Ozone in Apple Processing

The Challenge: To Reduce Flume Water Usage and Keep Tastee Apples Tasty

Apple processors face increasing needs to reduce the risk of spoilage from bacteria, molds and fungi. At the same time they need to conserve water and reduce waster-water disposal costs, particularly the costs associated with high biological oxygen demand (BOD) and suspended solids (SS.) Using ozone to treat the water that conveys and washes the apples can meet the challenge.

The Old Way

Tastee Apple is a privately owned processor of fresh apples, located in Newcomerstown, Ohio. The plant is one of the major packers in the US of caramel apples. These are fresh apples on a stick, which are coated with sweet brown or red caramel and dipped in with chunks of peanuts or coconut. The plant also produces apple juice and apple chips.

Typically, Jonathan or Empire apples arrive from the field or storage rooms in bins, which hold about 950 pounds (430 kg) of apples each. To avoid bruising apples during handling, the plant uses a water flume to float the apples out of the bins, to transport the apples towards a conveyor for further processing, and - at the same time - to wash them. The 2000 gallon (7600 l) flume at Tastee Apple can handle about 40,000 apples per hour.

The recirculating flume water was chlorinated to control microorganisms. It had to be dumped daily, primarily because it accumulated high levels of soil and organics that had been washed off of the apples.

The New Way

In the summer of 1998, the plant decided to improve the quality of the apples shipped to customers and at the same time reduce the use of water and the amound of BOD discharged to the publicly owned treatment works. To get away from chlorine use and to extend the use of the water, the company installed an ozone treatment system in the flume water.

Water is circulated through the flume at about 600 gpm (2300 lpm.) To ozonate the water, a side stream of about 60 gpm (230 lpm) is first filtered through an 80μ filter with intermittent backwash capability. After filtration, gaseous ozone is injected into this side stream. The ozone is generated in a 5 lbs/day (2.3 kg/day) corona discharge unit, which is fed with drier air. After about 10 minutes of exposure to the ozonated water, the apples are conveyed to a size grader, an inspection belt, andand to the equipment that inserts the stick and coats the apples. Three apples are placed together into a display package.

The ozone concentration in the flume water is maintained at about 0.05 to 0.15 ppm. To control the loss of ozone to the environment, the ozone generator generally is adjusted to about 85% capacity. To ensure that the maximum amount of ozone in the air does not exceed the OSHA limit of 0.08 to 0.1 ppm, an ozone detection unit is continuously monitoring the amount of ozone in the environment adjacent to the flume. Excessive amounts of ozone in the air are also readily detectable by the typical sharp smell of ozone.

The Results

No longer is flume water replaced daily. Now the company can reuse the same water for a whole week, saving more than 12,000 gal/week (45,000 l/week.) Since the ozonation system is running 24 hours a day, it is able to reduce the BOD load in the flume water - particularly during the night when apples are not being washed - to less than 50 mg/l.

The ozone treatment reduced the yeast and mold count in the water, resulting in cleaner apples and a longer shelf life for the caramel apples. As a result, fewer complaints of moldy apples have been received. As one more benefit, workers sorting the apples noticed that their rubber gloves remained clean throughout the day and did not build up a sticky coating as had happened prior to ozonation. However, the seals in the bearings of the original conveyor and automatic valve in the filter were not made from ozone resistant material and had to be replaced after a few weeks of operation.

Challenge Test

To obtain a general idea on the performance of the equipment, challenge tests were performed with apples that had been dipped into a yeast suspension of S. cerevisiae and then washed with ozonated water. Each apple was rinsed in 100 ml of sterile water and then a yeast count was taken on this water.

The data show about a two to three log count reduction. Subsequent spraying with super-saturated ozonated water with 1-3 ppm of ozone would further reduce the yeast count.

What Did it Cost?

A five-pound per day ozone generator, pre-filtration system, ozone injector, ozone monitor and ozone destruct unit costs approximately $50,000, not including installation, piping, wiring and labor.

The Role of the Electric Utility

American Electric Power (AEP) provides electric service to Tastee Apple. To help further the use of ozone technology, AEP and EPRI shared the cost of the equipment with the company and helped evaluate the effectiveness of the equipment.