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The energy-water collision

In the United States power plants account for 41 percent of the country’s freshwater needs. In fact, according to the Union of Concerned Scientists, more water is withdrawn for cooling power plants than for any other use, with agriculture coming second (37 percent), and drinking water third (13 percent). With rising energy consumption and shrinking water resources, communities are already facing so-called “energy-water collisions.” An integrated approach and new energy-efficient technology may provide a partial solution.

The equation of the energy-water nexus is simple: it takes water to make energy, and it takes energy to treat and transport water. Yet with the massive amounts of energy and water involved, the situation has become increasingly complicated – and extremely costly. The amount of water needed for cooling in power plants in the US for one minute, for example, is equivalent to three times the amount of water that flows over Niagra Falls in a single minute, that is, three times 168,000 cubic meters (6 million cubic feet).

Europe faces similar challenges. According to the European Environment Agency, 37 percent of Europe’s freshwater abstraction is for cooling in energy production, and Germany, France, and Poland use more than half of their total abstracted water for energy production. These high percentages are a cause for concern, since the agency estimates that 19.5 percent of Europe’s population lives in water-stressed countries.

High energy use, high freshwater use, and limited water resources can result in what the Union of Concerned Scientists calls “energy-water collisions.” For example, recently in drought-stricken areas of the US, some power plants have been forced to operate at reduced capacity due to a lack of water.

Energy for treating and transporting water

The amount of energy used to treat and transport water is also staggering – approximately 20 percent of a city’s total energy consumption. Similarly, a 2005 California Energy Commission study found that 19 percent of the state’s electricity usage was water related, including transporting water, wastewater treatment, and agriculture, residential, commercial and industrial use.

Not only is the amount of energy needed to treat and transport water high, but failing infrastructure also leads to massive waste. Many cities in the US, for example, lose between 30 and 50 percent of their treated potablewater through inefficient and old infrastructure systems.

Energy costs of wastewater treatment

Wastewater treatment is one area where there is significant potential to reduce energy usage. According to The California Energy Commission, the state’s primary energy policy and planning agency, energy represents the largest controllable cost of providing water or wastewater services to the public.

The commission’s Energy-Water Connection project states, “Most facilities were designed and built when energy costs were not a concern. If you have not fully investigated the applicability of modern technology, you probably are wasting a large amount of money without realizing it.”

Huge amounts of energy, for example, are used during the biological/secondary wastewater treatment process where aeration is often used instead of chemicals. Sometimes, injecting air into the water can account for as much as 60 percent of the energy consumption of a plant.

“Looking back over the last five years, the output of most wastewater treatment plants has remained the same but electricity costs have doubled,” says Johan Grön, Xylem’s Chief Technology Officer. “During the next 10 years electricity costs will most likely continue to rise, so rethinking water and energy from an integrated city planning approach could be very beneficial financially.”

Investing in new solutions

Though many cities recognize the need for improving infrastructure and lowering energy costs, some have been reluctant to try new technology and solutions.

“While most cities would agree that, financially, the investments make sense, many feel there’s not enough reliable data yet available to prove that making energy-saving investments today will pay off in the long run,” Grön says. “They’re also a bit hesitant when it comes to dealing with new technologies, which requires us to take a different approach towards implementing them. Scaling up and testing new technologies becomes even more important to ensure reliability.”

As part of its commitment to testing, Xylem recently participated in a process reengineering project at the Sternö wastewater treatment plant in Karlshamn, Sweden. Its aeration system accounted for 44 percent of the plant’s total energy consumption. By installing a monitoring control system, replacing tube aeration with disc diffusers and lobe blowers with efficient screw type versions, the plant reduced its energy consumption by an impressive 13 percent. The payback on the investment is expected within four years.

“Things are changing,” says Grön. “Cities are starting to access data about the cost of providing water and increase their awareness of the improvement opportunities available to them.”

A water-smart energy future

More efficient technology will be an essential part of solving the water-energy problem, according to a report from the Energy and Water in a Warming World Initiative. Its 2011 report “Freshwater Use by U.S. Power Plants” states that “developers and utilities are reducing the risk of energy-water collisions by choosing technologies that use essentially no water, such as wind and solar photovoltaics, and by investing in energy efficiency.”

For example the Ivanpah Solar Electric Generating System, a 370-megawatt power plant being built in the California Mojave Desert, uses dry cooling technology that will use 90 percent less water per unit of electricity compared to wet cooling plants of the same type. Another power plant in Amarillo, Texas, solved its water scarcity problem by switching to treated wastewater for cooling.

“Every time we build a power plant, we’re making decisions that last for decades,” said Peter Frumhoff, head of the scientific advisory committee for the report. “By investing in power plants that are efficient, use low-water cooling and produce little or no carbon emissions, utilities and plant owners can help protect the water resources our kids and grandkids will depend on.”

by Alannah Eames