Aerospace Industrial Waste Pretreatment
RALPH STONE, President
HERBERT SMALLWOOD, Project Manager
Ralph Stone and Company, Inc.
Los Angeles, California 90025
INTRODUCTION
Many local pollution control regulatory agencies currently establish requirements for
wastewater discharges prior to issuing a discharge permit. These requirements are typically
based on such factors as the type of industry (Standard Industrial Classification);
wastewater flow and quality parameters; receiving water quality; and the filing of surcharge
statements. Future limitations on industrial water pollution discharges will be far more
restrictive. This is due in large part to the Federal Water Pollution Control Act (FWPCA)
Amendments of 1972. The goal of this significant law is to achieve zero discharge of
pollutants into the Nation's waterways by 1985. A key part of the FWPCA Amendments
calls for a National Pollutant Discharge Elimination System (NPDES) permit. These
discharge permits are being administered oh a plant-by-plant and industry-by-industry
basis, by either States whose permit programs have been approved by the Federal
Environmental Protection Agency, or directly by EPA Regional offices. The NPDES
permit is the mechanism whereby the "best practicable" (1977) and "best available" water
pollution treatment technologies, as identified by the EPA, will be implemented by
industries across the Nation.
The present report assesses the wastewater treatment methods in the aerospace
industry and their ability to achieve the zero discharge goals of the FWPCA Amendments
of 1972. Four specific industrial processes are examined: metal plating, metal finishing,
soluble oil recovery, and brine-zeolite water softening.
For the metal plating and metal finishing wastes, two representative grab samples
each were obtained from a large aircraft manufacturing plant and analyzed in the laboratory. For the soluble oil recovery and water softening processes, estimates of wastewater
constituents were based on available information. Once wastewater composition was
estimated, treatment methods for the four industrial processing steps were analyzed.
Factors considered in these assessments were primarily technological capabilities (i.e.,
ability to achieve zero discharge) and the related economics of treatment vs. disposal.
Treatment method efficiencies and parameters for metal plating and metal finishing
wastes were determined in the laboratory; treatment efficiencies and parameters for the
remaining processes were estimated from the literature.
METAL PLATING
Treatment Methods
The principal metal plating processes consist of chromium, cadmium, nickel, and tin
plating; schematics of these processes and their wastewater treatments are shown in Figures
1, 2 and 3. Treatment of the rinse is provided to precipitate one of four particular metals.
Flow from the treatment station, which is the last rinse step, is by gravity to a sump where a
pump lifts the liquid to a reservoir. The reservoir serves as a settling tank in which the metal
precipitates out. The reservoir also acts as a surge tank for shock waste loads and as the
point for replenishment of the neutralization bath. Replenishment is accomplished by first
mixing a concentrated solution of the bath in a stock tank and then adding the solution to
the reservoir by means of a metering pump.
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