Course: BFM 101 Biofuels Fundamentals

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Reducing Consumptive Water Use

The major processes using water in ethanol facilities are: 1) biochemical processes for converting corn to ethanol; 2) reverse osmosis for water treatment; and 3) cooling. Many technologies are used to recycle and reuse water in the facilities to reduce the discharge or consumptive use of water.

The concept of Zero Liquid Discharge (ZLD) is part of the water recycle and reuse effort in the ethanol industry. Some recently constructed facilities have adopted ZLD to meet regulations, for example, in the Central Valley of California. ZLD must maintain high quality water compatible with biological processes. Most water demand is from cooling towers and boiler systems.

Steps in ZLD include: 1) management changes, such as cold lime softening, recycle loops, and generating CO2 in the facility rather than importing it; 2) diverting cooling tower water and reverse osmosis concentrate to the supply water tank, 3) and treating the supply water tank as a blend tank. With ZLD only a small fraction of steam escapes the system.

Industry Reports Success with Zero Liquid Discharge

Ethanol Producer Magazine reports industry experts who indicate that zero liquid discharge can result in a 20 to 30 percent decrease in water needs.  However, each facility requires a unique design.  U.S. Water Services, who provide retrofits to water systems, has four approaches: recycling water using cold lime softening, evaporation or crystallization of the discharge stream, and evaporation ponds, which only work in the Southwest.  One retrofit described by Mike Mowbray, marketing manager for U.S. Water Services, “reduced water usage from about 3.5 gallons per gallon of ethanol, to 2.8 gallons with the addition of cold lime softening. Further conversion to zero liquid discharge decreased water use at the plant to just over 2 gallons of water per gallon of ethanol [7].

Facility Co-location and Water Reuse

Locating ethanol production facilities near other industrial operations that use water is a way to reduce impacts on local aquifers and water supplies. The discharge water from one industrial facility can be reused by another, therefore reducing its draw on ground water or surface water—making the two facilities more efficient water users.

Examples of this practice include two co-locations described by POET. POET is the nation’s leading ethanol processor. POET operates a network of 27 plants in seven states in the North Central Region, and produces more than 1.6 billion gallons of ethanol annually. Their Portland, Indiana, facility produces 68 million gallons of ethanol annually, and is co-located with Meshberger Berger Brothers Stone Corporation (Quarry) to share water resources. Because the City of Portland could not supply the water needed by POET, they now receive the water released by the quarry, and 100 percent of their manufacturing water used is this water. Only potable water needs are met from wells [8].

Another example is POET’s Caro, Michigan facility. This facility produces 53 million gallons of ethanol annually, and is located next to the Big Stone Power plant. The power plant’s cooling pond is refilled each spring by snowmelt into Big Stone Lake. The holding pond provides 100 percent of the processing water for the ethanol facility. All of the wastewater generated by the ethanol plant is recycled back to the cooling pond. Furthermore, 70 percent of the steam needs in the ethanol facility are provided by excess steam generated by the power plant [8].

These two examples indicate the benefits of co-location and water reuse. Future developments such as these collaborations, as well as improved water efficiency and Zero Liquid Discharge, will significantly reduce the water needed and consumptive water use by ethanol facilities.

Resources by eXtension, Bioenergy & Sustainability, BIOEN3 CC BY-NC-SA 2.5
www.extension.org/pages/63365/bioenergy-curriculum

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