Pre-Treatment System Removes "Salad Bar" of Contaminants

April 1, 2003
Ken's Steak House Dressings have been famous since they were introduced in 1941. Today, Ken's Foods produces and packages over 400 varieties of dressings and sauces

By Julian Pauwels

The McDonough, GA, facility produces some of the industry's most popular sauces and dressings.
Click here to enlarge image

Ken's Steak House Dressings have been famous since they were introduced in 1941. Today, Ken's Foods — between its Retail Grocery Products and Food Service divisions — produces and packages over 400 varieties of dressings and sauces at plants in Marlborough, MA; McDonough, GA; and soon, in Las Vegas, NV. The following is an overview of Ken's Foods McDonough facilities' pre-treatment solution — from start-up through current phase-two operations.

Pre-Treatment Facility

When the McDonough Plant was built in 1996, USFilter's Davco Division was tabbed by Joel Higginson, President of Advantage Engineering and a consultant to Ken's Foods, to provide a long-term effluent processing system to meet the plant's immediate needs as well as lay the groundwork for an envisioned expansion, three to five years down the road.

The first phase, installed in only eight months to meet plant start-up requirements, was designed to process up to 40,000 gpd immediately and provide the key infrastructure to achieve 80,000 gpd in a later phase.

The McDonough pretreatment facility represents the first time that a Ken's facility had to deal with a wastewater stream requiring treatment of its biological oxygen demand (BOD) levels. For this reason, extensive research and evaluation preceded the final selection of specific process technologies.

"We considered both aerobic and anaerobic options for pretreating the McDonough facility's process wastewater, but decided on the aerobic approach due to economic considerations — specifically the costs of expansion at a later date," Higginson said. "We also factored electrical power and waste disposal costs into the equation before we came to our final decision. Simply, the aerobic process allowed us to minimize the capital investment, gave us the flexibility we needed, and did it economically."

Large Solids Removal

The relatively larger solids that reach the waste stream (vegetable bits, pieces of cheese, and spices) are removed through the use of a hydro-sieve, stationary screen. Following removal of the "screenable" solids, the wastewater is directed to a tank where the free-floating oils are recovered for sale as byproduct.

Instead of having equalization, aeration, sludge digestion and clarification in each tank, the tasks are divided between the tanks.
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"An efficient oil skimming process is important because it not only reduces the load on the downstream dissolved air flotation (DAF) system, but it also provides a byproduct with some residual value," Higginson said.

FOG Removal

According to Don King, Applications Engineering Manager, Davco Products, "The key constituents of a salad dressings plant are salad dressing ingredients — oils, sugars, etc. During processing, many of the fats, oils, and greases (FOG) become emulsified. This typically complicates their removal from the waste stream."

As Dave Muskopf, Vice President of Engineering at Ken's Foods, explains it, "We put a lot of energy into making sure that our emulsified products remain stable emulsions on our customers' tables, then the job of the wastewater pretreatment facility is to demulsify or remove those emulsions from the waste stream."

For this reason, one of the key components of the McDonough pretreatment system is a Davco Dissolved Air Flotation (DAF) unit. This unit, with its powerful separation capabilities, agglomerates the emulsified FOG, which is then removed in a skimming operation.

Equalization Tanks

"After solids straining and skimming of the free-floating oils, the waste stream travels to one of two equalization tanks. Each of the tanks is sized to accommodate a day of process wastewater," King said. "This arrangement allows the waste stream to be evaluated prior to treatment in the DAF. (Note: air is provided to the equalization tanks as a stirring mechanism as well as a way to prevent the development of a septic condition.) This approach creates a homogeneous wastewater stream to feed into the DAF, which helps to minimize the amount of coagulant and flocculant necessary to assist the DAF in removing the emulsified oils. Also, the two tanks are designed with a weir between as a protection against an overflow condition."

Biological Phase

The Davco Dissolved Air Flotation unit agglomerates the emulsified FOG for removal by skimmers.
Click here to enlarge image

The biological phase of treatment is a Davco field-erected "complete-mix" activated sludge system, using circular steel tankage. In 1997, to meet the immediate 40,000 gpd capacity level, the process was designed into a single tank. In 2001, as part of a second phase, pretreatment capacity was elevated to the 80,000 gpd level through the addition of a second tank.

"Originally, we envisioned the addition of a second tank that was a mirror image of the first tank, but as we — the Davco design engineers, Dave Muskopf, and myself — were doing the process engineering on the second tank it became clear that other options would serve the process in a more efficient manner," Higginson said.

"In the end, we decided that rather than having equalization, aeration, sludge digestion, and clarification in each tank, it would be better if we divided the tasks between the tanks. Ultimately, equalization and sludge digestion was segregated to the first tank, and aeration and clarification was designated for the second tank."

It should be noted that the use of steel tankage — with bulkheads that can be altered and relocated — adds significantly to the overall process flexibility. This can be extremely important over the long-term, as needs evolve or change.

"To add operational flexibility, an auxiliary clarifier was added to process filtrate from the sludge-pressing operation. This gave us the added flexibility of pressing and treating at the same time," Higginson said.


Today, the demand for Ken's Foods' products continues to grow. Production is at peak levels at McDonough, and the Las Vegas facility will be coming on-line soon. This kind of growth is only possible when you consistently produce a great product and take specific steps to be a good corporate citizen and — thanks in part to the pretreatment of its wastewater — a good neighbor.

About the Author: Julian Pauwels is Product Line Manager, Filtration, USFilter Davco Products, Thomasville, GA. He received his BSME from the Institute for Higher Technical Studies of Antwerp, Belgium, and has been actively involved in the industry for more than 30 years. Contact Pauwels at: USFilter's Davco Products, 1828 Metcalf Avenue, Thomasville, GA 31792, Phone: 229-227-8742, Fax: 229-228-0312, E-mail: [email protected].

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