办事指南

What rotten luck - Keeping landfills wet speeds up decay but risks polluting groundwater

点击量:   时间:2017-04-17 02:02:04

By Jeff Hecht Boston RUBBISH decomposes faster if it is kept wet and warm, according to researchers in Wisconsin. The researchers looked at how fast different types of waste decayed, by burying rubbish in a variety of landfills and digging it up later. “Measuring what’s happening in landfills is really difficult,” says Robert Ham, emeritus professor of civil engineering at the University of Wisconsin in Madison. Ham and his students buried the rubbish in open-mesh bags three metres deep in three separate landfills in Florida, Pennsylvania and Wisconsin. They found that the rubbish decomposed fastest in the warm, wet Florida landfill, where three-quarters of the food —by dry weight—decomposed in just two years. In the drier Wisconsin landfill, only two-thirds of the food had rotted away after six years in the ground. Newspapers are not as ephemeral as their readers might think. They do not decay nearly as quickly as office paper. After six years in the ground at Wisconsin, high-cellulose office paper had almost completely decomposed but only 8.5 per cent of newspaper had broken down, says Ham. Newspapers survive because their cellulose fibres are coated in lignin. Office paper lacks this protection. But the main focus of the study, which was sponsored by Procter & Gamble, was to find out how fast disposable nappies would decay in landfills. Experimental nappies made out of pure cellulose decomposed relatively quickly. More than half of them had rotted away after being buried for six years in Wisconsin. However, tests with highly absorbent nappies were less successful. These nappies, which include absorbent gels for “soaking up stuff from baby, did the same in the landfill,” says Ham. One type of nappy even clocked up a net gain in dry weight. Ham says that this was an aberration and the nappy had probably soaked up solids in solution from liquid in the landfill. Although Ham says moisture can get rid of garbage by speeding up its decomposition, government regulations specify that landfills should be kept dry. Al Geswein, a landfill specialist at the Environmental Protection Agency, warns that the result of keeping a landfill wet will be to generate “water with decomposition products in it”. This water could leach out of a landfill and contaminate groundwater. “The number one priority when you’re designing and operating a landfill is to protect groundwater,” says Geswein. The Environment Agency, which licenses landfill sites in England and Wales, says that its rules are tailored to the geology of each individual site. However,