A produce processing company in Tennessee, with assistance from an ozonation system manufacturer in California, has developed an ozonation system for cleaning and sanitizing water used to wash fresh-cut vegetables and lettuce.

It is among the first of its kind to be successfully implemented in a fresh-cut processing plant, and the Ronningen-Petter brand DCF self-cleaning filter is the processor’s filter-of-choice.

Situation
The company processes and packages fresh-cut vegetables and lettuce in bags for the ready-to-eat market. Produce is washed, sanitized and transported through the plant by flume water, which is recycled in a closed loop.

Previous cleaning methods used chlorine to sanitize the flume water, however, the water quickly became discolored and contaminated with suspended solids and chlorine residue. As a result, the flume water had to be replaced every two to three hours.

To improve product quality and conserve water resources, the owner of the company and his team of consultants spent nearly five years developing an ozonated wash system that applied the known benefits of injecting ozone into water as a means of sanitizing the flume water.

His goals were:
1) to obtain a longer shelf life
2) fresher taste and lower bacterial counts for his product
3) reduce the plant’s water consumption

In the original system prototype, coarse suspended solids were removed from the flume water by a rotary screen with a two millimeter gap. It became apparent during initial testing, however, that fine suspended solids also needed removal before ozone was injected — to improve the dissolution of ozone in the flume water.

Ronningen-Petter's Solution
After further design and testing, a new water cleaning and ozonation system was installed, which included two Ronningen-Petter brand DCF Mechanically-Cleaned filters equipped with 50 micron wedge wire screens.

The DCF filters were placed immediately after the coarse rotary screen, to capture fine lettuce particles and prepare the water for ozone injection. The DCF filters perform a self-cleaning action by mechanically scraping collected particles from the filtering screen with a patented disc that moves up and down the screen, parallel to the liquid flow.

Particles are then purged from the collection chamber at the bottom of the filter. This self-cleaning action is performed without halting production, and provides the highest quality filtering under continuous demand. Because the screen is cleaned without interrupting production, a consistently high flow rate is maintained.

Results
Continuous filter: Flume water is cleaned and recycled in an 800 liters-per-minute loop.

Fine filtering: Improves the dissolution of ozone, resulting in dramatically cleaner water, longer run times, and reduced water consumption.

Labor savings: Flume water replacement is required only once a day, instead of every two to three hours.

Ronningen-Petter brand DCF’s continuous filtering capability means the flume water is cleaned and recycled in an 800 liters-per minute loop without interruption.

Its fine filtering improves the dissolution of ozone in the flume water, resulting in:
1. dramatically cleaner flume water
2. longer run times between water changes
3. reduced water consumption.

Now, flume water replacement is required only once a day, instead of every two to three hours. The company owner is also very pleased with the system’s impact on product quality.

His goals of longer product shelf life, fresher taste, lower bacterial counts, and decreased water consumption have been realized.

DCF also provides the additional benefit of improving the performance of a water chiller in the sanitizing system. Immediately after filtering, the flume water is pumped to a chiller where it is cooled to 5°C by spraying the water onto heat exchanger plates.

The high quality filtering provided by the DCF eliminates the risk of suspended solids clogging the sprayer nozzles, and keeps the water chiller at optimum performance.

Conclusion
Ronningen-Petter is pleased that its DCF Mechanically-Cleaned (self-cleaning) filters were chosen as a major component in the innovative sanitizing system developed by the produce processing company.

DCF's continuous and high quality filtration make it the perfect solution for produce washing applications, giving the company improved quality and, ultimately, making their company more competitive.

Application Details
Filter model: (2) Ronningen-Petter brand DCF-1600s
Type of liquid: Wash Water
Pressure: 50 psi (3.4 bar)
Temperature: Chilled
Flow Rate: 211 gpm (47.9 m3/h)
Contaminants removed: Fine vegetable particles and debris