Incineration of wastes
Incineration of waste is a thermal treatment process used to reduce the volume of waste materials, including household and hazardous waste. By subjecting waste to high temperatures, incineration not only diminishes the physical bulk of waste but can also generate energy, particularly through "trash-to-energy" programs. These initiatives have been explored in various regions, particularly in the United States, where the growing problem of landfill space has led some municipalities to consider incineration as a viable alternative. However, the process is not without its challenges; significant public apprehension exists concerning potential environmental impacts, including air pollution and the production of toxic ash, necessitating careful regulation and monitoring.
There are different types of incinerators designed for specific waste types, including grate-type and rotary kiln incinerators, each suited for various waste materials. While hazardous waste incineration is primarily focused on waste volume reduction, energy generation is often a secondary objective. Despite the potential benefits, the high costs of operation and community resistance have hindered the widespread adoption of incineration facilities. Overall, incineration remains a contentious topic, balancing waste management efficiency against environmental and health concerns.
Incineration of wastes
The incineration of wastes provides a means for reducing the volume of various sorts of waste by destroying the organic components of waste.
Background
The incineration of household and hazardous waste material can help to reduce its volume and can provide the potential for electric power generation. The incineration of waste material is not a preferred strategy, however, because it does not stop the depletion of natural resources, and it may cause further environmental problems such as air pollution.
Thermal methods have been developed for dealing with solid, liquid, and the in-between types of waste. Household trash has long been incinerated, often in backyard settings, but many governments now regulate this method except in rural areas. Some cities have built large incinerators for burning solid household waste; these are designed to reduce the waste stream as well as to provide for energy generation. Several types of incinerators have also been developed to deal with hazardous liquid and solid wastes in carefully regulated circumstances. Some of these incinerators have been used for energy production, although not on a large scale.
Household Waste and “Trash-to-Energy” Programs
The large volume of household waste is becoming an increasing problem for many localities in the United States. Landfill space is at a premium in some areas, and incineration offers a means of reducing the waste stream through the destruction of organic material. Open burning is prohibited by the Clean Air Act as well as by many municipal ordinances. However, incineration in grate-type furnaces or kilns can reduce toxic releases to the air, and well-designed facilities can capture the ash for landfilling. This approach involves extensive sorting so that primarily organic material will be incinerated.
Because waste incineration requires high temperatures, a possibility exists for the generation of electrical energy as a by-product of the process. In the late 1970’s and early 1980’s, “trash-to-energy”processes appeared to have a promising future in several U.S. metropolitan areas. Several local governments intended to use incinerators to generate electrical energy, either on their own or in tandem with an electric utility. However, a number of factors hampered the adoption of this approach. There were significant costs involved in sorting waste, and there was public reluctance to accept waste incineration. Landfill fees proved to be cheaper than incineration, and low-cost electric power continued to be available from other sources. Charlotte, North Carolina, for example, adopted a trash-to-energy program in the 1980’s but abandoned it in the early 1990’s as energy costs remained low and the costs of operating the incineration facility continued to increase. According to the Environmental Protection Agency, by the end of 2008, the United States had nearly five hundred landfill-gas-to-energy sites.
Hazardous Waste Incineration
Thermal methods have been a commercial success in dealing with many types of hazardous industrial wastes as well as in cleaning contaminated Superfund sites. The Resource Conservation and Recovery Act regulates the incineration of both liquid and solid hazardous wastes in the United States. Although some municipal incinerators were intended to provide electrical energy as well as reduce the volume of waste, hazardous waste incineration is intended primarily to reduce the waste stream. In only a few cases is energy generation a product of the process, and they usually involve specialized thermal methods such as firing cement kilns with certain types of liquid hazardous waste.
Liquid injection incinerators are the most common type of thermal method for dealing with hazardous waste. As the name implies, this method deals almost exclusively with pumpable liquid wastes. The waste material is injected into the burner or combustion zone of an incinerator through atomizing nozzles. When waste with a low heating value, such as aqueous-organic material, is being incinerated, secondary burners must be used. These incinerators operate at temperature levels from 1,000° to 1,700° Celsius. Residence time for the combustion products ranges from milliseconds to 2.5 seconds. Liquid injection incinerators are carefully regulated as to the type of waste they can burn, the release of gaseous products, and the disposition of the ash.
Three major types of solid waste incinerators exist: grate-type incinerators, hearth-type incinerators, and fluidized bed incinerators.Grate-type incinerators are generally not suitable for hazardous waste incineration because the high temperatures necessary for the decomposition of many hazardous compounds can destroy the grates. There are several types of hearth-type incinerators; the most common are rotary kilns, controlled-air (two-chamber fixed hearth) systems, and multiple-hearth incinerators. The nonslagging type of rotary kiln, often used in the United States, does not require close monitoring, but it also does not have the feed flexibility that a slagging system does. Both types are viable and produce significant energy that can be used to burn additional waste. Multiple-hearth systems were originally designed to handle sewage sludge, but they have been adapted to other circumstances. Fluidized bed technology utilizes a sand or alumina bed sitting on a porous surface. An air flow from below with a carefully controlled velocity places the bed of sand in suspension. Some rotary kilns and fluidized bed systems are portable and have been used to incinerate contaminated soil at Superfund sites and soil contaminated by underground fuel tanks.
Issues of Concern
In the United States, there is a high level of suspicion regarding thermal methods for handling waste materials. This suspicion applies particularly to hazardous waste incinerators, but municipal incinerators are often opposed as well. The public’s worries about safety have helped to curtail the adoption of municipal trash-to-energy facilities in the United States. They have also led to citizen protests regarding local hazardous waste incinerators. Yet the incineration of liquid and solid hazardous organic materials can reduce substantially the amount of hazardous material that needs to be landfilled. Before trash-to-energy incinerators can become fully viable, citizen opposition needs to be reduced, and the costs of operation need to be controlled. Hazardous waste incineration does produce highly toxic ash that requires careful handling, often in specially designed landfills. It is thus not a panacea for curtailing the use of natural resources; rather, it is simply a means of reducing the volume of waste. Throughout the 2010s and 2020s, waste incineration remained a controversial topic among city officials and environmentalists. Though incineration was shown to have negative effects on the health of citizens who live near incineration plants and to contribute to global warming, some areas struggled to find an economical alternative for waste disposal.
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