Digestion? Composting? Steaming? After years of it being seen literally as waste, in the past few years industry is finally waking up to the potential of our rubbish. “We’re looking at a kind of industrial revolution,” says Richard Kirkman, head of technology for Veolia Environmental Services. “We’re making factories to make raw materials from waste, to put those materials back in the economic cycle. That’s our business model.”
One of the most interesting prospects in waste disposal is anaerobic digestion (AD), which is suitable for easily biodegradable matter. Waste is sealed in oxygen-free and bacteria-rich conditions where it is digested. The end product is methane, which can be used in gas-fired power stations or fed into the gas supply, and a rich organic fertiliser for use in agriculture. AD is, essentially, hi-tech composting, needing only half the space and a third of the time to complete the process.
One government report suggests that by 2020, AD-derived biogas could, through electricity generation and domestic gas supply, account for 10-20TWh of the UK’s heat and power. At the upper end of the scale, that equates to 7.5 per cent of predicted demand.
A £32m New Technologies Demonstrator Programme, launched by the Department for Environment, Food and Rural Affairs (Defra), is also investing in a range of new ideas to help lessen the waste mountain. In-vessel composting, for example, is simply industrial-scale composting performed in a controlled environment, with the air flow and ambient temperature adjusted to sanitise waste and guarantee the quality of the final product.
Gasification and pyrolysis also have exciting potential. In the former, carbon-rich waste is heated in the presence of oxygen to break down hydrocarbons to form a biogas. Pyrolysis is achieved without oxygen to achieve a biogas with a different composition. In the days before North Sea gas, coals were subject to the same procedure in order to make fuel. The technology is not new, but the idea of using it for municipal waste is only just beginning to catch on.
Finally, mechanical heat treatment, used as a precursor to other forms of processing, is also being investigated. Piles of waste are steam-heated, sterilising the contents and reducing them to more manageable forms. Paper and card, for example, are reduced to a fluffy mass for further processing, and labels and lacquers are steamed off glass and metal, leaving them ready for reuse or recycling.
For Kirkman and Veolia, the next stage is to remove “the human interface” in material-recovery facilities. He says: “At the moment we have people picking stuff up off conveyor belts.
“In the same way that cars used to be made by people and now they’re made by robots, it’s within our capability to make a sorting centre without people touching anything.”
Control-centre-based touch screens allow a human operator to instruct a robot to move materials, or an infra-red “magic eye” identifies different types of plastic and uses a jet of compressed air to shoot an items into relevant bins.
But in the end, as Steve Lee, chair of the anaerobic digestion task group and chief executive of the Chartered Institution
of Wastes Management, points out: “We still talk about waste management as something inevitable. What about waste prevention?
“We’ve been living an uncontrolled party for the past 50 years and one day historians will look back on this era agog. We understand materials and our responsibility towards them much better now, so we need to start talking about how we can design out waste completely.”
Sarah Lewis-Hammond is an award-winning environmental journalist
Good Riddance to Rubbish
Poo into power
Faeces, animal or human, make great biogas. Just pop the poop in a methane digester and two weeks later out come fertiliser and methane. Thames Water says it saved £15m and powered 14 per cent of its operations this way in 2008.
Hydrogen from pee
Researchers at Ohio University have found that hydrogen atoms in urea are more loosely bonded than those in water, so electrolysis easier and cheaper.
People power
Systems are popping up, from the Japanese railway generating electricity from the vibrations of passengers going through ticket barriers, to
the London nightclub dance floor that turns kinetic energy into electricity.
Tornado power
The Canadian engineer Louis Michaud claims that warm air lost from power stations could be used to create intense vortices, inside which wind turbines would utilise the 200mph tornadoes.
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