Water falls

Even though the vast majority of the water used to produce biofuels comes in the form of irrigation water (see Concern over water rates), water consumption by biofuel plants is hardly insignificant. The average 50m-gallon-a-year bioethanol plant gets through around 400,000 gallons of water a day: the same water consumption as an 18-hole golf course or a town of 5,000 people.

Place enough biofuel plants in close proximity, as happens when biofuel plants congregate in specific agricultural regions, and you can quickly develop problems, especially if the region is already suffering from some measure of water scarcity. Already, plans to build several biofuel plants in the US have had to be abandoned because of difficulties obtaining sufficient water.

And the problem is only likely to get worse. According to a report produced by the US Institute for Agriculture and Trade Policy, the biofuel industry in Iowa utilised around 7% of the state’s industrial water supplies in 2006. By 2012, however, this figure is expected to rise to 14%. This kind of increase will probably be repeated in many other states.

To try to circumvent this problem – as well as to reduce costs – the US biofuel industry is continually looking at ways to reduce its water consumption. According to the US Renewable Fuels Association, the bioethanol industry has already reduced its water consumption from 6 gallons of water for each gallon of ethanol produced in the mid-1990s to 3.45 gallons of water today.

But the bioethanol industry wants to go further: to under 3 gallons of water. Biodiesel producers already utilise less water, at 1–2 gallons of water for each gallon of biodiesel. But they are now trying to remove the water entirely.

In conventional bioethanol production, around 30% of the water consumed is used directly in the ethanol production process: as steam to heat the raw corn or as liquid water to transform the subsequent corn mash into slurry. The remaining 70% isn’t used to produce the ethanol but is rather used in the boiler that provides heat for distillation and in the cooling towers. The bioethanol industry has found ways to reduce both types of water use.

For the water used directly in ethanol production, they have done this by developing improved fermentation processes, using novel enzymes and strains of yeast, that require less water. They are also recycling more of the water: for instance, some plants are heating the raw corn by passing the steam through metal coils rather than mixing it directly with the corn.

Recycling is also the main way in which bioethanol producers are reducing their consumption of water for non-production purposes. Some plants, such the bioethanol plant in Bingham Lake, Minnesota, operated by POET, the world’s largest ethanol producer, have developed these water recycling processes to such an extent that they no longer produce any waste water.

Another approach that some bioethanol plants, such as Corn Plus in Winnebago, Minnesota, are exploring is to utilise municipal waste water rather than supplies of fresh water. Such waste water has been treated sufficiently so that it can be discharged into rivers and other surface waters, but not enough for it to be used as potable (drinkable) water. With a bit more treatment, it should therefore be perfectly adequate for use by an ethanol plant.

Other bioethanol plants are using industrial waste water. For instance, POET’s bioethanol plant in Portland, Indiana, gets all of its water from a nearby quarry, while its plant in Big Stone, South Dakota, gets 80% of its water from the cooling ponds of a neighbouring power plant.

In biodiesel production, water is mainly used to wash the biodiesel in order to remove the liquid alkaline catalyst and various other impurities. A number of US biodiesel companies, such as Greenline Industries and HyPower Fuel, have now developed methods for removing the catalyst and impurities that don’t require water.

Greenline Industries has developed an ion-exchange resin that captures the catalyst and impurities, removing them from the biodiesel. HyPower Fuel has developed a version of the biodiesel production process that requires far less catalyst than the conventional process, entirely removing the need to wash the biodiesel with water.

The views represented here are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. or of the SCI.