Municipal Solid Waste

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MUNICIPAL SOLID WASTE

The estimates of North American garbage production are staggering: The average American disposes of over 3.5 kilograms of trash each day, up more than 50 percent since 1970. The health implications of solid waste include the pollutant burden contributed by various forms of waste management (including incineration, composting, etc.). The "green" approach emphasizes the three Rs: reduction, reuse, and recycling. Alternatives such as incineration and landfills are viewed as unhealthful. However, removal of hazardous materials such as mercury-containing batteries by source separation has had substantial success in reducing toxic emissions from incinerators.

There are many ways to collect garbage, and many ways to process it. Landfills and ocean dumping have long been the mainstay of solid waste management, but these are being phased out. Limitation of disposal options has resulted in long-distance transportation of garbage from urban areas to locales where it can still be disposed of.

THE WASTE STREAM

Solid waste comes from various sources. The following are estimated percentages for New York City. Municipal solid waste (residential, institutional, commercial, and industrial): 55 to 60 percent by weight; construction and demolition waste: 15 to 20 percent (hazardous materials such as asbestos should be separated); sewage sludge: 1 to 2 percent; medical waste (including potentially infectious material): 1 to 2 percent; and harbor debris: less than 1 percent. Dredge spoil can make up to 15 to 20 percent of the waste in a coastal city with a harbor. Other forms of waste that can vary by location include agricultural waste, mining waste, and hazardous waste.

Waste streams differ in the following attributes: (1) physical (e.g., compactibility, density); (2) combustion (temperature, residual ash percentage, heat content in BTUs); (3) chemical composition percentage of nitrogen, carbon, oxygen, chlorine; and concentrations of toxic polyaromatic hydrocarbons (PAHs) and metals; (4) potential for recycling various components; and (5) ease of separation.

A comprehensive waste management program must combine a variety of social, transportation, and treatment technologies. Social issues involve the acceptability of particular programs such as mandatory recycling. Components, in order of desirability, include prevention of wastes at the source; reuse, recycling, or composting; energy recovery; and putting in a landfill only those materials not amenable to other strategies. The plan should consider impacts on air quality, water quality, traffic, noise, odor, socioeconomic effects, and community acceptance.

Developing and evaluating a comprehensive waste management system requires confidence that existing health standards are adequately protective, that all components are maintained and operated according to specifications, and that monitoring and enforcement will work.

WASTE TREATMENT

There are more than thirty technological approaches to managing solid waste. One of the most common is incineration, which requires a burner and often a supplemental source of fuel. The temperature and the residence time of the waste in the burner determine the efficiency with which organic matter is converted to carbon. Noncombustible material, particularly metals, accumulate in the ash and must be removed—either to landfills or for incorporation into concrete and other construction products. As organic matter cools in the stack, unwanted products such as dioxins may also form.

Composting allows organic material to undergo biodegradation and photodegradation, resulting in simple organic molecules that can actually be beneficial to the environment.

Recycling and reuse are likely to be effective for those materials that find a ready market. In both the public and private sector, procurement practices can be controlled by fiat or by incentives to minimize waste. Consumer education programs play a large role in reducing waste, particularly in conjunction with community recycling programs. Incentives for source reduction should encourage replacement of disposables with reusable supplies and equipment.

HEALTH RISKS

Health risks involve contamination of soil and water by leachate from landfills and by emissions of toxic materials from incinerators. The latter include particulates; sulfur dioxide and oxides of nitrogen; hydrogen chloride and hydrogen fluoride; carbon monoxide; chlorinated products, including dioxins and furans; metal residues in ash; and volatile organic compounds, including acrolein and phosgene.

POLLUTION CONTROL DEVICES

Standards governing emissions can be health based, but they are often based on technological considerations including the best available control technology (BACT) and the lowest achievable emission rate (LAER). Filters (e.g., baghouses), electrostatic precipitators, scrubbers, and other devices are used to remove metals and volatile material from the stack prior to emission into the environment. Unfortunately, there are very few published data on emissions from which the efficiency of pollution control devices can be documented.

IMPLICATIONS FOR SITING

Regardless of the choice of technology, siting of a facility should take into account certain considerations. Sites should minimize proximity to residential areas, unrelated workplaces, and exposure to sensitive terrestrial and aquatic ecosystems, and they should be of adequate size to minimize exposure to surrounding communities. An adequate distance should be kept from high-rise buildings to reduce the impact on elevated receptor populations, and stack height is also an important element (higher stacks allowing material to dispose further, thereby achieving dilution). Nearby communities should be involved in the earliest stages of planning, including a clear presentation of the cost/benefit and risk/benefit considerations. An assurance of adequate maintenance and safe operation can be backed up by posting a bond with the community, allowing it to monitor a facility and even shut it down under certain circumstances.

Michael Gochfeld

(see also: Community Health; Hazardous Waste; Landfills, Sanitary; Mercury; Not In My Backyard [NIMBY]; Pollution )