Energy’s Water Footprint

- 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.