Water Use and Wastewater Loading in the Food Processing Industry
Intern Project Summary, Minnesota Technical Assistance Program, University of Minnesota
Intern Project Date: Summer 1996
Intern: Jeremy Yarwood, University of Minnesota, Civil/Environmental Engineering Senior
Company: Sparta Foods, St. Paul, Minnesota
Results: Reduced water use by nearly 1.9 million gallons a year.
Sparta Foods is a Mexican food producer manufacturing flour tortillas, salsa, barbecue sauces, corn tortillas and corn chips. They have approximately 125 employees.
Before the intern project, Sparta used an average of 25,000 gallons of water daily, costing $125 a day in sewer fees. In the past, they had paid as much as $25,000 annually in strength charges for total suspended solids (TSS) and chemical oxygen demand (COD).
The wastewater treatment plant was going to access service availability charges (SAC) of $10,200 unless Sparta was able to show reduced water use.
Processing whole-kernel corn accounts for 70 percent of Sparta's overall water use. Water is used to cook, transport and wash the corn.
Corn Flushing. After being cooked, the corn was flushed with water to cool it and lower the pH. The intern found that the flushing was ineffective at cooling corn below the surface and the pH was relatively unchanged regardless of the time for flushing.
Automatic shut-off valves were installed to control the amount of water used to flush the corn. The valves will help eliminate excess flushing and reduce tank overflow by decreasing the volume of incoming water.
Savings: Approximately $4,500 in water costs annually by eliminating the use of 3,000 gallons of water daily10 percent of overall water use.
Corn Transporting. Sparta used 5,200 gallons of water daily to transport the corn from the cooking tanks. The intern researched dry methods to transport corn: 1) Screw conveyors were unacceptable because they degraded the corn. 2) Although belt conveyors might work on the vertical cook tanks of the chip line and reduce water by 10 percent, the initial investment was not justifiable.
In a test, the intern recycled 20 percent of the transport water back into the process. Recycling did not affect product quality, neither pH (which affects shelf life of the product) nor cleanliness (which affects appearance). Higher recycling rates could be tested to determine what rate is most efficient for the process while maintaining product standards.
Potential savings: Recycling 20 percent of the transport water could save approximately 1,040 gallons daily3.5 percent of overall water use savings $1,570 annually.
Equipment Cleaning. The flour product line is first given a dry cleaning by scraping and blowing compressed air over the equipment. After a sweeping, high-pressure washers and normal garden hoses are used.
High-pressure washers ($200) can replace the garden hoses to clean the equipment more quickly and efficiently, using half the water.
Potential savings: Replacing hoses with high-pressure washers will return a savings of $1,050 per year by reducing water use by 217,000 gallons annually.
Substituting Ingredients. Using corn flour eliminates the need for water to cook, wash and transport the whole corn. Sparta plans to substitute corn flour in only ten percent of its stone-ground corn products because switching from stone-ground corn to flour can alter product quality.
Potential savings: $2,300 per year from reducing water use by 477,000 gallons annually. Decreases water use by five to six percent.
Lawn Sprinkler. Sparta has already reduced water use by shutting off the lawn sprinkler system. During August, the system used 84,000 gallons, 8.4 percent of the total water used.
Savings: Over $400 a month in water costs.
Because the corn wash water elevates TSS and COD levels in the wastewater, the intern investigated several options for removing the corn solids for use as animal feed. An estimated one ton per day of corn sludge could be reclaimed if solids could be removed.
Because the sludge has a 95 percent moisture content the food recycler's pick-up fee would not be economical. Reducing the moisture to 60 to 70 percent by dewatering would eliminate any pick-up charges.
Options. Several equipment options were identified: 1) A filter followed by a centrifuge was too expensive. 2) With the gravity screen and belt press, the press was unable to remove water when tested. And, 3) a rotating drum with an evaporator was not tested.
Potential savings: If a workable method is found, Sparta could save $16,500 in strength charges per year.
Implementing water conservation options has reduced Sparta's water use by nearly 1.9 million gallons a yearsaving almost $10,000 annually. They are working toward reducing water use by 25 percent overall.
MnTAP has a variety of technical assistance services available to help Minnesota companies to manage and reduce their industrial waste. If you would like assistance or more information about MnTAP's Intern Program, call 612/627-4646 or 800/247-0015 from greater Minnesota.