ALUMINUM ANODIZING WASTEWATER
TREATMENT AND REUSE
Roger C. Ward, Project Manager
Howard, Needles, Tammen & Bergendoff
Indianapolis, Indiana 46268
The principal water polluting characteristics of wastewater produced by a manufacturing facdity of anodized aluminum products (Extruded Alloys Corporation, a subsidiary of
International Steel Corp., Bedford, Indiana) are extreme variations in pH and a cloudy
appearance due to inorganic suspended solids. Both highly acidic and alkaline wastewater
properties can exist during a daily operation. The primary source of pollutant load is the
finishing operation of the extruded aluminum products. The wastewater tends to self-
neutralize when captured into a batch volume equivalent to the total daily wastewater
volume. Batch clarification without polymer addition slowly produces a volume of supernatant well in excess of the final sludge volume. Polymer addition accelerates clarification
and produces a high quality supernatant. The minumum sludge volume attainable by batch
settling is not significantly affected by polymer addition.
The wastewater sludge contains high concentrations of aluminum ion which could be a
beneficial source of coagulant to aid in phosphorus removal at a municipal wastewater
treatment plant.
The clear supernatant from batch clarification with polymer addition and without filtration can be recycled to the tank dip and spray rinse steps of the finishing process.
Data for the first nine months of operation for the pH neutralization facility have been
analyzed.
MANUFACTURING PROCESS
The manufacturing process contains four basic operations (Figure 1):
1. extrusion of heated raw aluminum billets into long continuous bars each with a particular cross-section produced by an extrusion die;
2. fabrication of the extruded product into pre-finished parts by cutting, sanding, and
buffing operations;
3. finishing the parts by cleaning, acid polishing or base etching the aluminum surface,
coloring, and anodizing; and
4. shipping the finished product.
A majority of the finished aluminum products are decorative parts for home appliances.
The facility has in the past operated either 10 hours per day, five days per week, or 20
hours per day, seven days per week. Recent operation has been 10 hours per day, five
days per week.
WASTEWATER CHARACTERISTICS
Table I lists the wastewater sources and associated volumes for a typical 10 hour per
day operation. The finishing operation contributes 85% of the hydraulic load and is the
primary source for pH variations and suspended solids. Within the finishing operation,
tap water rinses which follow cleaning, etching and anodizing processes produce 50% of
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