TM 5-814-8
term used to describe treatment of wastewater
poisoning by the iron cyanide complexes.
containing large amounts (2 to 7 percent) of
Wastewater is first passed through a cation
emulsified oils, such as emulsions used in machin-
exchanger to remove metals, breakup complex
ing operations. Cracking involves addition of
metal cyanides, and free the cyanide for removal
chemicals such as sulfuric acid, iron salts, alum,
by the successive anion exchanger. The anion
resin may be regenerated with caustic, recover-
calcium chloride, or proprietary organic com-
pounds, followed by heating to 100 to 140 degrees
ing the cyanide as sodium cyanide. The volume of
F. This is followed by two to four hours of
the recovered cyanide solution is only 10 to 20
coalescence. The effluent may still contain a few
percent of the original waste volume
hundred mg/L of emulsified oil, and should be
(34)(109)(111).
further treated, along with other waste streams
(4) Oil removal. Wastewater from munitions
metal parts manufacturing and flows from air-
having a similar level of oil content, by adding
craft and vehicle washing, paint-stripping and
coagulating salts to lower the oil concentration.
metal-working operations may contain large quan-
Wastewaters with less than 500 to 1000 mg/L of
tities of oils in any of three forms: free floating
emulsified oil, or the effluent from the cracking
oil, emulsified oil or soluble oil. Physical, chemical
step, may be treated by adding iron or aluminum
and biological treatment steps may be used in
sulfate salts, forming a metal hydroxide-oil sludge
various combinations in order to reduce oil con-
(95)(108)(129). A typical treatment scheme is
centrations to levels required by water usage or
shown on figure 6-2.
regulatory criteria.
(c) Soluble oils. Soluble oils, such as certain
(a) Free oils. Free oils readily float to the
animal and vegetable oils, may be readily re-
water surface to be removed by gravity separa-
moved by conventional biological treatment pro-
tors such as conventional primary clarifiers with
cesses (89)( 120). In general, oils derived from
surface skimming devices or separators designed
petroleum are n e i t h e r readily soluble nor
according to American Petroleum Institute (API)
biodegradable, although biological systems can
criteria. The effectiveness of these and other
be developed to provide treatment of some of the
means of removing free oil from wastewater
soluble fractions of petroleum oils. Domestic sew-
varies depending on the type of oil, temperature
age helps to provide inorganic nutrients essential
of the waste, and other factors. As a guide,
for the biological degradation of the high BOD
however, some generalizations can be made. Grav-
oils.
(5) Deep well injection. Pumping waste liq-
ity separation devices are effective in reducing oil
concentrations to about 150 to 200 mg/L. Dis-
uids into deep wells which tap porous rock
formations has been used to dispose of "untreat-
solved air flotation, similar to that used to
able" or hard-to-treat organic and inorganic
thicken sludge, is effective in reducing oil levels
wastes from various industries.
to 50 to 100 mg/L. Granular media filters, pre-
(a) Pretreatment requirements. Wastes
ceded by gravity or flotation separators, can
must be pretreated to remove any suspended
reduce oil concentrations to 10 to 20 mg/L.
solids which could clog the pores of the receiving
Chemical coagulation and precipitation, followed
rock formation. In addition, biological growth
by gravity separation or dissolved air flotation,
(and the resultant slime formation or corrosion)
can remove all but about 5 mg/L of oil
must be inhibited with the addition of biocides.
(95)(129)(156).
Typical pre-injection treatment is costly and in-
oil-in-water or water-in-oil types. The more com-
cludes chemical addition, neutralization, oil re-
mon oil-in-water emulsions are dispersions of tiny
moval, clarification and multi-stage filtration.
droplets or oil suspended in water. Emulsifying
(b) Geological requirements. Careful geol-
agents such as soaps, sulfated oils and alcohols
ogy and soils investigations must be undertaken
to find a deep strata which is confined so that
and various fine particles enhance the stability of
the dispersed oil, preventing the droplets from
waste fluids will never reach a fresh water aquifer
merging together into larger droplets which could
(92). The underground disposal area must also
have satisfactory reservoir storage (107). The
be removed from the water (95). Prepared emul-
sions are used as coolants and lubricants in
waste must not be capable of reaction with the
machining operations. Emulsions are also formed
brine at disposal level to form an insoluble
when oily wastewater comes in contact with
material. Extreme care must be taken in drilling,
steam, soaps, caustic or agitation. The emulsion
constructing, and sealing the well to prevent any
must first be broken, then the oil released is
contamination of groundwater in other subterra-
nean formations (37). Well casings must be highly
removed as a free oil. Emulsion cracking is the
6-30
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