For British company QUBE Renewables, dealing with the kinds of materials nobody else wants to handle is all in a day’s work. “We’ve digested a lot of wild and wacky stuff” says Mark Clayton, QUBE’s Technical Director. He reels of a list that includes human waste, cow’s udders, granulated sugar, seaweed, biodegradable cutlery, and what he will only refer to as things that “we’re sworn to secrecy about by our clients.”
QUBE are in the business of creating small-scale modular anaerobic digestors to produce fuel for cooking, electricity, and even transportation. They’ve developed a line of products with names like BioQUBE, LagoonQUBE, QuickQUBE and DryQUBE, all of which allow their customers to produce biogas from unwanted waste materials.
Anaerobic digestion is of course nothing new. The European Biogas Association, in its annual review last year, identified over 17,000 biogas production plants across the EU. The energy produced by these facilities accounted for 60.6 terawatt hours of gas-fired power generation annually – equivalent to about 15 Hoover Dams.
In Asia, anaerobic digestion has also been around for a while, but is typically carried out on a much smaller scale. China has over 40 million household digesters installed in rural communities, processing manure, sewage and household waste to produce gas mostly for cooking and heating. India and Thailand also have government schemes to promote the uptake of anaerobic digestion. But these types of household digesters are rudimentary and inefficient, and most of the population still relies on more polluting fuels such as solid biomass, coal or LPG.
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Plug-and-play
QUBE’s idea was to combine the advantages of both worlds. “Our whole approach is that we design [the digesters] properly, build them in a factory then ship them, ready to go, plug-and-play,” says Clayton. That allows QUBE’s units to deliver efficient feedstock conversion while also remaining suitable for small-scale applications in off-grid locations.
The company also wanted to create a solution that was highly adaptable. “The approach was modular, but customisable if you like,” says Clayton. “You could choose how many units you wanted based on how much waste you had, you could choose whether you wanted to generate electricity, or whether you wanted to do heating, or whether you wanted to upgrade the gas to biomethane for use in vehicles, for example.”
QUBE’s emphasis on adaptability can be traced back to the company’s origins. A spin-off from environmental consultants Aardvark, the idea came about after the consultancy was approached by the UK Ministry of Defence. The MoD needed a way both to deliver energy to forward operating bases in conflict zones, and deal with the solid and liquid waste disposal problem created by having a large number of soldiers bivouacked in a very small area.
The solution had to be something that could be deployed easily and at a minimum of expense. It’s a way of approaching biogas production that QUBE have remained true to. For instance, the bioQUBE is built inside of a shipping container to take the hassle out of transportation. “We developed those just because shipping containers are a standard piece of kit to pick up and move around,” Clayton explains. “Lorries pick them up very easily, boats take them very easily, and with a bit of ingenuity you can move shipping containers on the back of pick-up trucks for example… They’re also safe, strong and secure.”
Then there’s the quickQUBE, the company’s smallest-scale small-scale digestion system. Delivered in flatpack form and aimed primarily at military users and humanitarian missions, a single quickQUBE unit can be set up with a digestion capacity of as little as 5m3. At this size it is able to digest around 51 tonnes of human sewage per year, and produce 5187m3 of biogas – enough to cook for 11,350 hours on a 1.5kW stove. By comparison, one 40ft bioQUBE unit is able to produce 79,380m3 of biogas annually.
The quickQUBE in action
The economics of small-scale biogas
For remote locations and military bases modular anaerobic digesters may well be the only option available. For everyone else, the advantages come down to emissions reductions, reliability, and perhaps most persuasively, financial savings.
“There’s two different models there” for garnering savings, Clayton says. “One is the cost of the energy displaced.” In many locations without access to reliable electricity from the grid, the costs of obtaining electricity from diesel generators or other means can be steep – “up to 60 pence per kilowatt potentially, if fuel is very expensive,” Clayton says. In those types of contexts, particularly in rural communities with plentiful supplies of biodegradable waste, small-scale biogas is an obvious choice.
The other model is through reducing the costs of waste disposal. Clayton likens the QUBE to “a mechanical cow… you shove stuff in the front end, as you would do with a cow, and you get exactly the same sort of volume of material coming out of the back end.” This material – called the digestate – has been converted by the digestion process into something that is essentially benign, regardless of how noxious the original feedstock may have been. It also has great value as a fertiliser, which comes in handy in agricultural settings. “It’s a transformative business basically,” Clayton says.
Given the savings from both displaced energy costs and reductions in the cost of waste disposal, QUBE’s assessment is that the typical payback period after investing in a digester is less than six years. That contrasts with an estimated functional lifespan for QUBE anaerobic digesters of ten years or longer.
Merging with the microgrid
Many of the markets QUBE Renewables are targeting – whether that’s the military, refugee camps, or rural communities in the developing world – are also prime testing grounds for off-grid solar and microgrid projects. Fortunately, Clayton points out that small-scale anaerobic digesters and microgrid solutions make excellent bedfellows.
“We see anaerobic digestion as providing very good, stable baseload power for those networks,” he says. The advantages of biogas are that it is able to be produced year round, and that it “can be stored relatively easily… either in gas form, or upgraded and pressurised in bottles. Biogas has really good co-generation properties in those microgrid environments.” Alternatively, the fuel can be directed to handle more energy intensive activities like cooking and heating, while renewables can be used for lighting, charging phones and powering appliances.
Given that there are still around a billion people in the world without access to power, the potential market for small-scale biogas is pretty extensive. For QUBE and companies like them to tap into that market, however, there are still a few hurdles to clear. Clayton identifies a growth in public resistance to fossil fuels, and rising prices for energy from emissions intensive sources as potential gamechangers.
But in the near term, it’s serviceability that is the real challenge. “As I alluded to before, you’ve got a mechanical cow here. So you need a good herdsman so to speak, and you occasionally need to call the vet,” Clayton says. What is needed is “more people out there understanding the benefits of biogas, becoming trained and adopting the technology.”
Header image shows the dryQUBE being trialed in the Philippines to produce biogas from rice straw.
