Biology 1110 Online
Chapter 17 Summary
Solid waste
The quantities and composition of solid waste differs from region to region and have changed
over time. About 27% of this waste is paper products, food scraps, plastic metal, yard wastes,
and cloth. The U.S. ranks high among the world’s developed countries in per capita waste
production. The waste in the landfills decomposes under generally anaerobic conditions,
releasing large amounts of methane or natural gas. Water percolating through the
accumulated waste picks up a wide variety of chemicals, many which are toxic. This water is
called leachate. To protect groundwater from contamination by leachate, landfills are lined with
plastic and impervious clay. When sanitary landfills are full, they are capped by a thick layer of
clay. Communities have long burned municipal solid waste at high temperatures to reduce its
volume and weight. Incinerators consumed organic matter, and the ash, which was only about
5-6% of the original volume of waste which was landfilled. The United States ranks high
among the world’s countries in per capita generation of MSW, but the total and per capita
waste streams appear to be decreasing. Most MSW is now treated in sanitary landfills that are
designed to prevent pollutants from leaking into groundwater. Modern sanitary landfills are
designed to prevent contamination of groundwater and reduce odors and aesthetic problems.
