generation. That has not happened. Several factors, including the cost of development and concern about how regulatory agencies would view this kind of "treatment," surely have contributed to the lack of progress. A changing regulatory environment could provide a favorable basis for development of such thermal treatment systems.

7.B.6.2 Disposal in the Normal Trash

Laboratory workers may be surprised to learn the number of wastes they generate that can be disposed of in the normal trash. However, because the disposal of trash from households and businesses is normally controlled by the local municipality, the local agency should be approached to establish what is allowed.

When disposing of chemicals in the normal trash, certain precautions should be observed. Because custodians, who usually empty the trash containers, are not usually familiar with laboratory operations, no objects that could cause harm to them should be disposed of in those containers. Such objects include containers of chemicals, unless they are overpacked to avoid breakage, and powders, unless they are in closed containers. Free-flowing liquids are usually prohibited. Sharp metal and broken glassware, even though they may be considered nonhazardous trash, should be collected in specially marked containers, never in the normal trash baskets.

7.B.6.3 Disposal in the Sanitary Sewer

Disposal in the sewer system (down the drain) had been a common method of waste disposal until recent years. However, environmental concerns, the viability of publicly owned treatment works (POTW), and a changing disposal culture have changed that custom markedly. In fact, many industrial and academic laboratory facilities have completely eliminated sewer disposal. Again, like trash disposal, most sewer disposal is controlled locally, and it is therefore advisable to consult with the POTW to determine what is allowed. Yet, it is often reasonable to consider disposal of some chemical waste materials in the sanitary sewer. These include substances that are water-soluble, that do not violate the federal prohibitions on disposal of waste materials that interfere with POTW operations or pose a hazard, and that are allowed by the local sewer facility.

Chemicals that may be permissible for sewer disposal include aqueous solutions that readily biodegrade and low-toxicity solutions of inorganic substances. Water-miscible flammable liquids are frequently prohibited from disposal in the sewer system. Water-immiscible chemicals should never go down the drain.

Disposal of regulated hazardous waste into the sanitary sewer is allowed only in limited situations. The total wastewater must be a mixture of domestic sewage along with the waste whose amount and concentration meet the regulations and limits of the POTW. If approved of by the local district, it may be allowable to dispose of dilute solutions of metals and other hazardous chemicals into the sanitary sewer.

Under the Clean Water Act, some exemption from regulation as a hazardous waste for wastewater containing laboratory-generated listed waste is allowed. In 1993, this exemption was expanded to include corrosive and ignitable wastes. For the exemption to apply, these laboratory wastes must be 1% or less of the annual total wastewater quantity reaching the facility's headworks or have an annualized average concentration of no more than 1 part per million (ppm) of the wastewater generated by the facility.

Waste should be disposed of in drains that flow to a POTW, never into a storm drain and seldom into a septic system. Waste should be flushed with at least a 100-fold excess of water, and the facility's wastewater effluent should be checked periodically to ensure that concentration limits are not being exceeded.

7.B.6.4 Release to the Atmosphere

The release of vapors to the atmosphere, via, for example, open evaporation or fume hood effluent, is not an acceptable disposal method. Apparatus for operations expected to release vapors should be equipped with appropriate trapping devices. Although the disposition of laboratories under the Clean Air Act is not established at this time, it is reasonable to expect that releases to the atmosphere will be controlled.

Fume hoods, the most common source of laboratory releases to the atmosphere, are designed as safety devices to transport vapors away from the laboratory in case of an emergency, not as a routine means for volatile waste disposal. Units containing absorbent filters have been introduced into some laboratories, but have limited absorbing capacity. Redirection of fume hood vapors to a common trapping device can completely eliminate discharge into the atmosphere. (See Chapter 8, sections 8.C.11 and 8.C.12, for more detail.)

7.B.7 Disposal of Nonhazardous and Nonregulated Waste

Many laboratories do not distinguish between waste that is hazardous and waste that neither poses a hazard

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