Assessment of Freshwater Requirements and Conservation Options for the Production of Lignocellulosic and Algal Biofuels and Thermoelectriciy

Freshwater demand for energy production is a growing concern in the U.S. Cellulosic ethanol and algae-derived biodiesel/ bioethanol are promising biofuels as transportation fuels for the future. The National Research Council's 2008 study estimated that ~4 and ~9.5 gallons of freshwater will be required for a gallon of ethanol production from corn kernels and cellulosic biomass, respectively. When microalgae fully grow in fresh water, their maximum concentration is estimated to be less than 0.5% (wt). This future demand for water will be in competition with that from conventional power generators such as coal-fired power plants. The United States Geological Survey (USGS) estimated that U.S. thermoelectric power generation accounted for ~136 billion gallons per day (39%) of freshwater withdrawal in 2000, ranking only slightly behind agricultural irrigation.

In this presentation, we have analyzed the water quality and quantity requirements for cellulosic ethanol production with two feedstocks (i.e., switchgrass and corn stover) and two pre-treatment methods (i.e., dilute acid and ammonia fiber explosion methods) based on the literature. In addition, the research status of water utilization and wastewater generation from algae-derived biodiesel will also be presented. Many rivers in the western U.S. are undergoing river flow reductions under climate change, and thus many of the coal-fired power plants in the region are expected to undergo serious cooling water shortage problems. The quantity and quality of freshwater withdrawal and discharge from coal-fired power plants required for cooling water will also be discussed in this presentation. This comparative investigation of water consumption will pave the road for a comprehensive comparison of potential water resource impacts from energy production alternatives, namely, lignocellulosic biofuel, algae-derived biofuel, and coal-fired power electric plants in the hydrologic setting of the western U.S.