Lesson: Waste Management (corresponding to Chapter 15: Waste Management & Geology)

Transcription

1 Lesson: Waste Management (corresponding to Chapter 15: Waste Management & Geology) Human society produces waste, and lots of it. That waste gets disposed of in the earth. As the human population (and the waste it produces) grows, the issue of how and where to dispose of our waste becomes more acute. The photo shows an innovative way to deal with the millions of worn out tires produced each year: some of them can be turned into children s playground toys!

2 Summary of Important Concepts There are two main methods for disposing of wastes: 1. Isolation: removing the waste from the environment in some way, usually by burial or by sealing it off (encapsulation). 2. Attenuation: getting rid of the waste by diluting it, incinerating it, or spreading it out thinly over a large area. Three major waste issues will be considered in this lesson: 1. Municipal Waste Disposal - disposing of waste produced by construction, commercial activities, and residential activities in cities and towns. 2. Hazardous Waste Disposal - disposing of toxic fluid or solid substances. 3. Wastewater Treatment - cleaning up dirty water so it can be used again.

3 Summary of Important Concepts, continued MUNICIPAL WASTE DISPOSAL The sanitary landfill is the main system of municipal waste disposal today. In a modern sanitary landfill, each day s waste is covered over and sealed off. When the landfill is full it is covered, graded for drainage, and leachate (polluted water seeping from the landfill) is prevented from contaminating ground water. Different classes (I, II, and III) of landfills indicate the kinds of substances that they can hold safely. Class ratings reflect how well leachate is prevented from polluting local water supplies. Incineration is an alternative to landfills, and is sometimes used in areas of high population density. Ocean dumping was once a common method of municipal waste disposal but is no longer due to strict environmental laws.

4 Summary of Important Concepts, continued The main problems associated with landfills: settlement: caused by biodegradation of waste and compaction; may cause cracks and ponds, allowing water to sink into the landfill, adding to leachate formation gas generation: methane gas caused by biodegradation; can be explosive if not contained; collected by pipes within the landfill and then burned leachate: contained by impermeable barriers of plastic or clay at the base of the landfill, collected by a system of pipes and treated Reduction of waste for landfills can be accomplished by recycling, composting, and various waste reduction strategies. Full landfills can be converted into recreational, commercial, or residential areas.

5 Summary of Important Concepts, continued HAZARDOUS WASTE DISPOSAL A secure landfill that can handle hazardous waste: is lined with plastic and an impermeable clay layer to prevent leachate (toxic fluids) from seeping into the ground contains drains to collect leachate Deep well injection involves pumping hazardous fluid waste deep underground into permeable rock formations that are sealed off by impermeable rock layers. CERCLA (Superfund) legislation was passed in 1980 to hold financially responsible those who have created hazardous toxic waste sites in the past.

6 Summary of Important Concepts, continued WASTEWATER TREATMENT Wastewater is treated at special plants to clarify and purify it to various levels. - primary treatment: removes solids from the water by settling and aeration - secondary treatment: microorganisms (bacteria) are used to remove organic material - tertiary treatment: inorganic dissolved materials such and nitrates and phosphates are removed Biological oxygen demand (BOD) is a measure of the purity of treated water. The more organic material in the water, the greater the demand for oxygen by microorganisms. The cleaner the water, the lower the BOD.

7 Society creates a great deal of waste. Disposing of it properly is an important responsibility. Water purity, air quality, public health, and the quality of our scenery depend on getting rid of waste in an effective manner. Good waste management involves not only waste disposal, but reduction of the amount of waste we produce. There are two main methods for disposing of wastes: 1. Isolation: removing the waste from the environment in some way, usually by burial or by sealing it off (encapsulation). 2. Attenuation: getting rid of the waste by diluting it, incinerating it, or spreading it out thinly over a large area. In this lesson we will be primarily concerned with isolation methods -- the most common way to get rid of waste.

8 Municipal Waste Disposal Municipal waste is the waste produced by construction, commercial activities, and residential activities in cities and towns. The figure below shows the components of typical municipal waste by sector of the economy (on the right) and by type of material (on the left).

9 Sanitary Landfills Until fairly recently, many cities and towns had open dumps where trash simply piled up. The trash stank, attracted vermin, and polluted the ground water when rain washed toxic substances out of the waste. Today such open dumps are being replaced with cleaner and safer disposal areas called sanitary landfills. In a sanitary landfill, every day the waste is: - spread out in thin layers and compacted - covered over and buried by a layer of soil Once a sanitary landfill is full, it is sealed off with a thicker layer of soil, and the surface is graded to a gentle slope to allow water to drain off, preventing water seepage into the landfill. Water infiltration must be prevented in order to stop leachate polluted water that leaks out of landfills from forming. Prevention of leachate is a major concern in modern waste management methods.

10 This figure shows how in a modern sanitary landfill each day s accumulated trash is compacted and covered over with a 6 inch soil layer, sealing it off from the surface.

11 As a modern sanitary landfill is filled to capacity, a final thicker soil layer (shown at left) is applied. The entire area is graded to allow water to flow off the surface. Any leachate (polluted water) that does seep from the landfill goes into a leachate collection system to be disposed of properly.

12 This photograph shows a full, graded sanitary landfill similar to the diagram shown on the last slide. The surfaces will be planted to reduce erosion and make it visually more attractive.

13 Classes of Landfills Landfill are ranked into three classes (Class III, II, and I) based on local geology and the potential for leachate to leak into local ground water or surface water supplies. CLASS III landfills (illustrated above) have no barriers to leachate leaking out, and may even intersect the water table. Class III landfills can therefore hold only non-water-soluble, non-decomposable, inert material (e.g. concrete, rubber products, slag, glass).

14 CLASS II landfills (illustrated above) are isolated somewhat from groundwater supplies, either by natural barriers (like an impermeable clay layer), or by artificial barriers that considerably reduce leachate migration away from the site. Class II landfills can hold most normal garbage, including cans, paper products, cloth, wood, yard clippings, and small amounts of dead animal material, as well as anything that can go in a Class III landfill.

15 CLASS I landfills (illustrated above) are the most isolated from groundwater. Leachate is fully contained by an impermeable liner (clay or plastic), and the surrounding geology also has low permeability. The landfill is not near any water sources, and is in no danger of flood or washout. Class I landfills can hold toxic substances, such as chemicals, toilet wastes, pesticides, fertilizers, and other nasty materials. Class I fills can also hold anything that could go in a Class II or III landfill.

16 Problems of Landfills As waste in a landfill decomposes, the landfill begins to settle (the surface sinks downward), gas is produced, and water in the landfill may create and/or pick up toxic substances, forming leachate. The three main problems of landfills are settlement, gas generation, and leachate containment. Settlement Landfills settle by inches or even a few feet per year as trash decomposes and compacts under its own weight. This causes problems in that cracks and sags (low spots) may form on the surface, which allow water to seep into the landfill rather than run off the surface. These problems must be fixed regularly so that water infiltration is prevented.

17 In addition to causing problems of water infiltration, settlement can also damage structures built on the landfill, as shown in this photo. Settlement does have one advantage: it makes more room for trash!

18 Gas Generation As microorganisms break down landfill wastes a process called biodegradation they produce gas. Biodegradation is useful; it reduces the volume of trash in the landfill, making room for more. Many landfills use a process called composting pumping air down into the landfill to encourage the growth of decomposing aerobic bacteria. The main gas produced by biodegradation is methane (CH 4 ), which is the main component of natural gas. Methane migrates upward through landfills and seeps out, creating dangerous situations. (At concentrations of about 5% in air methane can explode if lighted.) Methane is extracted by sinking perforated plastic pipes into the landfill. The gas is piped away and either sold or used on site to generate electricity. Power from waste!

19 The photo shows a methane extraction well being installed in a landfill. The pipe (perforated at depth) will collect the gas and take it to be burned and generate electricity.

20 Leachate The figure here illustrates how leachate seeping from a landfill could contaminate local water supplies. Leachate containment is a top priority in landfill management today. Recall the information earlier in the lesson about the different landfill classes (I, II, and III). The class indicates the degree of leachate containment.

21 The main method of leachate containment is to put impermeable barriers of plastic and/or clay at the base of the landfill. In the stateof-the-art landfill design shown here, there is a double lining of clay and plastic layers at the base of the landfill, and the leachate that collects there is siphoned off into pipes and taken to treatment areas. Since 1996 federal law requires that all landfills be designed with double liners to protect the environment from leachate.

22 Other Municipal Waste Disposal Methods Landfills are the most common way of dealing with municipal waste. Two other methods are. Incineration: Burning waste has the advantage of reducing the volume of trash produced, and the heat can be used for electrical generation. However incineration is costly, and the pollutants and ash produced need to be dealt with. Incineration is most commonly used in crowded urban regions where there is little room for landfills. Ocean dumping was once a very common method of waste disposal, particularly of sewage. The adverse effects of sewage disposal in the oceans lead to the Ocean Dumping Ban of 1988, which terminated oceanic disposal of raw sewage in the U.S.. Since the ban, coastal communities must process their sewage, putting only treated sewage water in the ocean, disposing of remaining sludge in landfills. Ocean dumping of sewage continues in some countries with less restrictive environmental laws.

23 Reducing Municipal Waste by Recycling Reducing the total amount of waste our society produces can help immensely with waste disposal problems. Recycling programs are growing rapidly across the U.S.. Recycling of paper products is especially helpful, since the majority of landfill waste by weight is in paper (diagram at left).

24 The Concept of Multiple Land Use Most people might feel that once an area has become a landfill, it is off limits to other human use. Not so. As our population and the sizes of our urban areas grows, it is important to think creatively about putting completed landfill areas to other uses. In different parts of the U.S., landfills have been converted to parkland or even residential and commercial building areas. The photograph shows a landfill in Santa Monica, CA, that has been converted into a golf course!

25 This photograph shows a commercial development built on a landfill. To deal with settlement, the buildings are placed on deep columns that go through the fill to the bedrock beneath. Gas generation is put to good use the methane collected from the landfill is used to fuel the lanterns!

26 Hazardous Waste Disposal Hazardous wastes are toxic substances produced primarily by industries. These include sludges, solvents, acids, pesticides, and various corrosive and/or reactive materials. The figure show us the amounts of various classes of toxic wastes produced in the U.S..

27 There are two main methods of disposing of hazardous wastes: 1. Secure landfills. A landfill that can completely isolate the waste from the environment is considered secure. In the landfill classification described earlier in this lesson, these would be Class I landfills. Such landfills have: linings of plastic and impermeable clay to prevent leachate contamination of ground water drainsto collect leachate 2. Deep well injection. Hazardous fluid waste is pumped deep underground into permeable rock formations that are sealed off from groundwater supplies by impermeable rock layers. Before deep well injection can take place, thorough studies of underground geology must demonstrate that the waste is unlikely to leak out and contaminate groundwater supplies.

28 The concept of deep well injection is shown here. The waste is pumped below areas where ground water exists, into porous rock layers which are sealed off from ground water by impermeable rock layers. The pipe is lined with steel to prevent leakage on the way down. Problems: -- the waste may find ways to leak up to ground water supplies -- the waste may leak out through the piping system on its way down

29 Hazardous Waste Legislation Since 1976, disposal of hazardous waste has been regulated by the Resource Conservation and Recovery Act (RCRA). Prior to that there was little regulation, with the result that there are many toxic waste sites in the U.S. that have caused serious contamination and human health problems. The community of Love Canal, NY, is one famous example (see Case Study 15.5 in the book). In response to the hazards of old, abandoned hazardous waste disposal sites in the U.S., Congress in 1980 passed the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also known as Superfund. The key idea behind Superfund is that the EPA can clean up polluted sites and bill the costs of cleanup to those originally responsible. Superfund has cleaned up many contaminated sites. Unfortunately, about 40% of Superfund s money goes not to cleanup costs, but to paying legal bills involved in convicting the original polluters!

30 Wastewater Treatment Law requires that sewage wastewater be treated at special plants to clarify and purify it before it can be disposed of or used. - Primary treatment: removes solids from the water by settling and aeration. - Secondary treatment: microorganisms (bacteria) are used to remove organic material. - Tertiary treatment: inorganic dissolved materials are removed, particularly nitrogen and phosphorous. Tertiary treatment produces water pure enough for human consumption. Biological oxygen demand (BOD) is a measure of how pure treated water is. The more organic material in the water, the greater the demand for oxygen by microorganisms eating the organic material. The cleaner the water, the lower the BOD. Pure water has a BOD of zero.