TM 5-814-8
--Design special drip pans, high-pressure
(3) Gaging and sampling. Because of the
fog-sprays, air knives and shaking
concentrated processing solutions used and their
mechanisms.
highly variable characteristics, proper wastewater
-- Improve racking procedures and mini-
gaging and sampling is essential in determining
mize overcrowding on the rack to facili-
the characteristics and sources of batch-dumps
tate drainage of process chemicals back
and the resultant peaks. Sampling of effluents
into the chemical tank.
from the individual waste sources can be an
--Increase drainage time over the process
important supplement to end-of-pipe data.
tank or install an empty tank upstream
(4) Environmental impact. The extremes of
from the rinse operation in which the
pH and the high concentrations of heavy metals
process solution can be drained and
and cyanides are extremely toxic to all forms of
returned to the process tank.
life. Fish kills and even fatalities to livestock
Reduce the viscosity of plating agents
have been reported when plating wastes were fed
with either water or heat.
directly to a body of water (34). The accumulation
--Add wetting agents to process solu-
of heavy metals in sediment causes long term
tions to reduce surface tension and
pollution. In addition, toxicity to micro-organisms
facilitate drainage.
retards the self-purification abilities of the receiv-
(b) Plating process changes. Changes in
ing stream.
process or chemicals used can result in a reduced
(5) Treatability. P l a t i n g wastes may be
waste volume, reduced waste strength or a waste
treated by conventional municipal biological pro-
more readily treatable.
w h i c h is
Process/
cesses if sufficient dilution is provided. Otherwise,
chemical changes include the following and should
the extreme toxicity of the waste will seriously
interfere with the biological processes. Just as
be considered in pollution control evaluations:
heavy metals become concentrated in stream
--Eliminate use of breakable containers
sediments, they also accumulate in treatment
for concentrated solutions.
plant sludge and can interfere with subsequent
--Employ a recovery step for metals
biological treatment processes and disposal proce-
from the waste stream. This adds an
dures. Pretreatment of industrial wastes to reduce
economic incentive to cleanup the efflu-
constituents to levels which will be compatible
ent.
with biological treatment is required. Pretreat-
--Recirculate the water used in the fume-
ment requirements for plating wastewater to
scrubber systems.
ensure successful subsequent treatment with do-
--Separate cyanide wastes from chro-
mestic waste may require pilot scale studies
mium bearing and other acid wastes to
(34)(76)(78). The pH control, cyanide destruction
avoid production of lethal hydrocyanic
and heavy metal removal/recovery methods dis-
acid fumes.
cussed in chapter 3 are capable of providing the
--Substitute high-concentration plating
required pretreatment for discharge to a biologi-
solutions for low-concentration solu-
cal treatment system or directly to a receiving
tions, reducing the volume of waste to
body of water. Such treatment may also permit
be treated.
recycling and reuse of the water for some process
--Replace cyanide salt plating solutions
needs. In many cases, it is desirable to integrate
with low cyanide or cyanide-free solu-
the treatment operations into the overall plating
tions.
scheme (33)(109).
--Use counter-current rinse flows rather
d. Washing, paint-stripping and machining.
than using fresh water in all rinses.
Washing and paint stripping of aircraft and land
(c) Plating waste reduction by other means.
vehicles is performed as routine maintenance or in
Good housekeeping steps are important waste
preparation for repairing, overhauling and ma-
reduction practices which should be employed for
chining of a part or component of the aircraft or
all industrial operations; those particularly impor-
vehicle.
tant to plating include the following:
(1) Waste reduction practices. The volume of
--Curb areas which have chronic spillage
washrack and paint-stripping wastewater to be
or leakage problems and divert spills to
treated can be reduced considerably by excluding
a holding tank for treatment.
storm water and by employing practices to reduce
-- Increase inspection and maintenance of
the amount of water used. It is reported that
pipes, valves and fittings to prevent
some U.S. commercial airlines have used hot,
leaks and spills.
rather than cold, water sprays in the paint-
6-24
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