78    IMPROVED PRETREATMENT OF METAL FINISHING
WASTEWATERS AT AN ALUMINUM ANTENNAE
MANUFACTURING FACILITY: A CASE HISTORY
Jill C. Watson, Project Engineer
Woodward-Clyde Consultants
Chicago, Illinois 60603
INTRODUCTION
In March 1992, Antennacraft, a Division of Tandy Electronics, commissioned Woodward-Clyde.
Consultants, Inc. to perform a comprehensive engineering evaluation of pretreatment alternatives for
metal finishing wastewaters generated at the company's West Burlington, Iowa plant. This study
concluded that improved effluent quality could be achieved through a combination of production
process modifications (countercurrent rinsing), changes in wastewater treatment process chemistry,
and an upgrade of the existing pretreatment system hardware. Design and installation of new pretreatment system components, including an improved reactor vessel and a programmable logic controller
(PLC) for control of chemical additions, were completed on a fast-track schedule during the summer
of 1992. Since start-up of the modified pretreatment system, the facility has maintained consistent
compliance with municipal sewer discharge limits. This paper presents a case history of the pretreatment project including discussions of: wastewater treatability results, the final upgraded system-
design, capital and operating costs, and regulatory issues.
DESCRIPTION OF MANUFACTURING OPERATIONS
The Antennacraft facility manufactures aluminum television antennas for retail consumer sale. The
plant receives the aluminum stock material, assembles the antennas and applies the finished antenna
with a cosmetic coating prior to packaging and shipment. Production activities include a chemical
conversion coating process that (a) cleans and prepares the aluminum surface, (b) applies a gold-
colored coating to the finished antenna product, and (c) rinses excess coating chemicals from the
finished antenna prior to packaging.
The aluminum coating operation consists of five process tanks used for cleaning, rinsing, and
conversion coating of the preassembled antennas. The assembled antennas and other parts are secured
into bundles and attached to hoists for processing. The five 1,250-gallon process tanks are used in
series. The first tank (Soap Wash Tank) contains an alkaline cleaner used to remove process oils, dirt
and metal debris from the aluminum stock material; the bath is maintained at about 140°F. The Soap
Rinse Tank immediately follows the Wash Tank and is used to remove residual soap and detergent
from the antenna surfaces. The chemical conversion coating is performed in the third tank, the
Chemical Conversion Tank, where coating chemicals and setting agents are used to produce the
"gold" finish coating on the antenna product. The bath is maintained at a pH of 2.0 and approximately 120°F. The Chemical Conversion Tank is followed by two rinse tanks (the Rinse Tank and the
Final Rinse Tank) made up of tap water that removes excess coating chemicals from the aluminum
parts prior to packaging.
WASTEWATER SOURCES
During the initial wastewater characterization study performed in March 1992, the quality and
quantity of wastewater generated at the Antennacraft facility was investigated. Spent wastewaters
from the aluminum coating operation are generated from the batch dumps of the process rinse tanks.
The Soap Wash Tank becomes spent due to the accumulation of oil, grease and aluminum fines and
prevents the proper cleaning of the antennae. Likewise, the Soap Rinse Tank becomes spent from the
buildup of soap and detergents carried over from the Soap Wash Tank. Both of these tanks are batch
dumped approximately once every two weeks, cleaned and returned to service; these operations result
in an estimated discharge of approximately 65,000 gallons per year of spent soap water and soap rinse
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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