By Jan TenBruggencate
Advertiser Staff Writer
Several Mainland and foreign areas are experimenting with a new kind of landfill — one that actively composts trash in one-tenth or less the time of a standard landfill.
The primary benefits are two: The landfills produce methane, which can be used as fuel to produce power, and the breakdown of organic materials shrinks the trash, making more room. Thus, landfills last a lot longer.
The idea has been around for a few years. Landfills built and managed in this way are called bioreactors.
They are designed so that liquids that seep through the garbage, called leachate, are collected at the bottom and pumped back up to the top. Bioreactors are kept more moist than a standard landfill. Air can be pumped into them for aerobic decomposition, or they can be kept without air for anaerobic decomposition.
"The addition and movement of moisture to the interior of the landfill creates an environment in which naturally occurring microbes degrade the waste at a much greater rate than they normally would," said a report by the Florida Center For Solid and Hazardous Waste Management.
In Denmark, officials generally ship paper and other burnables to a facility like Honolulu’s garbage-to-energy plant, but where that is not possible for environmental or other reasons, they use bioreactors.
Even nonbioreactors produce methane, but at a lower rate over a longer period of time.
The Kapa‘a Landfill is closed, but the city and county of Honolulu expect to continue collecting methane from it for another two decades. The gas is used as fuel to produce electricity, and the sale of the power makes the city $4,500 to $6,000 a month, said Frank Doyle, chief of the city’s Division of Refuse Collection and Disposal.
Researchers say that fully composted trash in a bioreactor can be mined for the composted soil, which can be used to improve the fertility of planted areas. Once the soil is sifted, remaining nonbiodegradable materials can be put into landfills again or removed for recycling.
Bioreactor landfills have been around for just a few years, and scientists are still experimenting with techniques for making them work most efficiently.
"It’s cutting-edge technology," said Kaua‘i County solid waste coordinator Troy Tanigawa.
Doyle said that bioreactors may not be the best technology for Hawai‘i, where much of the biodegradable material is already removed for garbage-to-energy burning and for large-scale composting.
Too, Hawai‘i’s mountainous topography makes it difficult to create the wide, narrow bioreactor "cells" that work best, he said.
"This is perfect for a flat place, like Florida," he said.
Jan TenBruggencate is The Advertiser’s Kaua‘i bureau chief, and its science and environment writer. You can call him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.
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