It takes water, lots of it, to produce energy, regardless of the process. A thermoelectric plant consumes 400 gallons or more per megawatt; producing a gallon of oil or gas uses 1.5 gallons of water. Biofuels are even more demanding, requiring 4 gallons to process a gallon of fuel; oil shale needs 2 to 3 gallons of water per gallon of oil extracted; and concentrating solar power can use up to 900 gallons of water per megawatt. Thermoelectric cooling is responsible for 41 percent of the country’s freshwater withdrawal. And some power plant construction projects are being held up due to available water scarcity.
It also takes energy to move, handle, and process water. Pumping water from 120 feet requires 540 kilowatts per million gallons pumped, and the deeper you go to get water, the more energy is needed to bring it to the surface, rising to 2,000 kilowatts per million gallons at a depth of 400 feet. Water and wastewater treatment systems account for about 35 percent of the energy used by municipalities.
Yet wastewater, with the biosolids it contains, has energy potential tied up in it, up to 12 times the energy used to treat it. This country’s more than 16,000 publicly owned wastewater treatment facilities produce more than 64 pounds of biosolids per person, per year, resulting in 7.2 million metric tons of “dry solids” annually. Every gallon of wastewater contains the equivalent of $1.88 worth of fertilizer, methane energy, and beneficial organic matter for soils, in addition to clean water. In a single example, the City of Palo Alto treatment plant has a calculated potential to generate $16.5 million a year in energy and by-products from its 24 million gallons per day of wastewater processed.
An example of a project that will take advantage of this co-dependence is a project in Kemper County, Mississippi. The project involves an integrated gasification combined cycle power plant that will use reclaimed water from two Meridian, MS, publicly owned treatment works (POTWs). The contract for the reclaimed effluent with Mississippi Power will generate significant income for the City of Meridian and Lauderdale County.
This could show the way for a new generation of power plants. A DOE study estimates that 81 percent of power plants proposed for construction have within a 10-mile radius one or two wastewater treatment plants which could provide sufficient cooling water supply. The same study estimates that 97 percent of plants could meet their cooling water needs with one or two such treatment plants within a 25-mile radius. The potential for economic and energy synergy is huge.
WWEMA (Water & Wastewater Equipment Manufacturers Association) has created a position paper, “The Water/Energy Nexus,” that makes this co-dependence case in much greater detail and from which many of the statistics in this article were drawn. Revere Control Systems, an independent control systems integrator with 30 years of experience in the water and wastewater industry, is an active member of WWEMA and a participant in their Water/Energy Nexus committee. We are actively seeking opportunities to apply our energy management technologies to water/wastewater projects and in the process to bring together technologies that will allow greater confluence of water and energy to the benefit of treatment plant operators, energy producers, municipal economies, and the environment.
Find out more about our energy management offering at our web site.
