Thousands of gallons of water are used everyday at biodiesel production facilities like Renewable Energy Group's (REG) plant in Ralston, Iowa. The research facility experiments with the biodiesel process and has a production capacity of 12 MMgy. It shares its water supply with West Central Cooperative's Soy Center, which uses up to 43,000 bushels of soybeans per day to produce soybean meal.

Prior to the implementation of improvements to the water treatment system, the total water consumption between the facilities required 8,000 to 10,000 gallons of water each day. Facility managers looked at ways to conserve water and improve production quality.

"We want to be smart about water usage," says Randy Daniel, West Central's soy production manager. "It's environmentally and economically important to us. Lower water use conserves local resources while reducing our production costs."


Figure 1. REG's water usage dropped considerably after installing an RO unit.

Daniel and his team implemented an idea that has done just that. They began using a water treatment system that creates dramatic water savings. Daily usage (Figure 1) was reduced from an average of 9,000 gallons to only 3,000 gallons per day. This was achieved by installing a reverse osmosis (RO) system to treat the water prior to distribution to the plant facilities.


Figure 2. The previous water system, shown on the bottom, used three water softeners.

A Water System Improvement
The facilities' hard well water contains high levels of iron and other dissolved solids. The previous system had a high volume of water blown down through the boilers and cooling towers due to the inorganic materials remaining in the water (Figure 2). The well and water softener were located adjacent to each other. However, the softeners were located at remote locations throughout the facility near points of use. Maintenance of the three units in remote locations was not an ideal situation. In addition, the softeners were not producing the quality of water desired by REG and West Central. Consultants Thompson Environmental and Shive-Hattery Inc. were brought in to examine the facility. After discussing the issues with the consultants and evaluating their options, the managers decided to update with a RO process.

The decision to invest in RO was significant. The managers had to weigh short-term costs with long-term benefits. Costs for the RO system included equipment, start-up and support costs, installation and electrical/mechanical infrastructure, and design and construction phase costs. The total price tag was approximately $138,000.

Upon installation, the RO unit reduced levels of iron, alkalinity and other dissolved solids. Even when treated through a water softener, a high volume of water was "blown down" through the boilers and cooling towers due to the inorganic materials remaining in the water. The new RO system drastically improved the water quality, reduced water usage, allowed the elimination of the water softeners, reduced equipment repairs and improved operating efficiency. The investment began to pay off immediately.


Figure 3. The RO unit greatly improved water quality.

› Improved water quality REG and West Central took samples before and after installation of the system (Figure 3). The raw well water contained iron levels of 3.3 parts per million with a pH of 7.6 and alkalinity of 440. Post-installation water improved to .03 parts per million of iron, 5.7 pH and 4.9 alkalinity. As noted after the sample point in Figure 3, a caustic soda feed was included with the installation to increase the pH to approximately 7.0.
› Reduced water usage The "well run time" decreased with less demand for water. Production that once on average required 9,000 gallons per day went to just 3,000 gallons per day. There is less depletion of groundwater and the amount of wastewater has been significantly reduced.
› Eliminated water softeners and reduced equipment repairs The three water softeners were replaced with one RO unit, eliminating the need to continually purchase salt. It is anticipated that pump life will be extended due to the shorter run times. Since there are fewer solids in the water fed to the cooling towers and boilers, the cycle times are extended to reach their conductivity set points. The result is that these units are now using less water with more infrequent blow-down cycles.
› Improved operating efficiency "The RO unit has streamlined operations for us," Daniel says. "We've minimized waste with an easy-to-maintain water treatment system."

Even the "rejected" water from the RO unit is reused in a soybean wetting process at West Central's Soy Center.

The New Process, Lessons Learned
Before converting to the RO system, water softeners at each distribution point treated well water. This meant maintaining and feeding salt into three pieces of equipment. The RO system replaced the three stations with one water treatment station.

Figure 2 shows the process. Well water is pumped through an induced-draft aerator and into an iron filter. The next stop is a Siemens water technology Vantage M83-100 Reverse Osmosis Unit.

Shive-Hattery and Thompson Environmental recommended the Vantage M83-100 system because it was the right size for the facility. The compact footprint saves valuable floor space with "clean-in-place" connections that make serving it relatively easy. The only regular maintenance is periodically cleaning the membrane.

As water flows into the Vantage M83-100, contaminated water is put on one side of a membrane that acts as an extremely fine filter. Pressure is applied to stop and then reverse the osmotic process, resulting in much purer water. Rejection rates are low, approximately 25 percent.

A pH controller is tied to the caustic soda feed to adjust water pH levels. On average, readings show a 7 pH level. From here, the water is distributed to various areas: biodiesel, boiler feeds, cooling towers, lab feed and the soy center.

The new water treatment system is capable of flowing 100 gallons per minute with 75 percent of the water going on to be used in the biodiesel production and other needs. The reject water goes to the soybean wetting process.

On a typical day, the water demand is 60 to 80 gallons per minute. The system runs about 35 minutes every hour, 24 hours a day. The RO unit delivers highly purified water for the biodiesel process, very little water is wasted and plant managers are much happier with end results.

The key to a successful RO unit installation is talking with suppliers and equipment manufacturers to find out what product will provide the best performance. A qualified, experienced design consultant can help you find the right fit for your facility.

With the right RO system, your production efficiency will improve with water pure enough to feed all parts of your operations including cooling towers, boilers and your production line.

Michael Hall is a professional engineer with Shive-Hattery Inc. Reach him at mhall@shive-hattery.com.

The claims and statements made in this article belong exclusively to the author(s) and do not necessarily reflect the views of Biodiesel Magazine or its advertisers. All questions pertaining to this article should be directed to the author(s).