MIL-HDBK-1005/16
A typical air flotation system is shown in Figure 13.
The removal efficiency of air flotation separators for free oil
is similar to that of gravity separators. However, air flotation
units can also remove dispersed oil droplets in the 40 to 150
micron size range. The addition of coagulants, such as salts of
iron and aluminum with or without organic polyelectrolytes, may
further enhance the effectiveness of the air flotation process in
removing emulsified oil.
Adequate laboratory or pilot studies are necessary, and
adequate justification for the additional maintenance
requirements should be documented before selecting an air-
flotation unit for oil-water separation. Criteria for design of
these units are provided in the EPA Manual 625/1-79-001, Process
Design Manual for Sludge Treatment and Disposal and will not be
described further herein.
5.5.3
Treatment of Emulsified Oil
5.5.3.1
Destabilization. Treatment of oil emulsions is usually
directed toward destabilizing the dispersed oil droplets, causing
them to coalesce and form free oil. The process typically
consists of rapidly mixing coagulant chemicals with the waste-
water, followed by gentle mixing (flocculation). The agglomerated
oil droplets may then be removed by gravity or flotation.
5.5.3.2
Chemical Processes. Alternative chemical emulsion
breaking processes include either the addition of acid (acid
cracking), iron or aluminum salts (coagulation), or chemical
emulsion breakers. In acid cracking, the pH is reduced to
approximately 3 to 4, so the wastewater must be neutralized after
oil-water separation. The use of iron or aluminum salts with or
without polyelectrolytes may be less costly, but produces
additional solids from the chemical precipitates. Proprietary
chemical emulsion breakers are very effective, but they are more
costly than iron or aluminum salts. A number of proprietary
emulsion breakers are available through specialty chemical
suppliers. Different products should be evaluated through bench-
scale tests to determine which is most effective in a particular
application.
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