Challenge

Timely distribution of fresh poultry to market is the key to success in servicing the fast food chicken business.  Rocco Farms, Inc. of Harrisonburg, Virginia is the country’s fifth largest poultry processing company.  Its chicken operation caters primarily to the northeastern corridor of the country.  Their main chicken processing plant is located in Edinbrug, Virginia, some 50 miles north of Harrisonburg. 

The chicken business, like their turkey operation, is a complete, vertically integrated industry.  Rocco hatcheries provide 100% of the chicks used by their processing plants.  This amounts to more than 35 million birds per year.  Seventy-five percent of their production is consumed by fast food operations.  “Everything has to work in synch to achieve timely distribution, and that takes constant planning for breeding, feeding, processing, sanitation and waste management right on through to pricing and just-in-time delivery,” says Steve Rhodes, Manager of Quality control at Rocco’s chicken Division. 

He notes that traditionally food industry processors have handled their wastewater treatment through the utilization of aerobic lagoons wherever space permitted.  While Rocco’s Turkey Division operates a wastewater chemical pretreatment plant to meet its regulatory requirements, the Chicken Division was advised by its engineering consultants Clean Water Engineering from Bay Castle, Virginia to utilize a biological system.  This was due to the traditional aerobic lagoons already being in place and no problem with available space.  The problem Rocco was experiencing was that their aerobic lagoon discharge was no longer meeting the more stringent standards for Biochemical Oxygen Demand (BOD) and solids discharge Total Suspended Solids (TSS).

Solution

The biological treatment system they installed is an activated sludge processing system.  The whole procedure starts at the processing plant that processes approximately 160,000 birds a day.  The plant consumes an average of 650,000 gallons of fresh water flow daily. 

• Initially the wastewater goes through a pretreatment process that consists of two shaker screens and a revolving screen.
• From there it is pumped into a holding tank and on to an air flotation unit that skims any surface grease.  The wastewater now contains mostly organic material and suspended solids.
• This mixture, which has a BOD level of 400-600 ppm and suspended solids of 400-700 ppm, is pumped up to their large anaerobic lagoon.  This nutrient rich water is attacked by naturally occurring bacteria.  That bacteria goes through its life cycle, feeding on the nutrients in the wastewater, reproducing and dying.  This has the effect of purifying the water.  These organisms form the basis of the sludge that is processed through Rocco’s biological activated sludge system.
• This system draws the oxygen deficient, bacteria laden wastewater down from the anaerobic lagoon to a 1.2 million gallon aeration tank, where a large boom continuously agitates the water and at the same time forces air into the water to aid in nitrification by the microorganisms of the wastewater.  The wastewater from the lagoon has pH factor of about 6.7 – 6.8 and needs to be in the range of 7.5 to achieve the desired nitrification.
• From the aeration tank the water passes to a clarifying tank where the waste material settles out as sludge.  The overflow from the clarifier is pumped through a final chlorine treatment trough and allowed to flow out to a nearby stream.  BOD removal by this process is about 98% and meets regulatory standards. 
• The mixed liquor is pumped back and forth from the clarifier and the aeration tank in a process that continually builds up the concentration of the sludge at the base of the clarifier.  This maintains a sufficient level of sludge to keep the system functioning at an optimum rate. 
• The sludge is then pumped into a holding tank, called the “sludge hotel” between the clarifier and the aeration tank. 
• From there the “mix” is pumped to a sludge tank where a polymer is added to create a sludge floc that is thick and slurry-like.  These suspended solids are the remaining source of problem pollution that requires dewatering to achieve a high dry solids filter cake suitable for disposal at a landfill.

A number of physio-chemical techniques have been used to filter out these organic, insoluble pollutants.  Based upon the successful use of a Siemens filter press in their wastewater treatment plant at their turkey operation, Rocco engineers decided to have the mixed liquor tested and experimented with at the Siemens Water Technologieslaboratory in Holland, Michigan.  Testing with a variety of polymers resulted in producing an acceptable filter cake of approximately 20-25% solids as well as a filtrate that would meet all regulatory standards.  As a result of these tests, Rocco has installed a 1200 mm, 50 cu. ft J-Press® that operates in conjunction with the activated sludge system.

Results

This successful application of using a filter press for organic suspended solids removal is an innovative approach to handling the pollution problem inherent in sludges produced by secondary treatment systems.  The advantages of using this type of device are two-fold:

1. It is the most effective filtration system available for producing clean reusable or dischargeable water.
2. The residual filter cake has a high dry solids content that is non-hazardous and readily transportable to any local landfill.

The economies of using a filter press become evident when you consider the reduced waste sludge that needs to be hauled away to the landfill.  Less to haul and less to dump results in a substantial number of dollars saved every month for Rocco Farm’s Chicken processing operation.