| The National Association of Counties - Washington DC - 3.26.07 |
By Dan Miller – Staff Writer
As old-fashioned landfills continue to pile up and become more and more mountainous, St. Clair County, Mich. has devised a sustainable system to deal with its residents’ trash without continually purchasing land.
The way Morgan Subbarayan, a consultant for the county, puts it, the old model of a landfill was to put down a layer of plastic, pile trash on top and then seal it with another layer of plastic. The result would be that the trash would be trapped in, like a Ziploc bag, in an effort to protect the groundwater. Today, though, Subbarayan says that officials are realizing that the old ways of solid waste disposal are turning into long-term liabilities.
“It’s one of those things where you bury it and it becomes a little mountain in your community and that’s it,” said County Administrator Shaun Groden.
In response to the problem, the county prepared to create a bio-reactor. Traditionally, bioreactors are engineered in such a way that operators can monitor the moisture content and temperature of a disposal site in an effort to expedite the decomposition and gas generation of the trash. According to Subbarayan, bioreactors are a well proven, 30-year-old science.
In a normal landfill, trash decomposes gradually and the volume of gas that emerges is not enough to economically convert into energy. “In a bioreactor, since you are compressing the same volume of gas over a shorter period of time, you’re exponentially increasing the biological reaction,” he said. “[We can] suck the gas out which gives us an opportunity to produce renewable energy.”
As plans went forward to create a bioreactor, Subbarayan and officials in St. Clair County began a lunchtime discussion on the county’s septic waste problem. According to Commissioner Howard Heidemann, the county had been facing illegal discharge of waste and was trying to deal with the environmental consequences when they developed an idea to solve two problems at once.
One element of the process when using a bioreactor is the re-introduction of leachate — liquid at the bottom of the landfill — back into the garbage to expedite the decomposition process. The group’s idea, which Subbarayan calls “spontaneous” and “out-of-the-box,” was to use the septic waste instead of leachate, to make the project a “septate” bioreactor. “Instead of it being a pollutant to our waterways, it becomes a raw material for running the bioreactor,” Heidemann said.
While Subbarayan says there are 13 bioreactors active in the country, St. Clair’s is the only one to use septic waste. “This is the first project in the country where two waste types — liquid waste and solid waste — are married to produce renewable energy,” he said. St. Clair County, which neither exports nor imports trash, paid for the project itself, without grant or loan assistance, by using fees charged for dumping garbage.
The bioreactor’s design also allows for the re-use of different waste sites. Given that there are 10 separate “cells” that trash is dumped into in the bioreactor, the entire landfill operates on a 20-year cycle. After filling each cell, one by one, in 20 years’ time the county hopes the trash will have decomposed at such a rate that the cell will be reusable.
“We’ll be able to go back and use the original, physical site — which is not something you usually do in a landfill,” said Groden. “What this design should enable us to create is a perpetual landfill without the need for continual property purchase.”
Legal roadblocks
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