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Waste not, want not

We produce of lot of waste. Some is a potential source of energy. That may even include the carbon dioxide produced from combustion.

We usually treat carbon dioxide as a problem. But it can also be a solution. There are some interesting new ideas about using it to make fuels. One option is to use it to enhance algae growth. This can of course be done, in principle, with any bio-crop in large glass houses or other gas-tight enclosure: gas-engine exhaust is already used in commercial glasshouse horticulture for tomatoes etc, e.g. in Holland. But algae absorb CO2 more rapidly. MIT’s carbon-capture and algae-bioreactor system is interesting. ( However there are evidently issues of maintaining efficient reactions, and the US company involved with this, GreenFuel Technologies, evidently has had financial problems. But trials by Sheffield University, using captured CO2 (from Tata steelworks near Scunthorpe) bubbled through algae tanks, are showing some promise:

Meanwhile Swedish utility Vattenfall has launched a pilot project using algae to absorb greenhouse-gas emissions from a coal-fired power plant in eastern Germany in a €2m trial run. Half the funding for the MiSSiON (Microalgae Supported CO2 Sequestration in Organic Chemicals and New Energy) project comes from Vattenfall, the other half from state and EU subsidies. The flue gas emitted at the Senftenberg brown-coal fired plant is being pumped through a broth using algae cultivated in 12 plastic tanks. The biomass produced can be used to produce biodiesel, to feed biogas power plants and as a nutritious supplement in fish food.

In a somewhat similar approach, Carbon Sciences Inc. says it’s developing a technology to transform greenhouse gases into liquid portable fuels, such as gasoline, diesel and jet fuel. ‘We are developing highly scalable clean-tech processes to produce liquid fuels from naturally occurring or human-made greenhouse gas emissions. From sources such as natural gas fields, refinery flare gas, landfill gas, municipal waste, algae and other biomass, there is an abundant supply of inexpensive feedstock available to produce large and sustainable quantities of liquid fuel to replace petroleum for global consumption, thereby eliminating our dependence on petroleum’.

Much more radical is the idea of reacting CO2 with hydrogen produced by electrolysis using electricity from wind turbines, to make methane and synfuels. See the UK ‘Air Fuels’ project and the various German/EU projects e.g CO2RRECT
I’ll be looking at this ‘wind-to-green-gas’ idea more in my next blog.


We also treat municipal and domestic solid waste as a problem, sometimes just letting it rot in landfill sites producing methane – a powerful greenhouse gas. Some of that gas can be and is captured, providing a cheap renewable fuel, but if it’s burnt to generate power then you get carbon dioxide, although that could be captured and stored. Then the energy would be carbon neutral or even carbon negative, given that the production of food/farm waste has involved the absorption of carbon dioxide.

However, there are also other approaches, such as controlled anaerobic digestion of food/farm waste algae, with the emphasis on high-value food products rather than energy production. For example, start-up company Merlin Biodevelopments based in North Wales has devised a new way of growing protein-rich algae from waste food and cow slurry, which can be used in high-protein food products for human and animal consumption. An array of reactor tubes, in which the algae are cultivated, has been built in a polytunnel at the Moelyci Environmental Centre, Tregarth, near Bangor. So far Merlin has invested £500,000 in the project, including R&D grants worth £160,000 from the Welsh Assembly Government. It’s designed its own low-cost micro AD plant, and its single 30m long polytunnel can produce 20 tonnes of algae a year. A second plant is due to open in south Wales soon and Merlin expects to be producing 1,000-2,000 tonnes by 2013. They say a 210 sq m polytunnel can produce as much protein in a year as 10 sq km of top-grade agricultural land. In a side project at Moelyci, Merlin is also investigating the value of processing AD residue into high value fertiliser using the algae system.

Using food waste for AD is clearly sensible. As I’ve noted before, Gwynedd Council are backing a new AD plant, which will process around 11,000 tonnes of food waste each year; converting it into renewable electricity and biofertiliser for use on nearby farmland. The food waste will be collected from local homes and businesses via a collection scheme run by Gwynedd Council. The new plant will replace the existing landfill site. It will be the second waste-fed anaerobic digestion plant built in Wales, following the construction of the Premier Foods plant last year near Newport.

In addition, food waste from homes in South Gloucestershire is now also being converted into renewable energy and organic fertiliser at a single site via AD. Food collected at the kerbside is being sent to an anaerobic digestion plant in Oxfordshire to be broken down by bacteria into useful gases and organic materials. The long-term arrangement with operator Agrivert, brokered by the council’s waste collection contractor Sita UK, will see about 6,000 tonnes of food waste processed each year – equivalent to the weight of rubbish carried in 600 full refuse lorries. Agrivert manager Harry Waters said the company would expect to capture two million kilowatt hours of renewable energy from that amount of food waste every year. He said: “That is enough to power more than 400 family homes and produce organic fertiliser which will be used by farmers to grow food on more than 700 acres of land. Moreover, we capture a million cubic metres of methane that would otherwise be released to the atmosphere.”

One way or another the AD biogas option looks likely to become increasingly important. The Anaerobic Digestion and Biogas Association recently said the Chancellor’s efforts to give shale gas a helping hand with a ‘generous tax regime’, would be better spent on other forms of gas which are renewable, like biogas. The ADBA suggests biogas from anaerobic digestion (AD), ‘which can provide energy security at a lower cost and, since it’s renewable, with far lower carbon emissions and environmental impact than more experimental technologies like shale gas. AD can be scaled up fast and cheaply and with the right support could generate 40 TWh of biogas, equivalent to 10% of
the UK’s domestic gas demand, at the same time as boosting economic
growth and creating 35,000 jobs.’

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