Water is a rotter

Research from Ohio State University suggests rubbish in a municipal landfill could decompose nearly 10 to 20 times faster than it normally does using a system that keeps the garbage continuously wet.

Landfills are usually dry environments, and the lack of adequate moisture doesn’t allow biodegradable rubbish to decompose as quickly as it should, said Ann Christy, an assistant professor of food, agricultural and biological engineering at Ohio State.

Keeping a landfill saturated means it could stabilise in five to 10 years, instead of taking the average 100 years or longer to do so, said Christy. The majority of rubbish will have decomposed in a stabilised landfill.

‘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 at as quickly.’

Christy is currently experimenting with moisture levels in two laboratory-scale wet-tomb bioreactors. A wet-tomb bioreactor is a self-contained unit with water purposely pumped into it. The water, which is recirculated throughout the system, creates an environment suitable for bacteria to actively decompose waste.

Christy and her colleagues monitored the experimental bioreactors for 15 months. Each bioreactor – or bin – was filled with approximately1.5 metric tons of non-shredded municipal solid waste collected from a local sanitary landfill.

The waste in one bin was covered with a single layer of sludge, a material composed of sewage already decomposed by bacteria.

At the beginning of the study researchers poured distilled water into each bin until they saw the water draining into the liner under the bins. The used water – or leachate – was continuously pumped through the bins through leachate recirculation pipes.

While the researchers did not get the decomposition results they had hoped for, they are confident that keeping a relatively high level of moisture in a landfill would increase the rate of decomposition, said Christy.

She attributed the lower-than-expected decomposition rates in this study to the lack of adequate amounts of bacteria and also the lack of heat production. Paper and plastic comprised 70 percent of the solid waste in these bins, while readily biodegradable products comprised less than 5 percent of the total mass.

Christy is continuing the experiment, and says the next step is to take the technology to a full-scale landfill.