and chemical treatment of mixed waste. Under certain conditions, regulators may allow such activities without a permit or may temporarily waive the storage or treatment permit requirements. Most regulators allow separation or treatment of chemical and radioactive components in the waste collection container or as part of a process without a RCRA permit.

Within the context of these changes, attention is being directed at promising technologies for the treatment of multihazardous waste. At this time, it cannot be determined if and when these technologies will be available, or if they will be developed for use in the laboratory or on a commercial scale. Nevertheless, they deserve careful attention, as do other approaches that will surely be developed in the near future, including the following:

  • Ultraviolet peroxidation is being reviewed by the National Institutes of Health as a method to treat laboratory aqueous mixed waste containing low concentrations of organics. The process, though still under development, is expected to treat a wide range of organics and sterilize the waste.

  • Wet oxidation and supercritical fluid oxidation (for aqueous solutions containing 1 to 10% organics) are being developed to destroy the chemical constituents in mixed waste.

  • Biodegradation has been used successfully to treat soil, sludge, and other contaminated waste streams containing up to 1% organic waste. Laboratory-scale bioreactors are commercially available.

  • Plasma torch, thermal desorption, molten salt pyrolysis, vitrification, and arc or hearth pyrolysis followed by incineration have all been used to treat mixed waste.

7.D PROCEDURES FOR THE LABORATORY-SCALE TREATMENT OF SURPLUS AND WASTE CHEMICALS

Concerns about environmental protection, bans on landfill disposal of waste, and limited access to sewer disposal have encouraged the development of strategies to reduce hazardous waste from laboratories. Many management methods are considered in earlier chapters of this book (see Chapter 4, section 4.B, and Chapter 5, section 5.B). The small-scale treatment and deactivation of products and by-products as part of the experiment plan is one approach that can be used to address the problem at the level of the actual generator, the laboratory worker. However, unless there is a significant reduction in risk by such action, there may be little benefit in carrying out a procedure that will simply produce another kind of waste with similar risks and challenges for disposal. Furthermore, the question of what constitutes "legal" treatment within the laboratory is still unresolved.

Nevertheless, there is often merit for such in-laboratory treatment. Below are some procedures of general use at the laboratory scale. Additional procedures can be found in the earlier edition of this book (Prudent Practices for Disposal of Chemicals from Laboratories; NRC, 1983) and other books listed in the bibliography. More specific procedures for laboratory treatment are increasingly being included in the experimental sections of chemical journals and in publications such as Organic Syntheses and Inorganic Syntheses.

Safety must be the first consideration before undertaking any of the procedures below. The procedures presented here are intended to be carried out only by, or under the direct supervision of, a trained scientist or technologist who understands the chemistry and hazards involved. Appropriate personal protection should be used. With the exception of neutralization, the procedures are intended for application to small quantities, that is, not more than a few hundred grams. Because risks tend to increase exponentially with scale, larger quantities should be treated only in small batches unless a qualified chemist has demonstrated that the procedure can be scaled up safely. The generator must ensure that the procedure eliminates the regulated hazard before the products are disposed of as nonhazardous waste. In addition, if the procedure suggests disposal of the product into the sanitary sewer, this strategy must comply with local regulations.

(See Chapter 6, section 6.F, for further information on protective clothing and also Chapter 5, section 5.C.2.6.)

7.D.1 Acids and Bases

Neutralization of acids and bases (corrosives) is generally exempt from a RCRA treatment permit. However, because the products of the reaction are often disposed of in the sanitary sewer, it is important to ensure that hazardous waste such as toxic metal ions is not a part of the effluent.

In most laboratories, both waste acids and waste bases are generated, and so it is most economical to collect them separately and then neutralize one with the other. If additional acid or base is required, sulfuric or hydrochloric acid and sodium or magnesium hydroxide, respectively, can be used.

If the acid or base is highly concentrated, it is prudent to first dilute it with cold water (adding the acid or base to the water) to a concentration below 10%. Then the acid and base are mixed, and the additional water is slowly added when necessary to cool and dilute the neutralized product. The concentration of neutral salts



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