Dole KP Test
The commercial production of salads has grown exponentially for several years. The original large market was fast food restaurants such as McDonalds and Taco Bell. This has now spread to bagged assortments in the public supermarket.
The factories producing these salads produce huge tonnages of waste material. As much as 30% of the as-received lettuce is scrapped. Most factories sluice the waste with water in floor drains. It goes into pits from which it is pumped with chopper pumps. The flow is run across screens, and the tailings are usually hauled to landfill.
Since these tailings are sopping wet, their disposal presents nasty problems of draining in the parking lot, freezing in the dumpster, and acceptance at landfill. The obvious solution is to run them through a Model KP screw press. However, it has been difficult to close a sale because the press liquor from the press is so loaded with vegetable material that the BOD (Biological Oxygen Demand) is unacceptable to most sewer systems.
In recent months a series of tests have been run at the Soledad, California factory of Dole Fresh Vegetables. Unlike most salad factories, Dole conveys their waste material in a pneumatic system. This greatly reduces the amount of water present.
Testing was done with and without shredder ahead of the presses. Two presses were used: a KP-16 with .095" diameter perforated screen, and a VP-6 with 0.030" perforated screen and a rotating cone option.
The results of BOD measurement are important to note. Despite the wide differences in hole size, only 5% more BOD was measured with the KP. In fact, changes in discharge cone pressure had noticeably more effect on BOD than the hole size.
Physical volume reduction is a goal with Dole. The following results were achieved on cabbage leaves, lettuce and carrot peel:
|Using The Shredder||Not Using The Shredder|
|70% by volume reduction||40% by volume reduction|
|60% by weight reduction||50% by weight reduction|
BOD levels were 20,000 to 22,000 mg/l on the press liquor from shredded material, as compared to 16,000 to 17,000 mg/l without the shredder. These are very high levels, but it must be kept in mind that there was very little wastewater present.
Initially the Dennis Jones Group of Salt Lake City, consulting for Dole, was pleased with these results. It was felt that the BOD would be reduced to an acceptable level by dilution into the plant wastewater stream. However, calculations revealed that this would not be the case. The alternative of hauling the press liquor in tanker trucks for land application also proved uneconomical.
If we are to satisfy the market demand for produce and food disposal equipment, a practical means must be found for disposing of press liquor.
Revision May 1998. Dole Fresh Vegetables is very pleased with the results of the KP-16 at their Springfield, Ohio facility. It is operated with a minimum air pressure on the discharge plate so as to minimize solids in the wastewater. It is felt that the loads of waste material are reduced to one quarter of what they would be without the use of the press.
Later Visit: The plant had raised the air pressure so that fully one half of the waste load was going to the WWTP. This cut the hauls per week in half from what it would be otherwise.