A CASE STUDY-TANNERY MEETS EPA PRETREATMENT STANDARDS
Carl V. Huber, Vice President
Thomas A. Doane, Project Manager
Fishbeck, Thompson, Carr, & Huber, Inc.
Grand Rapids, Michigan 49506
INTRODUCTION
Wolverine World Wide, Inc. is a leading pigskin tanner in the United States. Although
it owns and operates many facilities within the nation, the tanning is performed entirely
at its Rockford, Michigan, facdity, located immediately north of Grand Rapids. The tannery
tans approximately 36,288 kg of green salted hides per day with an additional 18,144-
22,680 kg per week of "croupons." The processes performed at the Rockford tannery include the beam house (hair burn), chrome tan, and color and paste. The industrial category
as defined by the Industrial Classification System is 3111.
The tannery practices all beam house operations in one mill rather than separating the
lime-sulfide and chrome tan processes. For this reason, all wastes are generally mixed in the
process sewer and are not conveyed separately.
Table I indicates raw wastewater characteristics. These are general averages for the years
1974 and 1975. Since that date and since the project conception, Wolverine World Wide
has made a successful attempt to conserve water, thereby reducing the flow to the wastewater treatment plant. This, as well as elevated concentrations, wdl appear in later data.
Prior to any expansion, wastewater was rough screened and treated with lime in an area
adjacent to the beam house and then transported by gravity sewer to the waste treatment
plant. Waste traveled through an open grit chamber which was primarily used for removing
large quantities of grease before the wastewater was pumped to the primary clarifier. Prior
to primary clarification, the waste was treated with a coagulant and polymer. This coagulant
was usually ferrous sulfate fed in concentrations of 1000-1500 mg/1. The waste was then
settled in a second clarifier where additional coagulants were added if necessary. Prior to
discharge to the public sewer system in the City of Rockford, caustic was added for pH
control to prevent the formation of hydrogen sulfide (H2S) in the long sewer system to the
City of Grand Rapids.
Sludge was pumped from the underflow of the two clarifiers and conditioned before
being de watered by vacuum filtration. Under normal circumstances, the sludge was conditioned with ferric chloride and lime, de watered to approximately 75% moisture and disposed
of in a nearby landfill. The grease was skimmed not only from the grit chamber but also
from both clarifiers; it was also disposed of in a landfdl (Figure 1).
Table I. Raw Wastewater Characteristics
Average
Minimum
Maximum
Hide Production (kg)
33,566
5,443
48,082
Flow (m3)
1,662
761
2,677
BOD (mg/1)
3,734
2,700
4,600
Suspended Solids (mg/1)
4,806
2,539
8,287
Sulfide (mg/1)
300
100
700
Chrome (mg/1)
82
20
183
Grease (mg/1)
1,000
95