OPTIMIZATION OF HEAVY METALS WASTEWATER TREATMENT
EFFLUENT QUALITY VERSUS SLUDGE TREATMENT
Jack McVaugh, Industrial Process Engineer
William T. Wall, Jr., Industrial Marketing Group Manager
Envirex, Inc.
Waukesha, Wisconsin 53186
INTRODUCTION
In ever-growing numbers industries with wastewater pretreatment facilities are finding
that all problems are not immediately solved when their systems "go on-line." There
must be a "shakedown" period in which the system operation is optimized and operating
personnel become familiar with the flexibility and controllability of their system.   During
this shakedown, operating variables are changed until effluent requirements are met, sometimes giving little attention to how these variables affect the overall operation and economics of the pretreatment facility.
This report concerns an optimization study conducted at the pretreatment facility of
a heavy equipment manufacturer.   The system normally accomplishes greater than 90%
removal of suspended solids, total chrome, iron, lead and zinc.   Average influent concentrations of these pollutants are 200, 26, 56, 8.9 and 42 mg/1, respectively.
BACKGROUND
In March 1975, a wastewater pretreatment facility was installed at a major farm equipment manufacturing plant.   The combined wastewater flow of 100-200 gpm originates
from paint stripping, prepaint washing, nickel-chrome plating, zinc plating, quenching and
dust collecting, as well as compressor and cooling tower blowdown operations.   Treatment consists of primary clarification to remove free oil and settleable solids, pH adjustment by lime addition, solids contact and flocculation, sedimentation for heavy metal
removal, and sludge treatment by gravity thickening and vacuum filtration.
The project was initiated nearly 2 years before, when pollution control studies indicated the magnitude and complexity of the wastewater disposal problem.   Compounding
the problem was a 20-month deadline to have a system on stream.   This deadline dictated
an immediate course of action, and inquiries-whose bid scope defined influent conditions, set effluent standards, and included construction specifications-were issued to
firms with "total systems" capabilities.   By taking this approach, the time requirement
was met, and the responsibility for system performance was clearly defined.   The owner's
internal manpower requirements were minimized as the project coordination, engineering,
purchasing and construction functions were performed by the supplier with approval of
the owner.
The initial task of the supplier was to conduct a plant wastewater survey to verify the
work performed earlier.   All manufacturing processes contributing wastewater were observed and flow rates monitored.   Composite as well as individual grab samples were collected for pollutant evaluation.   Composite samples were also used in laboratory treatability studies, conducted to allow the supplier's process engineers to develop a flow
scheme and to select and size the individual pieces of equipment.   The treatability tests
were designed to approximate full-scale operations, with appropriate scale-up factors,
whenever possible.   The parameters predicted from the results of this testwork are compared to actual operating conditions later in this report.   The flow scheme selected is
shown in Figure 1.
Process design was followed by detailed equipment and tankage design, pump selection, piping design and building layout.   All these were continually developed and modified as the unit processes were refined.   The final layouts and utility requirements were
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