Distillation - doe-std-1128-98

DOE-STD-1128-98

8.4.3.5 Distillation

Distillation (including vacuum distillation) is at least conceptually simple.

It removes all but volatile contaminants. In practice, some contaminants

will cause foaming, and evaporator maintenance is often a problem. If

laundry waste or other waste-containing detergents are to be evaporated, it

may be necessary to add an antifoaming compound. Although these are

sometimes effective, they often degrade with heat faster than the detergents

or other compounds causing the foaming. Few evaporators take the product

to dryness, as this often creates a scale build-up. If the evaporator bottoms

are removed as a solution, they must be solidified, usually with some

increase in volume.

8.4.3.6 Purification by Reverse Osmosis

This process is highly effective on relatively pure water streams. The water

is passed through a semipermeable membrane by mechanical pressure,

leaving contaminants behind. The result is generally 80% to 99% of the

influent water released as pure water, with the remainder containing all of

the contaminants. Reverse osmosis has the advantage over ion exchange in

that it will remove nonionic contaminants although these often shorten the

life of the membrane. It is much more energy-efficient than distillation and

requires much less equipment for the same volume of water treated. It is

sometimes used as a "polishing" technique to further treat relatively clean

water.

8.4.3.7 Solidification

Solidification is often a last-resort treatment because, while the other

treatments described reduce the volume of solid waste requiring disposal,

solidification increases it. Nevertheless, it is useful for some waste.

Portland cement is the most common solidification medium for water

solutions, aqueous suspensions, and resins. However, there are other

proprietary materials, including some especially for oils and other organic

compounds.

8.4.3.8 Solvent Extraction

Solvent extraction is used exclusively with organic solvents and involves

mixing the solvent with an immiscible aqueous solution in which the

contaminant is soluble. In this way, the contaminant is transferred to the

aqueous solution for further treatment. (Solvent extraction may also be

used in the other mode, in which the contaminant is transferred to the

organic solvent solution, but this has fewer applications in waste

management.) The organic solution is usually recycled.

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