The commercial production of salads has grown exponentially for several years. The original large market was fast food restaurants such as McDonald’s and Taco Bell. This has now spread to bagged assortments in the public supermarket.

The factories producing these salads are called fresh cut operations. They produce huge tonnages of waste material. As much as 30% of the as-received lettuce is scrapped. Most facilities [in the 1990’s] 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 operations, 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: