Landfills could be 10 to 20 times more efficient

Landfills are not being used to their maximum effect, according to a researcher from Ohio in the USA, whose study suggests that rubbish in municipal landfills could decompose 10 to 20 times faster than it normally does if kept continually wet.

Landfills could stabilise, with the majority of their waste decomposed after only 10 years, if a continuous flow of water through the waste is maintained, says researcher Ann Christy, an assistant professor of food, agricultural and biological engineering at Ohio State University. Currently, traditional landfills take an average of 100 years to stabilise. “Quicker decomposition rates mean more room for more trash in the same landfill, which would cut down on the need for additional landfill space,” said Christy. “This also feeds into recycling – once the biodegradable material decomposes, we can extract recyclables from the landfills, then the landfills aren’t filling up as quickly.”

Christy sees the technology as recycling landfills, rather than filling them up and moving on to a new site, and likens it to the way in which sewage treatment plants treat water, she told edie.

The research was carried out over 15 months, using two ‘wet-tomb bioreactors’, which are self-contained units with leachate constantly circulated through the system, creating a suitable environment for the bacteria essential for decomposition. Each bioreactor was filled with approximately 3,300 pounds (1.5 metric tons) of non-shredded municipal solid waste collected from a local sanitary landfill, with decomposition studied through an observation window.

Unfortunately, the rates of decomposition in the study were far lower than expected, which was probably due to a lack of heat production and to inadequate amounts of bacteria, says Christy. Paper and plastic comprised 70% of the solid waste in these bins, while the two most readily biodegradable products, yard waste and food waste, comprised less than 5% of the total mass.

“The disproportionate amount of recyclables (paper and plastic) in the bins were undoubtedly a hindrance to the bacteria’s success in breaking down the trash,” said Christy. “In a full-size landfill, the types of trash would be more evenly distributed.”

A second generation of bioreactors is currently under construction, Christy told edie, which are made of heavy-duty non-reactive plastic, such as that used for landfill liners, rather than the steel used for the first generation of bins. The future research will be looking specifically at the best ways for recirculating the leachate, with eight different treatments being studies. Other projects being run by the department include a survey of working landfills across the US, and a study of the microbiology of landfills into which organisms are carrying out the bulk of the decomposing.

Though the construction of full-scale wet-tomb bioreactors would require higher costs than traditional landfills, due to the recirculation of the leachate, says Christy, there would be lower running costs associated with leachate treatment required by current landfills.

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