Where there’s muck there’s brass: a sustainable approach to waste management

Andrew Czyzewski, The Engineer – Sustainability Supplement
May 2011

Technology that generates energy from waste could help the UK shed its ’dustbin of Europe’ tag.

There’s a scene at the end of the film Back to the Future where the now-modified Delorean returns from 2015 and Doc Brown hurriedly rakes through a garbage can to refuel the flux capacitor with household waste (having previously required plutonium to function to a tune of 1.21GW).

Setting aside recent debate on the merits of nuclear energy, the scene taps into an innate desire to make good use of our waste. The media play on this too, relaying a constant stream of eye-catching initiatives ’Crematorium could help heat council swimming pool’ and ’Pee power could fuel hydrogen cars’, to name but a couple. It is certainly comforting to know that our engineers are constantly devising new and clever ways to clean up after us, but to what extent have advanced waste technologies really pervaded our society at large?

While things are slowly changing, the UK has traditionally been the ’dustbin of Europe’ at its peak having the dubious honour of topping household waste league tables for 2004-05 by sending 23 million tonnes of the stuff to landfill. Left to sit, this belches out huge quantities of methane, which is around 23 times more potent than carbon dioxide in terms of its global-warming effect. Indeed, landfill gas accounts for three per cent of all UK greenhouse gases combined.

Historically, the attraction of landfill has been its low cost, the abundance of non-porous sub strata and the need to fill holes left by mineral extraction. It has been patently obvious for decades that this is simply not environmentally sustainable, but, as with many things, the most powerful recent driver of change has been a financial one.

The EU Landfill Tax is rising at a rate of £8 per tonne annually, now standing at £56 per tonne, while the EU Landfill Directive has set stringent targets for the reduction of waste sent to landfill, which must drop to 50 per cent of its current level by 2013 and 65 per cent by 2020. One key goal for waste management is not only to divert waste from landfill, but to generate useable energy from it through export to the electricity or gas grids. Waste initiatives don’t attract the same fanfare surrounding big wind or solar power schemes.

Nevertheless, a report by Cranfield University last year suggested that energy from waste (EfW) could account for half of all renewable power by 2020 (thus 7.5 per cent of the 15 per cent renewable contribution to total energy called for by the EU). The array of technologies that come under the bracket of EfW is something of a minefield, however, ranging from incineration with energy recovery to plasma gasification with syngas production. They all differ in their original feedstock, process and output and, of course, they are claimed to offer advantages over each other.

Renewable claims, in particular, have come under scrutiny of late. Dr Geraint Evans of the National Centre for Biorenewable Energy, Fuels and Materials (NNFCC) advises the government on the Renewable Obligation Certificate (ROC) scheme to which companies must adhere. ’If you make your diesel or electricity from car tyres that are more or less 95 per cent fossil based, then it’s not renewable even though people might tell you it’s renewable, they’ve got their facts wrong,’ he said. ’The paper of the baked-beans can is renewable, whereas the plastic that wrapped your steak is not. It’s still a good use of resources, but there’s an important distinction.’

One largely renewable technology currently being pushed by the government is anaerobic digestion (AD). Here, organic and food waste is fed into sealed bioreactors where special micro-organisms digest it to produce methane, which is burned to generate electricity or ’cleaned up’ and exported to the gas grid. There are currently around 37 AD facilities in operation, mostly dealing with farm waste, with an additional 60 in various stages of planning.

In its latest recommendations, the Department of Energy and Climate Change (DECC) suggests AD installations up to 250kW be eligible for feed-in tariffs of 14p/kWh and plants between 250kW and 500kW for 13p/kWh. In addition, biomethane injection into the gas grid will be eligible under the renewable heat incentive for 6.5p/kWh of heat generated.

These incentives proved attractive to Poole-based Aerothermal, an engineering company with 30 years’ experience in the autoclave processing of carbon composites for the motorsport and aerospace industries. Noting the long life of carbon composites and a lack of repeat orders, it decided to diversify and applied its experience to waste. By autoclaving prior to AD, it claims it can take a broader feedstock encompassing municipal solid waste and achieve greater gas yields than similar technologies.

The company is gearing up for a facility near Plymouth that is currently under review by the council and will be able to process 75,000 tonnes of waste per year. Commercial director Tristan Lloyd-Baker hopes it could provide a blueprint for other local authorities. ’The largest facility [would be] about 120,000 [tonnes] maximum. What we’re trying to do is limit the amount of miles waste has to travel, and of course you’ve got issues with byproducts and clean-up, so I don’t think it makes sense to have massive facilities that are shipping waste from miles and miles,’ he said.

Lloyd-Baker added that AD, with certain modification such as his own company’s autoclaving, is the most robust and reliable option in the medium term. ’With any technology, no one’s going to come and buy it until you’ve proved that it does what you’ve told them it will, and there’s no other industry that needs that confirmation more than the waste industry,’ he said. ’There’s a number of plants and technologies that have gone by the wayside that people have invested significant monies in that just haven’t happened.’

But some believe that AD is destined to stay a farm-based application and that there are competing technologies waiting in the wings promising higher yields and efficiency for a lower overall footprint. Swindon-based Advanced Plasma Power (APP) uses two of the competing technologies combining gasification and plasma treatment to break down municipal and tougher commercial waste to produce synthetic gas, or syngas, for heat or power generation.

Interestingly, like Aerothermal it has considerable experience with its core technology through sister company Tetronics, which has been using plasma to treat hazardous waste for around 50 years. ’There isn’t a new technology here; what there is a new process connecting existing technologies,’ said Simon Merriweather, APP chief executive. ’What we ended up doing was using a gasifier as the workhorse it does the hard work of converting the feed into a gas, which then goes into the plasma converter, which effectively cleans it up.’

And it seems some big names agree. British Airways recently teamed up with US-based Solena Group to build a gasification plant that will turn waste into biogas, which will be converted into synthetic kerosene using the Fischer Tropsch chemical process. The plant will take 500,000 tonnes of waste a year from London, including a mix of domestic, agricultural, forestry and industrial feedstocks, and when production begins in 2014 it claims it will produce enough biofuel for all flights from London City Airport.

Evans thinks that if big projects such as this are shown to be successful, it will instil greater confidence in the markets. ’When we start talking about technology risks, bankers just aren’t happy to take it they want somebody else to take it,’ he said. ’With a lot of the projects I see, it’s the financial aspect that holds it up. It will take somebody who is brave and strong willed to drive the uptake, but it can be done.’