MIL-HDBK-1005/9A
control, it will affect metals precipitation and metals will be
co-precipitated as hydroxides and sulfides. The metal
precipitates will be separated from wastewater in the oil-water
separation equipment, such as the DAF or IAF. For improved
removal of these precipitates, addition of polyelectrolytes may
be necessary. The laboratory investigation should be conducted
to select the type and amount of polyelectrolyte for
simultaneous suspended solids (metals precipitates) and
emulsified oil removal from wastewater.
3.9.5
Emulsified Oil Treatment. Oily wastewaters contain
varying amounts of emulsified oils and, unlike free oils, simple
gravity settling is not effective for their removal. Formation
of oil emulsions should be minimized as much as possible by
voiding excessive turbulence and the use of detergents or
emulsifying agents. Segregate emulsions for special treatment
wherever possible. Treatment of these segregated emulsions,
which involves oil recovery, is discussed in paragraph 3.10.8.
Emulsions are usually complex, and bench or pilot plant
testing is generally necessary to determine an effective method
for emulsion breaking. Common emulsion-breaking
(demulsification) methods are a combination of physical and
chemical processes. The most common approach to removing
emulsified oils from wastewater is by the use of chemicals.
These emulsions can be broken by chemicals which will balance or
reverse interfacial surface tension, neutralize stabilizing
electrical charges, or precipitate emulsifying agents and cause
flocculation to form larger particles for subsequent removal.
The effectiveness of various chemicals in breaking emulsions must
be determined by laboratory testing. Refer to American Petroleum
Institute (API), Manual on Disposal of Refining Wastes, Volume on
Liquid Wastes for the testing procedure. Coalescence and
flotation separation of oil and water phases follow chemical
addition. Chemicals commonly used include alum, ferrous sulfate,
ferric sulfate, ferric chloride, sodium hydroxide, sulfuric acid,
lime, and polymers. The polymers or polyelectrolytes are large
organic molecules that may be charged (cationic or anionic).
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