单项选择题

Landfills You have just finished your meal at a fast food restaurant and you throw your uneaten food, food wrappers, drink cups, utensils and napkins into the trash can. You don’’t think about that waste again. On trash pickup day in your neighborhood, you push your can out to the curb, and workers dump the contents into a big truck and haul it away. You don’’t have to think about that waste again, either. But maybe you have wondered, as you watch the trash truck pull away, just where that garbage ends up. Americans generate trash at an astonishing rate of four pounds per day per person, which translates to 600,000 tons per day or 210 million tons per year! This is almost twice as much trash per person as most other major countries. What happens to this trash Some gets recycled (回收利用) or recovered and some is burned, but the majority is buried in landfills. How Much Trash Is Generated Of the 210 million tons of trash, or solid waste, generated in the United States annually, about 56 million tons, or 27 percent, is either recycled (glass, paper products, plastic, metals) or composted (使成堆肥) (yard waste). The remaining trash, which is mostly unrecyclable, is discarded. How Is Trash Disposed of The trash production in the United States has almost tripled since 1960. This trash is handled in various ways. About 27 percent of the trash is recycled or composted, 16 percent is burned and 57 percent is buried in landfills. The amount of trash buried in landfills has doubled since 1960. The United States ranks somewhere in the middle of the major countries (United Kingdom, Canada, Germany, France and Japan) in landfill disposal. The United Kingdom ranks highest, burying about 90 percent of its solid waste in landfills. What Is a Landfill There are two ways to bury trash: Dump—an open hole in the ground where trash is buried and that is full of various animals (rats, mice, birds). (This is most people’’s idea of a landfill!) Landfill—carefully designed structure built into or on top of the ground in which trash is isolated from the surrounding environment (groundwater, air, rain). This isolation is accomplished with a bottom liner and daily covering of soil. Sanitary landfill—landfill that uses a clay liner to isolate the trash from the environment Municipal solid waste (MSW) landfill—landfill that uses a synthetic (plastic) liner to isolate the trash from the environment The purpose of a landfill is to bury the trash in such a way that it will be isolated from groundwater, will be kept dry and will not be in contact with air. Under these conditions, trash will not decompose (腐烂) much. A landfill is not like a compost pile, where the purpose is to bury trash in such a way that it will decompose quickly. Proposing the Landfill For a landfill to be built, the operators have to make sure that they follow certain steps. In most parts of the world, there are regulations that govern where a landfill can be placed and how it can operate. The whole process begins with someone proposing the landfill. In the United States, taking care of trash and building landfills are local government responsibilities. Before a city or other authority can build a landfill, an environmental impact study must be done on the proposed site to determine: - the area of land necessary for the landfill - the composition of the underlying soil and bedrock - the flow of surface water over the site - the impact of the proposed landfill on the local environment and wildlife - the historical value of the proposed site Building the Landfill Once the environmental impact study is complete, the permits are granted and the funds have been raised, then construction begins. First, access roads to the landfill site must be built if they do not already exist. These roads will be used by construction equipment, sanitation (环卫) services and the general public. After roads have been built, digging can begin. In the North Wake County Landfill, the landfill began 10 feet below the road surface. What Happens to Trash in a Landfill Trash put in a landfill will stay there for a very long time. Inside a landfill, there is little oxygen and little moisture. Under these conditions, trash does not break down very rapidly. In fact, when old landfills have been dug up or sampled, 40-year-old newspapers have been found with easily readable print. Landfills are not designed to break down trash, merely to bury it. When a landfill closes, the site, especially the groundwater, must be monitored and maintained for up to 30 years! How Is a Landfill Operated A landfill, such as the North Wake County Landfill, must be open and available every day. Customers are typically municipalities and construction companies, although residents may also use the landfill. Near the entrance of the landfill is a recycling center where residents can drop off recyclable materials (aluminum cans, glass bottles, newspapers and paper products). This helps to reduce the amount of material in the landfill. Some of these materials are banned from landfills by law because they can be recycled. As customers enter the site, their trucks are weighed at the scale house. Customers are charged tipping fees for using the site. The tipping fees vary from $10 to $40 per ton. These fees are used to pay for operation costs. The North Wake County Landfill has an operating budget of approximately $4.5 million, and part of that comes from tipping tees. Along the site, there are drop-off stations for materials that are not wanted or legally banned by the landfill. A multi-material drop-off station is used for tires, motor oil, lead-acid batteries. Some of these materials can be recycled. In addition, there is a household hazardous waste drop-off station for chemicals (paints, pesticides, other chemicals) that are banned from the landfill. These chemicals are disposed of by private companies. Some paints can be recycled and some organic chemicals can be burned in furnaces or power plants. Other structures alongside the landfill are the borrowed area that supplies the soil for the landfill, the runoff collection pond and methane (甲烷) station. Landfills are complicated structures that, when properly designed and managed, serve an important purpose. In the future, new technologies called bioreactors will be used to speed the breakdown of trash in landfills and produce more methane. In most countries the selection of a landfill site is governed by rules and regulations.