65    AEROBIC CONTACT PRETREATMENT OF
SLAUGHTERHOUSE WASTEWATER
Michael N. Macaulay, Associate
Terry W. Stebor,Senior Project Engineer
Craig L. Berndt, Manager
Process Engineering
Foth & Van Dyke and Associates, Inc.
Green Bay, Wisconson 54307
INTRODUCTION
Packerland Packing Company, Inc., a high volume beef processor, currently maintains the following primary and secondary production activities at its Green Bay, Wisconsin facility:
• Beef processing at a rate of 265 head per hour, mostly Holstein-type feeder cattle.
• Hide cleaning and curing
• Casing production for sausage producers.
• Tripe production for export sales
• Rendering for high quality tallow production.
• Scrap meat and by-product processing for pet food.
Production wastewater streams were previously pretreared with dissolved air flotation (DAF) followed by chemical conditioning and additional secondary dissolved air flotation. Flotation tank
skimmings were dewatered by vacuum filtration and land applied. DAF effluent was discharged to
the City of Green Bay municipal sanitary sewer with final treatment at the Green Bay Metropolitan
Sewerage District treatment facility.
The primary sources of wastewater flow include the following:
• Washings from the kill floor.
• Washwater from intestine flushing and casing production.
• Paunch liquor from processing stomach contents.
• Tripe wash.
• Rendering plant wastewater.
These sources together constitute the majority of the raw process wastewater. Two additional
wastestreams, the rendering plant air scrubber and the sanitary wastes, are discharged directly to the
municipal sewer. Sewer charges for pretreated wastewater and sanitary effluents are assessed on the
basis of BOD5, suspended solids and phosphorus concentrations. As much as 80% of the monthly
charge can be attributed to surcharges for excess organic loading.
As of mid 1984, Packerland was faced with significant operating costs associated with maintenance
of its pretreatment plant and uncertain disposal opportunities for its semi-solid residuals (Pretreatment plant sludge, paunch solids). In addition, the company was contemplating expansion of its
production and perceived limitations with regard to pretreatment of increased wastewater volume.
Consequently, Packerland sponsored a study of potential treatment system improvements.
The study exposed a list of major deficiencies in the wastewater pretreatment system at Packerland.
These included:
• A long detention time and low surface overflow rate in the existing flotation units
encouraged settling of solids. The primary solids removal mechanism would have desirably been flotation.
• Ferrous sulfate and polymer addition were causing settleable floe to form, resulting in
large volumes of settleable sludge in the flotation units.
• Mechanical design of the flotation units did not provide for settled sludge removal,
requiring manual cleaning on a weekly basis.
647