are processed in an anaerobic digestion plant — like the one pictured above — to make biomethane.

For many Britons, turning the heating on (or up) is a reflexive action for a large part of the year. So much so that approximately 47 percent of energy in the UK is used for heating –  which is in turn responsible for one-third of the country’s carbon emissions.  Suffice it to say that decarbonising heat is on the agenda for anyone seeking to reduce the UK’s carbon footprint, and one particular solution is increasingly sparking corporate interest: biomethane gas.

What is biomethane and how is it produced?

According to Dr. Kiara Zennaro, the Head of Biogas at the Renewable Energy Association, the UK has the fastest-growing biomethane sector in the world. Biogas is produced through anaerobic digestion –  a natural process in which plant and animal-derived material is broken down by microorganisms in an airtight container. It’s not wholly dissimilar to what occurs in your average garden compost heap, but an anaerobic digester must be a sealed vessel in which bacteria can work without the presence of oxygen.

“The microorganisms are pretty much the same,” Zennaro says of the difference between composting and anaerobic digestion. “They are already in the waste; you don’t have to add anything. In the absence of oxygen, they will break down material, though it will need some stirring and mechanical mixing to make it more effective.”

The type of organic matter ‘fed’ to a digester tends to fall into two categories: municipal food waste and other waste and residues (e.g. from agriculture or processing), and so-called ‘energy crops’ grown solely to be used in the process of making biogas. 

There are two major by-products of anaerobic digestion, the so-called ‘digestate’ matter and biogas. The former can be used as a crop fertiliser because of its nutrient-rich composition, while the latter, a methane-rich gas, can be burned at the site of the anaerobic digestion plant to generate both renewable power and heat.    

However, biogas still contains a relatively large amount of CO2 and other impurities. It must be further processed in order to be injected into the National Grid, where it can then be used for heat, electricity or transport in much the same way as traditional natural gas. This purified form of biogas is referred to as biomethane.  

Which businesses and organisations in the UK are currently using biomethane?

In March of this year, the state-of-the-art Leyland Filling Station, a collaboration between CNG Fuels and the National Grid, launched in Lancashire, with the facility set to open for business at the end of this year. It is the UK’s first high-pressure connected compressed natural gas (CNG) filling station and it exclusively supplies biomethane created from food waste. CNG can be used in place of traditional petrol, diesel or propane, and the station is capable of refuelling up to 500 HGVs in a single day.

“By being connected to the high pressure system, it means the carbon footprint is much lower when compared to other filling stations because it requires less energy demand,” Zennaro says.

With their large cumulative quantities of food waste, and long-distance transport needs, major supermarket chains have naturally started to notice the potential of biomethane. Waitrose is already powering two of the Scania tractors used at its regional distribution centre at Leyland using compressed biomethane from the nearby filling station.

Not to be outdone, Sainsbury’s has recently partnered with recycling and waste management company ReFood to power a handful of its stores with biomethane. Under the partnership, ReFood will collect food waste from two of the supermarket’s depots, convert it into gas and fertiliser at one of its anaerobic digestion facilities and inject the biomethane into the grid. A third party will then export the gas to select Sainsbury’s locations where it will be used to generate carbon-neutral heat and electricity. 

“I think we’re seeing an increased interest from energy consumers, from corporate companies like Diageo and big supermarkets,” says Zennaro of biomethane’s growing appeal.  “So far they have been mainly interested in green electricity, but now the green gas element is starting to raise more interest.”

What are the challenges currently facing the sector?

Zennaro sees biomethane as one of a growing number of renewable solutions that will need to be utilised in order to further decarbonise the UK’s energy sector. However, there are a number of legislative obstacles to its growth. 

“The main issue is that the policy landscape keeps changing,” she says.  “It’s very difficult for investors and developers to know what level of support we’ll have by the time they build a plant and the plant becomes operational.”

Biomethane plants are reliant upon the UK government’s Renewable Heat Incentive -- a policy introduced in 2011 in which the government pays a tariff on each kilowatt hour of biomethane injected into the grid. In recent years, the tariff has been cut through a budget control mechanism designed to apply reductions if a particular technology is developing too quickly.

In addition, suitable feedstock for an anaerobic digester can be surprisingly difficult to come by. The government intends to restrict the growth of energy crops and their use in biogas plants because of concerns that they will displace land that could be used for growing food crops. It follows that the industry could turn to food waste for feedstocks, but even that is easier said than done:

“Forty-five percent of local authorities in England are not collecting food waste, because food waste collections are quite costly and are not mandated by Government,” Zennaro says.

So, could biomethane ever become a market rival for traditional gas?

Policy restrictions aside, it is unlikely that biomethane will ever usurp natural gas singlehandedly. But this isn’t to say that it won’t account for an integral portion of the UK’s energy mix.  Biomethane will not be a rival but a partner to natural gas.

“We could probably meet 20 percent of the UK gas demand 2035,” Zennaro says. “There is a huge opportunity for biomethane to fuel heavy vehicles, buses, and decarbonise the transport sector, as well. We really lag behind in terms of achieving our target for renewable transport, and the Government really sees biomethane as strategic not just to decarbonise the transport sector, but to improve air quality, which is the other important issue.”

“There is huge potential, that’s the bottom line.”

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