Thermal Treatment in the United States
Thermal Treatment in Environmental Law
Incineration (burning wastes at high temperatures) is quite effective in dealing with many types of waste. Although regulators frequently favor incineration, public interest groups and community members are often distressed by the possibility that air contaminants from the incinerator will add to the existing problem. However, air contaminants can be captured and destroyed, provided the incinerator has the proper mechanisms for destruction. Efficiency of incineration depends on the construction of the unit. Heat may also be used to volatilize certain compounds, causing them to leave the waste mixture. Often such action necessitates use of other technology to make sure contaminants don’t escape into the air.
Thermal treatment can also convert some compounds into fuel, or it can melt wastes and trap them in a glasslike matrix. The latter process, called vitrification, can be done in the ground if the situation is favorable. Otherwise, it is completed in equipment similar to that used to create glass.
The purpose of chemical treatment is to chemically alter the waste so it is no longer harmful. In one method, called ion exchange, chemical reactions create new compounds that are less toxic. Dechlorination, a treatment limited in application, removes chlorine atoms by use of chemical reagents. Carbon, often used to absorb certain compounds, is used to capture volatile organic compounds with consistent success. Another way to lower toxicity is to add chemicals that react with the hazardous wastes to neutralize the waste’s harmful qualities.
Wastewater treatment has utilized technology in this classification for some time, and the methods are beneficial in hazardous waste treatment as well. Waste is divided into sizes by screening, air separation, flotation, or magnetic properties. The amount of waste can then be reduced by dewatering, thickening, filtration, and centrifuges. Soil can be cleaned by soil flushing or soil washing, using a washing solution, which adds chemical treatment to the physical one.
Another way to clean soil, vapor extraction, works well with compounds that will become airborne. It is commonly used for gasoline spills. Wells are placed in the ground, air is pumped in, then sucked out and treated before release. To enhance the effectiveness of this technique, heat may be applied, steam may be injected, or the ground may be warmed through radio frequency waves. This technology, too, combines both physical and chemical treatment.
Biological treatment has been used for years to manage wastewater. Microorganisms, either naturally occurring or genetically engineered, eat the waste, transforming it into less harmful waste. Bioreactors used in wastewater treatment include tanks, aeration, and trickling filters. In a trickling filter, the microorganisms are on the filter and the wastewater is forced into contact with them.
Land farming (also called solid phase bioremediation) occurs either on the ground or in shallow tanks. The waste is spread, microorganisms are added, and tilling takes place periodically. A variation of land farming is soil heaping, in which the organisms, nutrients, and air must be injected into a mound of soil. Composting is yet another form of biological treatment.
Biological treatment of hazardous wastes has grown more and more common. Its greatest successes have been scored wastewater treatment and organic compound cleanup, but gasoline and other fuel spills are also effectively treated by using microorganisms. A significant advantage of using microorganisms is that they can often be effective without moving the waste. But the process does require monitoring, because the bugs need nutrients, water, and air, and they generally work best in warm temperatures.
Radioactive or Mixed Waste
Mixed waste consists of both radioactive and nonradioactive wastes. The first step in its treatment is to separate the two. The nonradioactive portion then undergoes appropriate treatment. However, no one has found a way to treat radioactive waste to accelerate its breakdown into normal waste. So the only treatment possibility for the radioactive portion is containment.
Based on “Environment and the Law. A Dictionary”.