Engineering R&D: Advances in Ozonation
As reported earlier by Food Engineering (September, '97), ozone -- a powerful oxidant which destroys microbes -- was affirmed as GRAS (Generally Recognized As Safe) by an FDA-recognized expert panel. According to the Electric Power Research Institute (EPRI) in Palo Alto, CA, ozone reacts up to 3,000 times faster than chlorine with organic materials and destroys both bacteria and viruses. Although the FDA has not yet listed ozone as GRAS, ozone is already finding applications in retarding spoilage and extending the shelf life of fruits, in cleaning and sanitizing food plants, and in disinfecting poultry process waters for reuse.
USDA's Food Safety & Inspection Service (FSIS) allows the use of ozone to disinfect poultry process water for reuse on a case-by-case basis. "Individual companies can come to the agency with experimental protocols for how they would want to use a particular technology in individual facilities on an experimental basis, until we actually get the regulations changed," said Dr. Daniel Englejohn, FSIS director of regulations development and analysis.
Poultry applicationsIn 1997 BOC Gases (Murray Hill, NJ) introduced the Macron Loop, which applies ozone to disinfect and recycle poultry chill water (FE September, '97, April '98). In the Loop, chiller water is pumped through mechanical filters which remove fats, oils and particles as small as 25 microns (half the diameter of a human hair). Filtration reduces the organic load which feeds microbes, reducing the amount of ozone needed for disinfection. The filtered water is then injected with ozone gas, created on-site by a generator which feeds oxygen through an electrical "corona discharge" field, and pumped into the chiller bath.
Early this year, BOC partnered with Ecolab, Inc. (St. Paul, MN) to integrate the Macron Loop with Ecolab antimicrobial agents for poultry-chill baths (FE March, '99). Ozone dissipates rapidly, so agents such as Ecolab's Oxxium chlorine dioxide (generated on-site) or Tsunami peroxyacetic acid-based solutions are added to maintain antimicrobial treatment in the water. Ozone disinfects the water, while the other agents disinfect carcasses in the water. Tsunami, now applied in fruit and vegetable wash-water and flume systems, rapidly degrades into water, oxygen and acetic acid after use. Chlorine diox-ide degrades in-to oxygen and acetic acid.
FSIS' "zero tolerance" of visual fecal contamination on poultry carcasses entering the chiller bath has substantially increased the use of water in poultry plants. Carcasses are continuously washed and sprayed all along the process line -- from scalder through evisceration, through inside/outside bird washers (IOBWs), through inspection stations and rinse cabinets -- before entering the chiller bath. FSIS also requires 1/2-gallon chiller makeup water per carcass for broilers, 1 gallon for turkeys, unless the plant receives specific approval to reduce or eliminate that requirement.
BOC first partnered with the ConAgra Poultry Co. plant in Gainesville, GA, to develop the Macron Loop for recycling and reclaiming chiller water. According to Plant Manager Willie Lee, the plant is working toward the half-gallon per bird reduction in chiller makeup water, and "the loop system has a lot of potential for water reclamation other than chill water. We're now looking at either incorporating water from inside/outside bird washers and rinse-cabinets into the loop, or reclaiming it through a separate system. We should show some significant water savings by doing that."
Zentox Corp. and Praxair are introducing the Cascade Poultry Water Reuse System, designed specifically for poultry kill plants. The system utilizes ozone to kill microorganisms in used water from collection points such as inside/outside bird washers and rinse cabinets, then returns the water to other reuse points. Developed by Zentox, a water-treatment company, in partnership with Praxair, the system is available in several sizes ranging from 200 gpm to 1,000 gpm and can be installed outside the processor's building. Zentox furnishes turnkey installation, engineering and on-site management; Praxair supplies the ozone generators and bulk oxygen.
Water is typically taken from IOBWs, final rinse cabinets and high-pressure spray systems "which are typically discharging pretty clean water," says Moore. Depending on plant design, water might also be taken from other sources such as the inspection line, neck and giblet harvesters, and chill baths.
"We try to return the water to where we won't create a closed loop; this helps to avoid a mineral buildup," Moore continues. Good places to direct return water include the evisceration line, chiller makeup and the scalder. "The key is to identify continuous users of water in the plant, and balance the system out," he adds.
Fruit applicationsTastee Apple, a producer of caramel-coated apples, apple juice and apple chips located in Newcomerstown, OH, extends product shelf life, conserves water and reduces wastewater BOD loads with ozonation systems supplied by Novazone (Livermore, CA).
The first system was installed mid-1998 to replace chlorine in flume water, which floats field or storage apples from 950-lb. bins toward a conveyor for further processing. EPRI and local utility American Electric Power shared the $50,000 equipment cost of the ozone system with Tastee Apple, and helped evaluate system effectiveness. The 2,000-gallon flume circulates water at about 600 gpm and handles about 40,000 apples per hour. Flume water collects high levels of soil and organics from the apples, and formerly had to be dumped daily.
To ozonate the water, a side stream of about 60 gpm is first filtered through an 80-micron filter with intermittent backwash capability. Gaseous ozone, generated in a 5-lb. per day corona discharge unit supplied with dried air, is then injected into the side stream to maintain ozone in the flume water at 0.05 to 0.15 ppm. An ozone-detection unit continuously monitors the flume area to ensure that ozone in the air does not exceed the OSHA limit of 0.08 to 0.1 ppm.
Results: Flume water can now be reused for an entire week instead of daily replacement, saving more than 12,000 gallons of water per week. Because the system runs 24 hours per day -- even at night when no apples are washed -- it reduces flume water BOD to less than 50 mg/l.
Novazone operates a Mobilzone 6 x 8-ft. walk-in trailer for field-testing ozone as a sanitizing agent for food products or process equipment, and to extend the shelf life of fruits by oxidizing the ethylene they generate and destroying mold in storage rooms and containers. According to Novazone President Lee C. Ditzler, two factors are driving ozone as a replacement for chlorine: the elimination of dangerous byproducts; and the growing immunity of microbes to chlorine, requiring processors to use ever-higher levels of chlorine. "Ozone kills by oxidizing; you don't build immunity to that," he observes.
DEL Industries (San Luis Obispo, CA) recently introduced a portable spray-wash system which applies ozone-enriched cold water rather than hot chlorinated water or other harsh chemicals for sanitizing surfaces in food plants. The unit operates at low pressure (about 32 psi) and conserves energy by using cold water. According to Dr. Brian Hanson, professor of food science at California State Polytechnic University who is evaluating the system, "we're seeing 50 to 100 percent reduction in total plate counts on various surfaces," using both standard laboratory tests and ATP bioluminesence tests.