Balancing the Energy-Water Nexus

By Nathan Schock

Energy and water. Water and energy. Both are critical to human development, and both are strongly interrelated.

With few exceptions, water is necessary to generate and distribute energy. In turn, water can’t be collected, purified and transported without energy. A term has even been coined to describe the relationship: the Energy-Water Nexus.

For a company like ours, operating a network of 27 biorefineries with the capacity to annually produce 1.6 billion gallons of ethanol, strategic thinking about water is a necessity. We spend a lot of time thinking about how we use water and where it comes from. More specifically, we focus on conserving water by using less and drawing it from alternative sources.

An ethanol biorefinery needs water primarily for three things: to create the aqueous environment necessary for fermentation, to generate steam in the boilers and to subsequently cool the process systems by removing heat. The perception exists that it takes a lot of water to make ethanol, and at one time that was true. In 1988, our first year of operation, our biorefinery required 18 gallons of water for every gallon of ethanol produced.

But at that time, the industry was in its infancy, technology was unreliable and virtually no ethanol plants were operating profitably. Significant gains had been made by 2009; so that same gallon of ethanol produced in one of our facilities required just over three gallons of water.

How did we do it? How were we able to decrease our water use by more than 80 percent? It was through a sustained focus on both the efficiency of the entire ethanol production process and the specific issues related to water use.

Efficiency improvements in the overall process have contributed significantly to the decrease in water use. In many cases, sustainability can involve trade-offs. But in the case of the Energy-Water Nexus, a decrease in energy use often leads to a corresponding decrease in water use and vice versa.

In our case, the development of a “no-cook” fermentation process decreased our energy use by 10-15 percent and meant that less water was needed to cool the biorefinery. But that’s just one of many examples. When you add them all up, we’ve cut the energy it takes to produce a gallon of ethanol approximately in half since 1988, which has led to cuts in the amount of water needed for cooling by a roughly equivalent percentage.

Gains have also come from focusing specifically on water. Water use is benchmarked across our biorefineries and receives as much attention as production rates. All of the water used in the fermentation process is recycled and we have been able to significantly reduce water use through process optimizations and technology improvements.

In addition to decreasing the volume of water used, our biorefineries also seek out alternative sources of water. For example, nearly all of the water to operate one biorefinery comes from the retention ponds of a nearby power plant. Another draws all of its water from an adjacent quarry that discharges it as part of its normal dewatering process. Yet another gets a third of its water from a local wastewater treatment facility. Last year, one of our biorefineries was able to save almost 16 million gallons when it started using water collected onsite in stormwater retention ponds.

Our belief in the importance of water conservation led us to make further reductions in water use through the first goal of our sustainability initiative, Ingreenuity, which we launched in 2009. That goal is to decrease overall water use by a further 23 percent from 2009 levels by 2014 so that our facilities would average less than 2.5 gallons of water per gallon of ethanol produced.

The goal was ambitious, but our engineers have us on the right track. They came up with a patent-pending process called “Total Water Recovery” that recycles water streams that were previously discharged. That process has now been installed in 18 of our biorefineries and plans are in place to deploy it in all but two of the remaining nine.

Thanks to Total Water Recovery, we used approximately 2.76 gallons of water per gallon of ethanol produced last year and in 2012 we project that it will decrease to 2.61. That would represent a water savings of 805 million gallons from where we were in 2009. If we achieve our full goal, that would save about one billion gallons of water each and every year.

The Energy-Water Nexus is a real phenomenon and being aware of it can help make sure that, as we transition to renewable sources of energy, we’re not solving one problem while creating another.

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Nathan Schock (@nathanschock) is the director of public affairs and corporate social responsibility for POET, one of the largest producers of ethanol in the world. The 25-year-old company also operates a pilot-scale cellulosic ethanol plant, which uses corn cobs, leaves, husk and some stalk as feedstock, and expects to commercialize the process in Emmetsburg, Iowa through its joint venture with Royal DSM. For more information, visit http://www.poet.com.