Several times a year inquiries are received about using a screw press or Fiber Filter for cleaning waste waters in meat processing facilities. Recently we visited a plant that has a very successful system.

The company, Burke Corporation of Nevada, Iowa, is a major producer of meat pizza toppings. Over 1,500 recipes are used to produce 30,000,000 pounds per year of pre-cooked beef and pork, sausage, pepperoni, bacon, meatball, etc. The waste water flow contains large amounts of suspended grease and fat.

Initial treatment is in a conventional DAF where the suspended solids are agglomerated, floated, and skimmed off the surface. The treated water drained from the DAF is low enough in BOD that it is suitable for discharge to the municipal wastewater treatment plant.

The sludge emulsion skimmed from the DAF looks and feels like what would result from mixing hamburger and vegetable oil in a Warring blender for an hour. The sludge has a water content in the high 90% range.

When this sludge is put in a screw press the screen blinds and no throughput flow or solids separation results. If pressure is added by pumping the material into the press with a positive displacement pump, the sludge is simply extruded through the screen in an unchanged condition. A screw press is not suitable for this dewatering application.

Similarly, the fine mesh sleeve of a Fiber Filter is unable to separate any solids from the DAF sludge.

What Burke Corporation does with the sludge is to pump it to a heated tank. Steam is used to heat the emulsion from 200º to 250º F. It is allowed to cool to room temperature, and then it is re-heated. This cycle is repeated many times over a period of days. Eventually a separation occurs. A product that is classified as #2 Grease floats to the top; this is sold as a raw material to a rendering company that refines the grease into other products.

Water is drained from the bottom of the tank. While very dirty, this water is nevertheless suitable for addition to the wastewater stream going to the DAF.