Waste sites could prolong their usefulness while reducing pollution using technology to monitor landfill, according to researchers at the University of Florida.
Although the amount of waste recycled each year is increasing, the majority of household rubbish in countries such as the US and UK is still buried in designated sites and left to rot. When a section is filled, the rubbish is covered over with soil to help prevent odours and discourage vermin.
But around 70 per cent of household rubbish consists of paper, food scraps, cardboard and other organic materials, and covering it with earth prevents rainwater and air from entering. This means that the contents degrade more slowly than they would if exposed.
Researchers from the university’s Florida Centre for Solid and Hazardous Waste Management said that by adding controlled amounts of water and air, as well as liquid produced during decomposition from other landfills, they can aid the growth of bacteria to break down waste and create a bioreactor that quickly reduces the volume of rubbish.
This will allow sites to be topped up at a later date, meaning that the amount of land needed for future disposal of the increasing amount of household waste will be reduced, said Tim Townsend, associate professor of environmental engineering and co-leader of the project.
‘The system will allow us to see how waste behaves over time. The idea is to operate landfill as an engineered treatment facility rather than just covering up waste and waiting to see what happens. It is still the primary method of waste disposal in many countries so this is a substantial problem.’
As well as concerns over the amount of space landfills use, there are also worries that chemicals released as the material breaks down can contaminate local ground water, even if the waste pits are lined, as the lining may also disintegrate over time.
So the bioreactor would force the rubbish to decompose within the first few years when the liner is still in optimum condition. The system could be used on both established and new sites, and would consist of a network of holes drilled into the waste.
While many of these holes would work as wells that allow water and air to be evenly pumped through the material, others would be filled with packs of temperature, gas and pressure sensors. These would allow monitoring teams to see where and when decomposition is occurring, and if methane and other gases are being produced. If so, a flare would burn off the gas before it escapes into the air, though emissions could later be harnessed to generate electricity, said Townsend.
‘Soil and broken-down organic matter could be used as a form of compost, while in the future the system could allow recovery companies to recycle plastics and metals that are currently uneconomic,’ Townsend said. ‘We have to make best use of land, and lack of space will become more pressing in the future.’
Operations at a 13-acre prototype site will start later this spring.
And seams mean green
A UK company developing technology to turn methane from coal beds into a green power source claimed its efforts had been scuppered by the government’s energy policies.
Alkane Energy – which extracts methane from abandoned coal mines – has unveiled its first international project in Germany, where it said the environmental benefits of its process were positively encouraged.
The company said the capture of coal mine methane (CMM) can provide a valuable source of energy and reduce harmful greenhouse gas emissions, but claimed current UK electricity trading arrangements meant its only realistic options lay in continental Europe.
CMM is formed when methane trapped inside layers of coal is released by the mining process.
At working pits, CMM is dealt with as a hazardous waste product and disposed of by the mining company itself.
After a mine is closed, however, a large quantity of CMM remains trapped in the disused shafts and continues to escape into the atmosphere. Methane is viewed as a significant contributor to global warming, with an environmental impact estimated at 20 times that of carbon dioxide.
Alkane maps gas reserves in abandoned pits and applies a vacuum to the former workings. As the pressure decreases inside the mine, methane is desorbed from the coal and can then be channelled to the surface, where an extraction plant processes the gas.
The usable methane is either pumped to an on-site generator for conversion into electricity that can be fed straight into the local grid, or packaged and shipped for industrial use.
Notts-based Alkane has several operational sites at abandoned mines in the east Midlands and Yorkshire.
The company claims that as well as the environmental benefits, its pithead operations can play a significant role in the economic regeneration of former mining areas.
However, it admitted to shareholders that its second year as a publicly-listed company had been ‘particularly difficult.’
Alkane slumped to a £570,000 loss, blaming a slump in UK wholesale energy prices that had made the development of many sites commercially unviable.
It blamed the government for not doing enough to help the development of the fledgling industry compared to the ‘very significant assistance’ on offer to CMM projects from the German authorities.
Power generated by CMM extracted from Alkane’s German operation will fetch a guaranteed price of £46 per MW/h compared to the £17 available under UK electricity trading arrangements.
Alkane said it would focus on potential projects abroad ‘until there is a major shift of UK government policy towards the industry.’
It also plans to explore the possibility of using its technology to extract methane from landfill sites.