Resource: WaterWorld
Thanks to an innovative process water reuse system and alternative energy, PepsiCo Frito-Lay's Casa Grande facility in Arizona is the first US food processing plant that produces drinking quality process water to be reused in food production. Here's how.
It is not unknown that food and beverage production is one of the most water intensive industries globally. Research from J.P. Morgan suggests that direct water use from five global food and beverage giants, including Kraft Foods and the Unilever Group, is enough to serve the daily basic water needs of everyone one the planet.

Driven by heightened regulation and sought after cost savings, these very food and drink companies are now integrating advanced water treatment technologies into their operations.

Earlier this year PepsiCo scooped the Stockholm Industry Water Award for conserving nearly 16 million cubic meters of water in 2011, from a 2006 baseline.

The company's Casa Grande, Arizona, Frito-Lay facility was cited for using a filtration and purification system that recycles and reuses approximately 80% of process water used in production.

CDM Smith completed the design and construction of the 2460 m3/day process water recovery treatment system, which recycles up to 75% of the facility's process water. As a result, Frito-Lay has been able to reduce its annual water use by 378,541 m3.
A unique design for bioreactors in concentric tanks, and the use of a GE Zenon MBR, activated carbon, LPRO and UV/chlorine disinfection help the treated effluent meet EPA standards
The advanced purification system incorporates screening, sedimentation, membrane bioreactor, activated carbon, ultraviolet, low pressure reverse osmosis, water stabilization and chlorine disinfection to treat the effluent to U.S. Environmental Protection Agency (EPA) primary and secondary drinking water quality standards, allowing it to be reused to wash and move potatoes and corn. This is the first U.S. food processing plant that produces drinking water quality process water to be reused in food production.

Several processes at the facility are large consumers of water. Potatoes are moved and washed in a flume as they are prepared for processing. During peeling and slicing, starch is flushed away. For corn, water is used in a caustic soak that loosens the hulls, also in a starch reduction step and in cooking.

Starch water is sent into a segregated water line so the starch can be removed and processed. The water and starch are separated in a vortex, high speed separation process. The concentrated starch is dewatered on a vacuum filter, and then it is dried with a hot air dryer, bagged and sold for use as commercial starch product.
Biological nutrient removal and ultrafiltration is used in the MBR process before the LPRO system to provide positive removal of solids from the bioreactor and solids too small for the screens and primary clarifiers to capture
Equipment cleaning and sanitation also consume water. Equipment must be cleaned before any flavor change and a more extensive cleaning is done every weekend. All process water goes into the recycle stream and on to the Process Water Recovery Treatment Plant (PWRTP). Sanitary water from restrooms and the cafeteria kitchen go to the city sewer.

At the PWRTP, a pump station lifts the process water up to internal fed rotary screens that capture corn kernels and pieces of potatoes and any large material. Water flows out of screens to an equalization tank, where staff adjust pH. From there it goes to primary clarifiers. Fine particles of corn and potatoes that settle in the primary clarifiers are removed by a bottom scraper. The settled material is blended with the larger screenings and then dewatered on a centrifuge. The dewater solids are used for animal feed.

After the primary clarifiers, water flows to into bioreactor tanks, where an activated sludge step provides biological nutrient (nitrogen) removal, followed by a membrane bioreactor featuring ultrafiltration with GE Zenon membranes. A pressurized granular activated carbon system helps remove color and reduces BOD and COD. Water is disinfected in a ENAQUA UV system prior to flowing into a Low Pressure Reverse Osmosis (LPRO) system. The LPRO features use of Dow membranes but was assembled by ENAQUA. There are three membrane arrays, with two being used for average flows seen at the plant.

Influent BOD is around 3500 mg/l and non detect on discharge. TSS is about 4,000 mg/l coming in and non-detect on the discharge. "We are putting out drinking water quality water," said Al Goodman, P.E., Principal CDM Smith. "In fact, it's better than drinking water."
The LPRO system provides final salts and dissolved organics removal. The system has redundant capacity with three trains available to the operators, including one fully redundant train for standby availability.
After treatment through the RO system, staff add sodium bisulfite to stabilize the water and sodium hypochlorite to provide a chlorine residual. It then flows to a 210,000 gallon reclaimed water tank.

The LPRO recovers 75% of the water, while the 25% reject water goes to the city sewer. City makeup water is piped into the reclaimed water tank and blended with the recycled water. Water from the reclaimed tank is eventually pumped back to the head of the plant to meet production requirements.

The Process Water Recovery Treatment Plant started up in May 2010 and has performed as expected, meeting all water quality testing requirements. The Casa Grande facility was the first snack food manufacturing facility in the United States to be awarded LEED Existing Building Gold Certification from the U.S. Green Building Council, thanks to educational elements, enhanced process layout and energy-efficient motors.

With 80% of construction debris recycled for beneficial reuse, dewatered potato peelings and corn kernels sent to local farms for feedstock, and recovered potato starch sold for other manufacturing uses, the facility now sends less than 1% of its overall waste to landfill.

The facility has a 5-megawatt photovoltaic solar system that produces almost all of the plant's daytime electricity needs. CDM Smith completed the entire photovoltaic solar installation, including 36 acres of photovoltaic panels on dual-axis ground-mount systems, single-axis concentrated photovoltaic collectors, and dish collectors with Stirling engine generators.

Goodman said the Casa Grande facility demonstrates that the technology exists to recycle water to the highest standards.

"We are quoting and proposing on other systems and other food and beverage companies that have seen this system," Goodman said. "We definitely see this as the path of the future."

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