Try explaining to your children, as I have with mine, that turning on a light is akin to running a faucet. You’ll likely get a confused look, but this is perhaps the simplest example of the relationship between water and energy (the “nexus”). It’s only one side of the coin, however. Water and wastewater operators experience the other side, chewing through electricity (and their budgets) to treat and transport water.
Resources being a scarce commodity, it’s incumbent upon us to optimize the use of water and energy as best we can. While conservation is the prime course of action for the public, the best solution for utilities may be to work smarter — by having the water-energy nexus work for us instead of against us. One trending way to do this is by “co-locating” water/wastewater treatment and power generation at a single facility. Described below are two examples of co-location … and innovation.
Combined Heat And Power (CHP)
DC Water in Washington, D.C., is among the most forward-looking, innovative utilities in the U.S., proving it once again by constructing the world’s largest combined heat and power (CHP) plant at its Blue Plains facility. CHP, also called cogeneration, uses a heat engine — a system that converts heat or thermal energy to mechanical energy — to simultaneously generate electricity and useful heat. Blue Plains will take heat from the 370 MGD of effluent it receives and turn it into 10 megawatts of off-grid electricity. The $450-million project relies on thermal hydrolysis, a process that pressure-cooks the waste before microbes convert it into methane in digesters. The methane powers turbines to generate electricity, while heat captured off the turbines is recycled into the thermal hydrolysis process. According to DC Water General Manager George Hawkins, the project will save the utility $10 million per year once completed (due this summer).
Combined Power And Desalination
Combined power and desalination plants, or hybrid desalination plants, produce drinking water and electricity by aligning the processes side by side; waste heat from the power plant is used as the heat source for desalination. Ideal for arid regions prone to drought (pay attention, California), it makes sense that the first such facility was built at Qidfa’, Fujairah, in the United Arab Emirates, completed in 2004 for $1.2 billion. The Fujairah plant recently approved an upgrade that will further take advantage of the water-energy nexus by capturing residual energy from the reverse osmosis process, which pumps seawater through membranes at pressures as high as 70 bar. Special rotary devices will harness and return the energy to the pumps for more sustainable, cost-effective operation. Other hybrid desalination plants have been constructed throughout the Middle East, but Fujairah remains the leader. As the cost for the notoriously high energy-spend of desalination is improved, and as desalination becomes more of a necessity, this type of co-location is sure to become more common.
Nexus Gains Steam In The U.S.
Here in the U.S., we are voracious (but improving) consumers of both water and electricity, having been blessed for so long with a cheap, abundant supply of each. We have begun to feel the pinch, however, as population and demand grows. Some of our fastest-growing cities are also the driest, exacerbating the problems posed by water scarcity and the water-energy nexus. In response, California, Arizona, and Nevada have enacted statutes that specifically mention the appropriation of water for generating electricity, according to the National Conference of State Legislatures. Because citizens are being affected, politicians are reacting to a problem that utilities have seen for some time. By working together — with politicians and with each other — utilities can still be at the forefront of a solution. Some already are. Who’s next?
Image credit: "https://creativecommons.org/licenses/by-nd/2.0/," © 2008 Tony Fischer Photography, used under an Attribution-NoDerivs 2.0 Generic license: