Given its prevalence, filtration is becoming a core technology in food production. It purifies process water, cleans waste streams, even sterilizes compressor air. It is part of the revolution in nanotechnology, which is paving the way into processes formerly reserved for evaporation and other technologies. The particular requirements of the food industry are being addressed with numerous advances in sanitary design and reduction in biochemical oxygen demand (BOD) and chemical oxygen demand (COD) from waste streams.
Sanitary considerations dictate bypass flow around the outside of a spiral-wound filter to prevent dead zones and allow the filter to be flushed during CIP cycles. As much as 60% of the feed stream may bypass the membrane, and recirculation costs escalate along with the price of electricity. Assuming $0.10 per kwH electrical cost and a 30% bypass rate, a 30 hp recirculation pump adds about $8,000 to annual operating costs, estimates Peter H. Knappe, president of TriSep Corp., Goleta, CA.
Most sanitary membrane elements use a net wrap to control bypass flow and maintain mechanical stability, Knappe says, but a tight tolerance with the element’s outer diameter is difficult to hold. As the element’s diameter increases, pressure differential also increases, resulting in destructive force that shortens the element’s useful life. “The higher the solids content, the bigger the problems that occur,” he says. Net wrap usually is composed of a polypropylene sheet and epoxy resin. Epoxy failure is the most common replacement cause for spiral wounds, not the membranes themselves, notes Jose Carpio, a membrane specialist with Alfa Laval in Richmond, VA.
Rather than a net or cage wrap, Knappe and his colleagues at TriSep devised an impermeable, hard plastic shell with a groove to spiral the bypass flow from one end of the element to the other. The turbulence created helps prevent fouling with minimal flow-through. “We’re sizing it so there’s about 0.06-in. tolerance,” he says. TriSep fabricates both membranes and cartridges, though the shell can be fitted with other manufacturers’ membranes.
Thanks to their huge surface areas in a compact space and relatively low cost, spiral-wound membranes are industry workhorses. They are breathing new life into old technology, helping to concentrate fluid streams to make downstream dryers and plate-and-frame filters more cost-effective. Alfa Laval has supplied plate-and-frame units for more than half a century, and the acquisition of spiral-wound fabricator Danish Separation Systems has kept the older units viable in a time of rising energy prices. Alfa Laval installed a new spiral membrane in lieu of a dryer at Danish Crown’s Edidan facility to concentrate porcine blood plasma to 8.5% solids before it went to a plate-and-frame, which can handle high viscosities. Capacity went up, while energy consumption plummeted.
Advanced membrane separation (AMS) is a term coined by GE Water & Process Technologies for an alternative process to evaporation in fishmeal production. AMS coalesced six years ago in discussions with Bodø Sildjefabrikk, a Norwegian processor. The plant works with fish stick water composed of viscera and high in salt and biogenic amines, signals of spoilage. Evaporation didn’t remove the salt and amines, resulting in meal that fetched a low price, recalls Mark D. Rottman, GE’s global initiatives leader-advanced separation programs. Operating the evaporator when oil sold for $30 a barrel cost $612,000 a year. At $70 a barrel, electrical cost spiked to $1.5 million, a level that threatened to put the 98-year-old processor out of business. Two-stage filtration dropped energy costs to $110,000; even with cleaning chemicals and membrane replacements, operating costs were a fraction of evaporation. Because 80% of salt and most amines are filtered out, the finished product commands a higher price. Foul odors that offended neighbors no longer are produced.
But special materials were needed to prevent the tacky stick water from clogging the membranes after two hours, and considerable trial and error was involved in process engineering. Two-stage filtration of stick water was a departure from earlier approaches, says Rottman, and different equipment arrays were tried over a two-year period. The payback goes well beyond Bodø Sildjefabrikk and other fishmeal plants worldwide, however. “Because the process improves the quality, the addition of a sanitary membrane could produce powdered fish protein fit for human consumption,” he says. AMS could do for fishmeal what ultrafiltration has done for whey processing in cheese plants.
The BOD SquadWastewater pretreatment is an issue in all industries, but high levels of suspended and dissolved sugars, protein and fat pose a special challenge for food plants. Water quality measures of BOD and COD are prompting some plants to install membrane bioreactors (MBRs) and other filtration technologies once considered too exotic.
“The food industry has some of the highest concentrations in industry of biodegradable particles,” observes Dave Garrett, a wastewater engineer with Kansas City, MO-based Burns & McDonnell engineering. “Whether it’s corporate responsibility or a goal to re-use effluent for cooling towers and boiler feed water, companies are a lot more interested in MBR.”
The cost and availability of fresh water is becoming an issue for some facilities, and many regulators are mandating organic load reductions. Dissolved air filtration in which pressurized air is injected into a waste stream to create micro air bubbles is used in meat and poultry to remove fat from wastewater, and the technique is beginning to find its way into other industry segments. Typically, oil adheres to the bubbles and is skimmed away before the waste undergoes additional processing. Garrett cites a specialty ingredient manufacturer who recently incorporated dissolved air filtration to capture particles that are sold as animal feed.
Fibrous balls that can be compressed or relaxed to remove phosphates and other suspended solids as small as 4 microns is a filtration technology making inroads in the poultry sector. An alternative to sand and disk filters, the so-called “fuzzy filter” has been sized to handle as much as 2,000 gallons of effluent a minute, according to Bill Kunzman, a vice president at Trussville, AL-based Schreiber LLC. Besides handling significantly higher volumes in a smaller footprint than other filters, compression rates can be varied to respond to system upsets when flow-through increases.
Declining prices for MBR are encouraging more food plants to incorporate hollow-fiber filtration in wastewater treatment, notes Paul Greene, global director for food and beverage applications at Warrendale, PA-based Siemens Water Technologies. “MBR can double or triple throughput capacity,” an important efficiency for plants contemplating an expansion. For facilities without space for an expanded aerobic treatment system, MBR may be a necessity. The growth in MBR applications prompted Pall Corp. to develop its own MBR filters, which will be introduced to the market soon.
Solids loads of 2% are attainable with today’s MBRs, a level that would have been out of the question in years past, says Greene. Air scrubbers to prevent fouling mean less maintenance is required. “We’re working smarter and no longer renting cranes” to pull units out of tanks, he says. “Once-a-month cleaning is our target.”
US Filter, which was acquired by Siemens three years ago, installed a wastewater treatment system eight years ago at Rahr Malting Co., Shakopee, MN. The state-of-the-art system discharged BOD at 12 mg/l into the Minnesota River. A similar system augmented with MBR is being installed for another malt producer, and effluent BOD will be less than 5 mg/l, Greene says. “There’s no smell, no color. It’s water white.”
Economies of scale“The cost of membrane filtration continues to come down as the number of systems online go up,” reflects Bruce Blanchard, a sales manager with GEA Filtration in Hudson, WI. Higher throughput also encourages the technology’s deployment. “A cheese plant processing 1 million pounds of milk a day used to be a big deal,” he says. “Now, 5 million pounds is entry level.”
GEA continues to refine a ceramic cross-flow microfiltration system that recovers dairy fat from mozzarella cookers. The system eases pollution abatement pressures, and the recovered solids provide a payback. Milk fat prices have climbed to $2 a pound, Blanchard says.
Ultrafiltration of process water with hollow fiber membranes that can be backwashed is becoming more common in dairies and beverage facilities. Food safety, product consistency and maintenance savings are motivating food plants to make the conversion from sand filters, diatomaceous earth and disposable filters, according to Steve Howell, a vice president with Port Washington, NY-based Pall Corp.
Pall fabricates a UF system called Aria, a PVDF membrane that can tolerate chlorine and ozone. It filters bacteria, protozoa, some viruses and organic molecules as small as 5 microns. The system often is used to prefilter process water prior to reverse osmosis. It also is applied at an unnamed yogurt plant concerned with microbial contamination in municipal water. Disposable filters could meet quality standards, but the UF system offered two additional benefits: standardized validation testing and a useful life of three-plus years. “The life on hollow fiber is years longer than spiral-wound membranes,” Howell says, “and you can integrity test the system on a daily basis to show there were no breaches.”
The yogurt installation involved two UF membranes to meet a specification of less than 100 CFU/ml total plate counts on process water. It handles 10 million gallons of water a year and peak flows of 9,600 gallons per hour. The system cut filtering costs in half at the high-volume facility, compared to disposable filters.
Chlorine destroys R/O membranes. Beverage plants using R/O filtration routinely filter out the chlorine in municipal water, then add it back after R/O when the water is stored. While pumping the ingredient water to the process area, chlorine is removed again. It’s a great process for chemical suppliers, not so good from a water utilization perspective. With water conservation becoming a priority, companies are rethinking the process and, in some cases, returning to chlorine-tolerant nanofiltration, according to Mike Lowry, senior sales engineer-beverage systems with GE Water & Process Technologies.
Nanofiltration is the technology of choice at Gatorade’s Blue Ridge plant (“Sustainability with Attitude,” Food Engineering, October 2007). Today’s R/O systems are more efficient, Lowry reports, with only 20% of incoming water failing to make it through the filters, down from a 25-30% rejection rate in years past. Nanofiltration, on the other hand, only rejects 10% of incoming water. “Some nanofilters are approaching the mid-90s in water utilization, and in the next 5-10 years, the high-90s should be attainable,” he predicts. At Gatorade, the savings over R/O amount to more than 40 million gallons of water a year, Lowry adds.
Security concerns dovetail with food safety at major food companies adopting new protocols for compressed air filtration. Malicious placement of a biological contaminant at the inlet of an air compressor could contaminate an entire plant. As a precaution, some manufacturers are shifting to high-efficiency coalescing filters.
“Compressed air is a preferred utility, particularly in cold and humid environments where electrical equipment is prone to deterioration,” observes Allan Fish, a senior filtration manager with Parker Hannifin Corp., Haverhill, MA. Unfortunately, air pipes are ideal media for bacteria: As they snake from warm to cold spots, condensation occurs. Moist, hot air is nirvana for microbes, and with compressed air being used to blow open pouches at fillers and being vented to the process area, the potential for disaster exists. Inert Teflon fiber filters are being used to clean compressed air after sintered bronze or plastic filters have removed oil and condensate. Three-stage filtration will deliver sterile air, removing anything down to 10 nanometers (0.01 microns).
That level of filtration was reserved for aseptic processes in years past. Today, cost is down, and reliability is up, encouraging food engineers to deploy the technology more widely. The same is true for most types of filtration. Coupled with the potential to improve throughput or recover desirable elements, filtration is assuming a larger role in food manufacturing. u
For more information:
Jose Carpio, Alfa Laval, 804-545-8307
Dave Garrett, Burns & McDonald, 816-333-9400
Ramesh Gunawardena, FMC FoodTech Inc., 419-626-0304,firstname.lastname@example.org
Mark Rottman, GE Water & Process Technologies, 513-300-0007,email@example.com
Bruce Blanchard, GEA Filtration, 715-377-0533,firstname.lastname@example.org
Steve Howell, Pall Corp., 516-924-2053,email@example.com
Allan Fish, Parker Hannifin Corp., 800-343-0051,firstname.lastname@example.org
Bill Kunzman, Schreiber LLC, 205-655-7466,email@example.com
Paul Greene, Siemens Water Technologies, 518-758-2179,firstname.lastname@example.org
Peter Knappe, TriSep Corp., 805-964-8003,email@example.com
Trans-free foods make case for centrifugal filtrationMarket trends and food safety concerns can change the payback equation for processing equipment, as the movement to centrifugal filtration of cooking oil illustrates.
Partially hydrogenated oils produce closely packed molecular structures in fryer-oil fines, and a mesh filter suffices in removing them. The same isn’t true of the sediment in oils formulated without trans fat. To extend the use of these more expensive oils, centrifugal separation is a must.
“We saw this trend coming,” says Ramesh Gunawardena, manager-technology & process development for FMC FoodTech Inc., Sandusky, OH. Because much smaller particles are removed than with mesh systems, centrifugal filters also are effective in controlling allergens, a concern when multiple products pass through a fryer. In the case of wheat gluten, complete allergen removal was demonstrated in lab tests. Different binding characteristics and operating temperatures are factors in how much is removed, Gunawardena points out.
FMC FoodTech worked with Cincinnati-based Tema Systems to modify a bowl-and-scroll centrifuge designed for petrochemicals and adapt it to food production requirements. “The sophistication of the design is what distinguishes this precision unit,” says Gunawardena. “Tight tolerances and backflushing capabilities are part of the design. Based on field studies, we built in the capability to inspect the unit after CIP.”
The scroll spins at slightly higher speed than the bowl, rotating at 2,400-3,000 rpms. Filtered oil discharges from the back of the bowl, while sediment moves toward the conical end for discharge into a bin. Independent lab analysis found that 25-50% less oil remains in the fines than with mesh filters.
Quantifying filtration of minute particles is difficult. As a rule, the centrifuge removes all sediment larger than 5 microns and 98% of particles down to 1 micron. The comparable numbers for multi-stage mesh filters are 50 and 25 microns.