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Energy's Water Footprint

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- by Mike Ewall, Energy Justice Network

In 2005, thermoelectric power plants (nuclear, coal, oil, gas and trash/biomass incinerators) were responsible for 41% of all freshwater withdrawals and 49% of total water withdrawals (including oceans and brackish waters) in the U.S. Much of this water (mainly used for cooling) is returned to local water bodies, but at a higher temperature, which can be harmful to aquatic life. A large portion is also evaporated, so total water consumption is still quite significant.

These thermoelectric power plants consume an average of 800 gallons per megawatthour, ranging from 600 to 1,100 gal/MWh.  This means that a 500 megawatt power plant running at 90% capacity would use 2.4 to 4.4 Billion gallons of water each year for cooling.  About 85% of this is evaporated, draining rivers and aquifers. The balance is returned to the river as a heated solution containing concentrated pollutants like aluminum and phosphorus.

Some biomass incinerators have sought to use sewage effluent (the liquids that are separated out at a sewage treatment plant) as cooling water. Sewage effluent is a highly contaminated solution containing disinfection byproducts, metals and numerous classes of discarded and excreted biologically active chemicals such as active pharmaceutical ingredients and personal care products, endocrine disrupting compounds, mutagenic cytotoxins and others. These pollutants can contaminate the air when that water is evaporated. Whatever isn’t evaporated will concentrated in the wastewater that the biomass facilities release into local water bodies.

Air cooling is an alternative to water-based cooling, but is noisier and more expensive. Some state regulators have allowed water cooling based on company claims that air cooling is cost prohibitive.

Growing crop-based biomass also requires a lot of water. The biomass industry favors trees and wood waste it doesn’t have to grow, but of the available energy crops, quick-growing, high-yield plants like Miscanthus are preferred. Such crops are also quite demanding. 

A review of the Miscanthus-burning biomass incinerator proposed for Jasper, Indianafound that Miscanthus is a thirsty crop, requiring irrigation in areas like Southern Indiana, where rainful is insufficient and global warming is worsening droughts. The research found that Miscanthus is not drought-tolerant, even for a single season, and that without irrigation, Miscanthus’ yields are variable/low. However, it is unlikely that irrigation of Miscanthus will be economically viable, since biomass production must be low cost and low input, and establishment of a Miscanthus crop requires expensive transplanting of plantlets.

Because Miscanthus has a deep, dense root mat, extending far deeper than corn roots, it sucks up more water and dries out soil more than corn or soy. European researchers have expressed concern that Miscanthus production may prevent ground water restoration and diminish groundwater.