Membrane System Helps Clean Up Sugary Wash Water

In processing about 200 tons of raisins daily with its "Laser Kleen" systems, the company generates between 60,000 and 80,000 gallons a day of wastewater, primarily from the raisin-washing process.Regulations concerning water run-off and the need to protect much needed local aquifers are strict and the Bedrosian family, long-time residents of the area and solid corporate citizens, wanted to do everything possible to provide for a sustainable business. This meant that standard solutions for disposing of the wastewater wouldn't suffice.

National Raisin's plant engineer, John Minazzoli, first considered spiral RO elements that are relatively inexpensive and require the least amount of floor space. However, dust and other grape solids (bits of stems and skins) were blocking the small channels in these spiral elements. Conventional pre-filters used upstream from the spiral elements also became blocked.

Once the full system was running and the concentrated sugar water (called "retentate") had been removed, the remaining water (called the "permeate") was actually lower in dissolved solids than the well water that feeds National Raisin's plant. Therefore, this water was available for re-use or could be sent to irrigate nearby vineyards.

National Raisin is continuing their program of optimizing RO use for maximum return on their investment. The original cost of the installation was recouped in less than two years. Demand for grape sugar water tends to fluctuate (even dropping to zero occasionally), but the savings on National Raisin's wastewater disposal bill alone amount to around $300,000 per year. The disposal saving by itself is enough to keep the system return-on-investment within the original plan of three years. Any additional income that comes from selling the concentrated sugar water to distilleries is an added bonus.

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