Environmental Problems, Their Causes, and Sustainability 1

What Are the Advantages and Disadvantagesof Burying Solid Waste? A Widely Used LastResortMost of the world’s municipal solid waste is buriedin landfills that will eventually leak toxic liquidsinto the soil and underlying aquifers.About 54% by weight of the MSW in the United Statesis buried in sanitary landfills, compared to 90% in theUnited Kingdom, 80% in Canada, 15% in Japan, and12% in Switzerland. There are two types of landfills.Open dumps are essentially fields or holes in theground where garbage is deposited and sometimescovered with soil. They are rare in developed countriesbut widely used in many developing countries.In newer landfills, called sanitary landfills, solidwastes are spread out in thin layers, compacted, andcovered daily with a fresh layer of clay or plastic foam.Modern state-of-the-art landfills on geologically suitablesites and away from lakes, rivers, floodplains, andaquifer recharge zones are lined with clay and plasticbefore being filled with garbage, as seen in Figure 24-14.Note in the figure that the landfill bottom is coveredwith a second impermeable liner, usually made of severallayers of clay, thick plastic, and sand. This liner collectsleachate (rainwater contaminated as it percolatesthrough the solid waste) and is intended to prevent itsleakage into groundwater. Wells are drilled around thelandfill to monitor any leakage.Collected leachate is pumped from the bottom ofthe landfill, stored in tanks, and sent to a regularsewage treatment plant or an on-site treatment plant.When full, the landfill is covered with clay, sand,gravel, and topsoil to prevent water from seeping in.When landfill is full,layers of soil and clayseal in trashTopsoilSandClayMethane storageand compressorbuildingElectricitygeneratorbuildingLeachatetreatment systemGarbageProbes to detectmethane leaksMethane gasrecovery wellPipes collect explosivemethane gas used as fuelto generate electricityLeachatestorage tankCompactedsolid wasteGroundwatermonitoring wellLeachatemonitoringwellGarbageSandSynthetic linerSandClaySubsoilLeachate pipesClay and plastic liningto prevent leaks; pipescollect leachate frombottom of landfillLeachate pumped upto storage tank forsafe disposalGroundwaterFigure 24-14 Solutions: state-of-the-art sanitary landfill, which is designed to eliminate or minimize environmentalproblems that plague older landfills. Even such state-of-the-art landfills are expected to leak eventually,passing both the effects of contamination and cleanup costs on to future generations. Since 1997, only thisstate-of-the art type of landfill can operate in the United States. As a result, many older and small landfills havebeen closed and replaced with larger local and regional modern landfills.http://biology.brookscole.com/miller14547