and flammable waste liquids from laboratory operations are almost universally consolidated and used in fuel blending operations, typically to power cement plants. These liquids may also be used as a fuel source for rotary kilns.

8.B.6.2 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. Most sewer disposal is controlled locally, and it is therefore advisable to consult with the POTW to determine what is allowed. Yet, if permitted by the sewer facility, it is often reasonable to consider disposal of some chemical waste materials in the sanitary sewer. These include substances that are water-soluble and those that do not violate the federal prohibitions on disposal of waste materials that interfere with POTW operations or pose a hazard.

Chemicals that may be permissible for sewer disposal include aqueous solutions that readily biode-grade and low-toxicity solutions of inorganic substances. When allowed by law, liquid laboratory wastes that are commonly disposed of in the sanitary sewer include spent buffer solutions, neutralized mineral acids and caustics, and very dilute aqueous solutions of water-soluble organic solvents (e.g., methanol, ethanol). After checking with authorities, some laboratories flush small amounts of water-soluble nontoxic solids into the sanitary sewer with excess water. Examples of potentially sewer-disposable solids include sodium or potassium chloride, nutrients, and other chemicals generally regarded as safe. Disposal of water-miscible flammable liquids in the sewer system is usually severely limited. Water-immiscible chemicals should never go down the drain.

Under federal, state, and local law, there are various exemptions, exclusions, effluent limits, and permitting requirements that may apply to laboratory wastewaters. For most labs, there are allowances for disposing of aqueous waste, rinsate, and certain hazardous and other laboratory wastes (within limits) via the sanitary sewer. Requirements vary by state, locale, and the individual laboratory’s plumbing and sewer system, as well as other facility discharges and treatment systems that the laboratory is part of. Be aware that there are notification requirements for sewer discharges of any acute hazardous waste to a POTW (and more than 15 kg per month of other hazardous waste), and a one-time notification requirement for discharges that fall within the federal domestic sewage exclusion.

In general, if laboratory wastes are discharged via a sanitary sewer to a POTW, follow the advice above to contact your POTW as to permitting and notification requirements and effluent limits. If not, contact your state water pollution control office to determine permitting and notification requirements and effluent limits.

Waste approved for drain disposal should be disposed of only in drains that flow to a POTW, never into a storm drain or 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.

8.B.6.3 Release to the Atmosphere

The release of vapors to the atmosphere, via, for example, open evaporation or laboratory chemical hood effluent, is not an acceptable disposal method. Apparatus for operations expected to release vapors should be equipped with appropriate trapping devices. Although laboratory emissions are not considered a major source under the Clean Air Act, deliberate disposal of materials via evaporation of vapors is strictly prohibited under RCRA.

Chemical hoods, the most common source of laboratory releases to the atmosphere, are designed as safety devices to transport vapors away from laboratory personnel, 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 hood vapors to a common trapping device can completely eliminate discharge into the atmosphere. (See Chapter 9, for more details.)

8.B.6.4 Incineration

Incineration is the most common disposal method for laboratory wastes. Incineration is normally performed in rotary kilns at high temperatures (1200–1400 °F). This technology provides for complete destruction of most organic materials and significantly reduces the volume of residual material which must be disposed of by landfill. However, it is an expensive option, generally requiring the use of significant volumes of fuel to generate the required temperatures. Also, some materials, such as mercury and mercury salts, may not be incinerated because of regulations and limitations of the destruction capability. (For information about reducing the use of mercury in laboratories, see Chapter 5, section 5.B.8.)

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