Science

ONE THING is clear. The search is on for alternative ways to dispose of hazardous wastes. The uncertainties associated with traditional shallow land burial of hazardous wastes have made it virtually impossible to locate new hazardous waste landfills in Illinois. So industry must find ways to reduce the volume of hazardous wastes going into existing state-permitted landfills and thereby extend the operating lifetimes of these facilities. At the same time, the burden of liability on industries for the hazardous wastes they produce is driving them to find ways to reduce the hazardous nature of their wastes, especially since some of the hazardous components in their wastes are resistant to natural breakdown when placed in the "security" of landfills. Together, these factors are causing government, industry and academic researchers to seek ways to reduce the volume and hazard of hazardous wastes.

Because hazardous wastes are produced in a wide variety of industries and industrial processes, there are no treatment methods which can be applied to all hazardous wastes. But there are several general approaches that can be applied, alone or in combination, to reduce reliance on landfills or to make the hazardous waste more suitable for disposal in landfills: the bulk or quantity of the waste can be reduced; the level of hazard can be reduced; the waste can be destroyed; or the waste can be treated then reused as a material in its original or in some other application. The treatment processes may be carried out in the industrial production plant through process modification or material substitution, or they may be performed in offsite commercial plants specifically designed for such treatment processes. All treatment processes yield some residues which should be detoxified, stabilized and solidified before disposal in landfills, the ultimate repository for such residues.

Bulk or quantity reduction

The amount of hazardous waste that must be managed can be reduced by three general approaches: modifying the industrial production process so that the amount of waste generated is reduced; keeping hazardous wastes segregated from other wastes; and separating hazardous components from waste mixtures.

Industrial process modifications are generally made in order to increase production efficiencies, to improve the final product or to reduce manufacturing costs; hazardous waste reduction may be a secondary result. Modifications might range from small changes in operational methods, such as changes in temperature or pressure, to major changes, such as new processes, new equipment, different raw materials or different end products. As hazardous waste management becomes more costly, waste reduction will likely become a more important primary goal of process modifications.

Source segregation is probably the easiest and most economical method of reducing the volume of hazardous waste. This approach prevents contamination of large volumes of nonhazardous waste. Source segregation is a waste reduction approach that is widely applicable, especially for large waste generators. However, it may be costly for small firms to implement source segregation efforts. Furthermore, there are disincentives that work against such efforts: For example, it might be less costly for a firm to mix all of its wastes, thus diluting the hazardous components enough to allow discharge of the waste into municipal sewers, and to pay municipal treatment fees rather than to install waste segregation or separation equipment.

There are a variety of physical and chemical methods available for separating components of waste mixtures and removing hazardous constituents. This separation reduces the volume of hazardous waste that must be managed and it also allows for recovery of potentially valuable materials for reuse. For example, the rinse water from metal-finishing operations can be rendered nonhazardous by separating the toxic metals. The water can then be disposed through sewage systems and the metals can be recovered.

There are several common and simple technologies for the physical separation of solid and liquid components of waste streams. In industrial wastewater applications, the primary objective is to remove solid contaminants from wastewater prior to discharge. In solid waste disposal, solid-liquid separation techniques can be used to reduce the volume of waste sludges prior to treatment or disposal. Other physical and chemical methods are available for separating mixtures of liquids and for separating dissolved components from solutions.

Hazard reduction

Several chemical treatment methods can be used to alter the composition of some hazardous wastes in order to produce innocuous or less hazardous wastes. For example, acidic or alkaline corrosive wastes can be neutralized, and certain chlorinated toxic wastes like polychlorinated biphenyls (PCBs) can be detoxified by the chemical removal of chlorine atoms. In most cases, the result of chemical treatment is an aqueous waste stream and solids. The aqueous waste can be discharged to sewage treatment plants, and the solids, mostly in sludge form, must be disposed of in an environmentally sound manner. Current regulations allow disposal of chemical treatment sludges in secure landfills without further stabilization. A safer procedure would be to immobilize the waste by solidifying, encapsulating or chemically fixing the waste before disposal in a landfill. These measures would prevent or greatly reduce the leaching of hazardous substances from the landfill.

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Destruction of wastes

Wastes can be destroyed by various biological or thermal treatment methods. Biological treatment is a generic term applied to processes that use microorganisms to decompose organic wastes into water, carbon dioxide and simple inorganic or organic compounds. Conventional biological treatment methods — activated sludge, trickling filter, aerated lagoon, waste stabilization pond — have been used in municipal waste treatment plants for a long time.

Several innovative biological treatment systems that destroy specific organic hazardous wastes and other contaminants are under development. Microorganisms genetically engineered to act on specific toxic materials have been developed in the laboratory and, in some cases, are ready for field tests. For example, scientists in the laboratory of A. M. Chakrabarty at the University of Illinois Medical Center have developed a bacterial strain that can detoxify the herbicide 2,4,5-T (2,4,5-trichlorophenopyacetic acid) in contaminated soil. While these innovative biological treatment methods promise to be highly cost-effective, there is some resistance by the public to the release of microorganisms into the ecosystem, even if laboratory tests have shown that they attack only specific substances and do not interfere or compete with microorganisms already in soils, water or the air.

The goal of thermal destruction processes is to reduce hazardous wastes to water, carbon dioxide and simple organics. Devices are available to treat different forms of wastes (solid, sludge, liquid, gas) and to operate in varying temperature ranges. Incineration is the most widely used thermal treatment process.

There are many effective incineration technologies available, including some for which there is long experience. But even for these, the necessary design parameters to ensure uniform heat distribution and sufficient time for the wastes to be completely destroyed are not fully understood. And, since it is not yet possible to continuously monitor the operations of an incinerator, there is some uncertainty about the degree of destruction achieved by incineration in practice. Incineration also produces air emissions, ash and some liquid wastes from air pollution scrubbing systems; these by-products must be disposed of properly to avoid environmental contamination.

Reuse

Recovery of useful materials from hazardous process waste streams followed by recycling, can reduce the volume of waste, reduce the cost of hazardous waste management and reduce the cost of raw materials. The technical and economic feasibility of recovery and recycling depends on the composition of the waste stream, the ease with which the components can be separated and the volume of waste generated. For example, inorganic salts can be concentrated from aqueous solutions by evaporation; mixtures of organic liquids can be separated by distillation; solids can be separated from aqueous solutions through filtration. Technologies are available to recover many metals from waste streams — nickel, copper, zinc, tin, cobalt, cadmium, chromic acid. Recovery and recycling may be carried out in the original production plant or may be done at offsite commercial facilities specially designed for recovery and recycling of specific chemicals.

Even wastes that cannot be recycled profitably in-plant or by a commercial recycler might be of some value to another company. For example, an acidic waste of little value to one firm might be useful as a waste neutralizer to another firm which generates alkaline waste. In such circumstances, a waste exchange can be useful. A waste or material exchange is usually a clearinghouse service that facilitates the transfer from one company to another of industrial process wastes, by-products, surplus materials or materials that do not meet specifications. Because of the low value of the materials and the high cost of transportation over long distances, material exchanges are usually regional ventures.

Present status

What is the situation today in Illinois? According to the Illinois Environmental Protection Agency (IEPA) there are only four commercial chemical treatment facilities in the state. These are operating at less than full capacity, even though they are small capacity installations. And the incineration industry in Illinois is operating at 65 to 70 percent capacity. It has been estimated that, nationwide, only about 10 percent of the waste which is amendable to thermal treatment is currently being incinerated. It is likely that that the situation in Illinois is similar. The main reason these alternatives are not used more is that, in most cases, landfilling is the cheapest way to manage wastes. In spite of the fact that landfilling of liquid hazardous wastes will be prohibited as of July 1, 1984, and land disposal of other hazardous wastes will be prohibited as of January 1, 1987, there is no indication that the capacities of the treatment industries are being readied to cope with the impending demand.

Although these landfill prohibitions ought to serve as an incentive for the development of alternatives to land disposal, there is an exception built into the prohibitions which may considerably reduce their strength. The language of the law prohibits disposal in a landfill unless specific authorization is granted by the IEPA, and specific authorization may be granted "only after the generator has reasonably demonstrated that, considering current technological feasibility and economic reasonableness," the hazardous waste cannot be stabilized, recycled or treated to render it nonhazardous. Apparenly, as long as there is no technologically feasible and economically reasonable alternative for a particular waste, it may continue to be land disposed. Therefore, as long as land disposal remains a cheap waste management method, the law provides no real incentive to develop alternative treatment methods which are almost certain to be more expensive in the short term than land disposal.

T. Paul Torda is an American Society of Mechanical Engineers State Legislative Fellow with the Illinois Legislative Council Chicago Science Office. He is emeritus professor in the Department of Mechanics, Mechanical and Aerospace Engineering at the Illinois Institute of Technology.

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