Chapter 17: Solid Waste Management 17.1 Kinds of Solid Waste 17.2 Municipal Solid Waste 17.3 Methods of Waste Disposal

17.1 Kinds of Solid Waste Solid waste is generally made of objects or particles that accumulate on the site where they are produced, as opposed to water and airborne wastes that are carried away from the site of production.  They are typically categorized by the sector of the economy responsible for producing them.

Kinds of Solid Waste Mining wastes are generated in three ways:  Waste material is left on the surface at the mine site (i.e. rocks and soil)  Milling tailings (waste material) are dumped on the land (solid material) or stored in ponds (liquid wastes).  Waste or tailings drainage often contains hazardous materials (i.e. asbestos, lead, radioactive materials). Agricultural waste  Includes waste from raising animals as well as crop and tree harvesting (seeds, straw, stems, peelings).  90% is used as fertilizer or other forms of soil enhancement.

Kinds of Solid Waste Industrial solid waste consists of solid waste other than mining.  Estimated to be between million metric tons annually.  Demolition waste (waste debris from destruction of a building)  Foundry sand (silica-based)  scraps  Sludge  Combustion ash Municipal solid waste (MSW) consists of all the materials people in a region no longer want.  210 million metric tons annually.

17.2 Municipal Solid Waste In modern society, many products are discarded when they are broken or worn out, while others only have a temporary use. Those that have only temporary uses make up the majority of solid waste. The Unites States produces about 210 million metric tons of municipal solid waste annually.  This equates to 2 kg (4.4 lbs) of trash per person per day.  Per capita waste has increased 70% since 1960.

Figure 17_04

Municipal solid waste generation rates

Municipal Solid Waste Nations with a higher standard of living tend to produce more municipal solid waste per person than less-developed countries. Large metropolitan areas have the greatest difficulty dealing with solid waste.

Waste generation and lifestyle

17.3 Methods of Waste Disposal In the past, the favored means of waste disposal was to dump solid wastes outside of city or village limits. To minimize the volume of waste, the dump was often burned. This practice is still employed in remote or sparsely populated areas in the world. It is not acceptable practice from environmental or health perspectives.

Methods of Waste Disposal Five techniques are now used in waste disposal:  Landfills  Incineration  Source reduction  Composting  Recycling

Landfills  A municipal solid waste landfill is typically constructed above an impermeable clay layer, lined with an impermeable membrane.  It includes mechanisms for dealing with liquid and gas materials generated by the contents of the landfill.  Each day’s deposit of fresh garbage is covered with layer of soil to prevent it from blowing around and to discourage animals from scavenging for food.  Traditionally this has been the primary method of waste disposal.  Cheap and convenient  Problems associated with poorly designed landfills have been recognized, and substantial efforts are made to reduce the amount of waste entering landfills.

Landfills New landfills have complex bottom layers to trap contaminant-laden water, called leachate, leaking through the buried trash. The water that leaches though the site must be collected and treated. Monitoring systems are necessary to detect methane gas production and groundwater contamination. In some cases, methane is collected and used to generate electricity. New landfills currently cost up to $1 million per hectare to prepare.

A well-designed modern landfill

Landfills The number of landfills is declining.  Many small landfills that were not meeting regulations have been closed.  Capacity has been reached. New landfills often resisted due to public concerns over groundwater contamination, odors, rodents, and truck traffic (not-in-my-backyard).

Reducing the number of landfills

Incineration Incineration is the process of burning refuse in a controlled manner. Currently, about 15% of U.S. municipal solid waste is incinerated.  Most incinerators are designed to capture heat, which is then used to make steam to produce electricity.  The production of electricity partially offsets disposal costs.  Most incinerators burn unprocessed municipal solid waste. This process is referred to as mass burn technology.

Incineration Incinerators drastically reduce the amount of municipal solid waste.  Up to 90% by volume and 75% by weight. Primary risks of incineration involve air quality problems and toxicity and disposal of ash.  Toxic substances are more concentrated in ash (i.e. lead, mercury, cadmium, arsenic).

Incineration Even with modern pollution controls, small amounts of pollutants are still released into environment. The cost of land and construction for new incinerators are also major concerns facing many communities. Construction costs in North America in 2010 ranged from $50-$400 million. U.S. EPA has not looked favorably on construction of new waste-to-energy facilities. It has encouraged recycling and source reduction as more effective solutions to deal with solid waste.

Disposal methods used in various countries

Mulch Mulch is organic material used to protect areas where the soil is disturbed, or to control growth of unwanted vegetation. Organic materials such as large branches and bark are chopped or shredded into smaller pieces.

Composting Composting is using natural decomposition to transform organic material into compost, a humus- like product with many environmental benefits.  With proper management of air and water, composting can transform large quantities of organic material into compost over a short period of time.  Small-scale composting can be accomplished in the backyard, mixing green materials (grass clippings, vegetable scraps, etc.) and brown materials (dry leaves, twigs, soiled paper towels).

Composting About 3,800 composting facilities are currently in use in the United States. Most municipal programs involve one of three composting methods:  Windrow systems involve placing the compostable materials into long piles or rows. Tractors are used to turn the piles periodically.  Aerated piles are piles of material that have air pumped through them so that no mechanical turning is necessary.  Enclosed vessels in which compostable material is fed into a drum, and the material is mixed and aerated.

Source reduction The simplest way to reduce waste is to prevent it from ever becoming waste in the first place. Source reduction is the practice of designing, manufacturing, purchasing, using and reusing materials so that the amount of waste or its toxicity is reduced.

Source reduction Design changes  Since the 2-liter soft drink bottle (2.4 ounces weight) was introduced in 1977, weight has been reduced by 25% (1.8 ounces).  As a result, 250 million pounds of plastic have been kept out of the waste stream. Manufacturing processes reduce waste and increase efficiency (pay careful attention to leaks, spills, and accidents). Purchasing decisions  Choose reduced packaging waste and plan quantities accordingly (prevent unused surplus materials).

Source reduction Using materials to avoid waste generation  Reduce use of hazardous materials.  Follow label directions carefully and use the smallest amount necessary. Reusing items  Delay or prevent entry of items into waste collection stream (waste exchange: use waste product from one industry as a raw material in another). Most businesses and manufacturers have a strong economic incentive to ensure they get the most from all materials they use.  Any activities that reduce the amount of waste produced, reduce the:  Cost of waste disposal  Amount of raw materials needed  Amount of pollution generated

Recycling Recycling is one of the best environmental success stories of the late 20 th century. In the United States, recycling (including composting) diverted about 30% of solid waste stream from landfills and incinerators in  Benefits:  Resource conservation  Pollution reduction  Energy savings  Job creation  Less need for landfills and incinerators

Recycling percentage for selected materials (2007) and recycling rates from

Recycling Container laws provide an economic incentive to recycle.  Requires a deposit on all reusable beverage containers.  A national “bottle bill” would reduce litter, save energy and money, create jobs, and help conserve natural resources. Mandatory recycling laws provide a statutory incentive to recycle (i.e. laws require that residents separate their recyclables from other trash).

Recycling Curbside recycling provides a convenient way for people to recycle.  In 1990, 1,000 U.S. cities had curbside recycling programs.  In 2009, 11,100 cities had curbside recycling programs.  Cities with curbside recycling tend to have higher recycling rates than cities that lack such programs.

Recycle Bank Recycle Bank was founded in  Families on a garbage route are issued a container with a computer chip. Recyclables are weighed and the family earns points redeemable at merchants like CVS pharmacy.  Recycle Bank launched in Philadelphia in  Recycle rates rose from 7% to 90%.  In 2008 Recycle Bank started a pilot program in N.Y at Columbia University.  Students recycle and claim their points.

Recycling There are many technical and economic problems associated with recycling.  Plastics are recyclable, but technology differs from plastic to plastic.  Milk containers tend to be high-density polyethylene (HDPE), while egg containers are polystyrene (PS), and soft-drink bottles are polyethylene terephthalate (PET).

Increasing amounts of plastic in trash

Recycling The plastics industry is researching new technologies. Economics of recycling are of concern.  Unless demand for products keeps pace with growing supply, recycling programs will face an uncertain future. The long-term success of recycling programs is tied to other economic incentives such as taxing issues, and the development of and demand for products manufactured from recycled materials. Government subsidies artificially lower cost of virgin forest materials compared to recycled materials. Demand for recycled products must grow if recycling is to succeed on a large scale.