FOOD AND BEVERAGES
Almost all membrane technologies can be applied in a typical corn refinery: microfiltration for clarification and concentration of suspended matter, ultrafiltration for fractionation of starches and proteins, concentration and dewatering of starch suspensions or steepwater by reverse osmosis, and purification and fractionation of organic acid fermentation broths using nanofiltration and electrodialysis.
Steepwater is a dilute suspension of amino acids, peptides, protein, sugars and minerals leached out from the corn during soaking. It has a density of about 4°Be and an osmotic pressure of about 150 psi (10 bars). It is concentrated today by evaporation to about 50 percent solids. For a capacity of one million liters per day (180 GPM) of steepwater, a mechanical vapor recompression (MVR) evaporator would require energy inputs of 1300 kW of electrical power and 3300 kg/hour of steam. In contrast, if RO was used ahead of the MVR to remove 57 percent of the water, the energy requirements would reduce to 360 kW and 1300 kg/hour of steam for a potential savings of about $580,000 per year.
For the production of sweeteners, a typical dextrose stream from the saccharification reactor is 95 DE (dextrose equivalent), 30-35 percent total solids, containing about 0.2 percent suspended matter (termed "mud" in the industry). This application is perhaps the most developed, since it can save a substantial amount of money in purchasing and disposal of the filter aid (usually diatomaceous earth). In general, spiral-wound MF membranes of 0.1 micron pore size are used, although there are some applications where a tighter membrane may be preferred. For a system operating with a 90 percent yield of clarified dextrose at 70,000 liters per hour (3000 GPM), the capital cost of the membrane plant would be about $500,000-700,000 and save at least $3200,000 per year in filter aid costs alone.
Osmonics is a major supplier of RO systems to remove enzymes and other impurities from corn derived sugar syrups. The company also sells systems to reclaim sugar waste.
When a large East Coast sugar company had problems disposing of sugar wastewater, they turned to Osmonics. The sugar company uses insulated stainless steel-lined tanker trucks to transport sugar and corn syrup to their customers. To combat microbiological growth, each truck is cleaned and sanitized with a hot water rinse after delivery. Rinse from the truck wash contains 1.5 to 5 percent sugar, exceeding the BOD disposal limits by thousands of mg/L and posing a significant waste disposal problem.
After performing an application test and a large batch pilot run on the truck rinse water, Osmonics engineers determined that reverse osmosis could concentrate the rinse into a 25 percent sugar solution and provide a rinse stream that meets discharge limits. A sugar solution this concentrated could be sold for animal feed, turning what had been a disposal problem into an extra source of income for the sugar company.
Osmonics incorporated a high temperature, high pressure RO system into the sugar company's operation. This system is able to process up to 12 gallons per minute (2.7 m3/h) of the rinse water, producing a concentrated sugar solution for resale and recycling purified water to the truck wash. By purifying the water while it is still hot, the recycled rinse water requires minimal reheating. The end result is lower operating costs for the sugar company and a creative additional source of revenue.