Study Finds Water Use for Switchgrass Ethanol Production Approximately the Same as for Gasoline
23 August 2009
|Consumptive freshwater use for ethanol and petroleum gasoline production. Data: Wu, ANL/ESD/09-1. Click to enlarge.|
In the US, producing one gallon of ethanol from switchgrass consumes approximately the same net amount of water as does producing a gallon of gasoline from conventional crude or oil sands oil, according to a study by Argonne National Laboratory researchers presented at the 238th national meeting of the American Chemical Society last week.
The production of both bio and petroleum feedstocks and fuels requires substantial water input. Biofuel feedstocks such as corn, switchgrass, and agricultural residues need water for growth and conversion to ethanol; petroleum feedstocks such as crude oil and oil sands also require large volumes of water for drilling, extraction, and conversion into petroleum products. In many cases, the Argonne team noted, crude oil production is increasingly water dependent.
Competing uses strain available water resources and raise the specter of resource depletion and environmental degradation. Water management has become a key feature of existing projects and a potential issue in new ones.—Wu et al. ANL/ESD/09-1
|Consumptive freshwater use for switchgrass ethanol and petroleum gasoline production. Data: Wu, ANL/ESD/09-1. Click to enlarge.|
The work examined the growing issue of water use in energy production by characterizing current net consumptive water use in bioethanol produced from corn and from cellulosic feedstocks, gasoline from Canadian oil sands, Saudi Arabian crude, and US conventional crude from onshore wells. The Argonne researchers evaluated water requirements and consumption for two major production stages: feedstock production and feedstock conversion.
The study focused on three USDA farming regions for the production of corn in the United States, in which 89% of corn and 95% of ethanol are produced. For petroleum oil, they selected regions representing 90% of US onshore crude production and 81% of refinery output, 100% of Canadian oil sands production, and 52% of Saudi Arabian oil production. The analysis takes into account regional variations and historic trends in water consumption for the selected fuels.
They examined corn ethanol produced via dry milling and cellulosic ethanol produced via biochemical and thermochemical conversion technologies. The analysis revealed that the amount of irrigation water used to grow biofuel feedstocks varies significantly from one region to another and that water consumption for biofuel production varies with processing technology.
Our study underscores that one of the benefits of using perennial biomass crops, such as switchgrass, is lower water consumption.—May Wu
Other findings included:
Consumptive water use for feedstock and fuel production varies considerably by region, type of feedstock, soil and climatic condition, and production technology for ethanol, as well as by age of oil well, recovery technology, and extent of produced-water reinjection and steam recycling for petroleum gasoline. There are significant regional differences, however, particularly for corn production.
Conservation measures to reduce consumptive water use are needed to achieve sustainable ethanol and gasoline production. Improved water management is needed for corn irrigation, particularly in those areas where water is scarce. Cellulosic feedstocks may need to be grown in their native habitat to reduce irrigation. Groundwater use and management are especially critical in arid regions and in locations with high concentrations of biofuel or oil production facilities.
In fuel-production facilities, both petroleum gasoline and starch-based ethanol consume little water as a result of historically persistent efforts toward water optimization. For example, ethanol-producing facilities have reduced water consumption by 48% during the past 10 years. This trend is likely to continue and could result in facilities that effectively use net-zero water, at least in some locations in the foreseeable future.
Water consumption can be reduced by increasing the use of such measures as steam condensate reuse and treated process water recycling, and by implementing process modifications by means of existing commercial technologies. For cellulosic biorefineries, an integrated process that optimized for water use should be encouraged. Finally, the use of produced-water re-injection for oil recovery should be increased.
Groundwater management is extremely important in arid regions and in locations with high concentrations of biofuel or oil production facilities, where a rapid increase in water demand as a result of growing energy demand could have a compounded impact on resources and the environment.
The energy industry is a major consumer of water. As shown in this analysis, consumptive water use varies by process, region, and technology. How a rapid increase of consumptive water use affects water quality is less clear...nutrient releases and toxic contaminant leakage into waterways (surface water and groundwater) can have devastating environmental impacts and, production process discharges have distinctive chemical profiles that can affect downstream wastewater treatment needs, opportunities for treated wastewater recycling, and final solids disposal. At the extreme, degraded water quality can also affect the treatment needed for input water.
Although the required quality of input water varies with type of fuel and feedstock, agricultural crops and biofuel feedstocks generally require higher quality water than that needed for oil E&P (for example, injection water for oil recovery can allow higher levels of total dissolved solids than irrigation water for crops). A study is underway to access potential synergies from using contaminated groundwater for biofuel development. Further investigations will address the impacts on water quality due to various liquid-fuel production processes not only from individual projects, but also from multiple projects for entire regions and over extended periods.—Wu et al. ANL/ESD/09-1
Projected consumption in 2030. A separate study from Argonne presented at the ACS meeting estimated and compared projected amounts of domestic freshwater consumed in the production of biofuels with the amounts consumed in the production of fossil fuels, electricity generation, and non-energy sectors.
This study found that while total US water consumption is expected to increase by 20% over the 2005-2030 time period, water consumption for energy production is projected to increase by more than 150%, and water consumption for biofuels (biodiesel, corn-based ethanol, and cellulosic ethanol) production is projected to increase by more than 300%. Most of the water consumed in biofuels production (about 70%) is projected to be for corn-based ethanol, with most of this amount for crop irrigation. Between now and 2030, the West North Central Region of the United States is expected to consume the highest amount of water for biofuels production.
The water projected to be consumed in producing corn-based ethanol in 2030—nearly 19 billion gallons per day—is about the same as that projected to be consumed by industrial and commercial production, domestic and public use, and livestock watering combined.
May M. Wu, Marianne Mintz, Michael Wang, and Salil Arora. Water consumption in the production of bioethanol and petroleum gasoline (ACS 238, FUEL 309)
M. Wu, M. Mintz, M. Wang, and S. Arora (2009) Consumptive Water Use in the Production of Ethanol and Petroleum Gasoline (ANL/ESD/09-1)
Deborah Elcock. Projected water consumption for ethanol and biodiesel production relative to other sectors in 2030 (ACS 238, FUEL 308)
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