What in the World Is the Water Efficiency Equation?
By Cindy Wallis-Lage
Unlike Albert Einstein’s famous relativity equations or the Pythagorean Theorem, the water efficiency equation is neither famous nor constant. The specific factors and associated weights that determine water efficiency vary over time and even then are subjective. The best we can do to define the ever-evolving water efficiency equation and its corollary—the sustainability solution—is to share information about recognized factors.
Conservation, water reuse, energy reduction and recovery, innovative water treatment technologies, public education, and other factors contribute to water efficiency. To keep crucial points afloat in this sea of information, I’ll stick to the recovery of water and energy from used water.
If you think of a wastewater treatment plant as a resource recovery center (something we should all do), recovery of water, energy, nutrient, and biosolids resources can be justified both economically and environmentally. Water and energy are especially valuable resources to recover, even if the value of water is not fully recognized by the public because of artificially low user rates.
When it comes to reuse, there’s a way, but not always a will. Advanced treatment technologies make it possible to reclaim water to very high drinking water standards. But we can’t attain sustainable water management until we dispel political and public perceptions that water reclamation and reuse is unsafe or otherwise unacceptable. Education is a tool to help us eliminate the negative yuck factor in the water efficiency equation.
Industries frequently recycle water for use in the manufacturing process use. Local government, too, is increasingly tapping into reuse to supplement potable supplies. Examples are found around the world, especially in arid regions where water is in short supply. In the United States, water reuse has become an important part of water supply portfolios for many communities in the West, and parts of the South.
Orange County, CA, is expanding its successful Groundwater Replenishment System (GWRS), which is already the world’s largest wastewater purification system for indirect potable reuse, to produce water that exceeds all state and federal drinking water standards. The GWRS uses a three-step advanced treatment process to purify wastewater that otherwise would have been discharged into the Pacific Ocean. It enhances existing water supplies by providing a reliable, high-quality source of water to recharge the Orange County Groundwater Basin and protect the basin from further degradation due to seawater intrusion. The expansion will, upon expected completion in the fall of 2014, bring the total production of the GWRS to 100 million gallons per day, providing enough water for 850,000 people.
Energy Reduction and Recovery
Goals for energy efficiency can range from simply reducing energy consumption to the challenge of becoming energy-neutral (generating as much energy as consumed). Increasing automation and upgrading equipment to more energy efficient models are good starting points for utilities that want to reduce energy use. Improving efficiency of aeration and pumping—operations with the highest energy requirements—can especially yield significant energy savings. Wireless communications can facilitate better monitoring, control, and collection of more real-time consumption data—also leading to increased energy efficiency. Strategies for energy recovery are increasingly evaluated and implemented as more facilities seek to take advantage of the energy potential in water and wastewater operations to generate energy that they can use to power all or a portion of their own operations or sell to regional grids.
Water and wastewater treatment utilities are typically some of the biggest individual users of electricity, and publicly owned treatment works typically account for one-third of a municipality’s electricity consumption. Energy represents 25% to more than 50% of a utility’s operating costs, so cost savings through reduced energy use can be significant. But economics alone don’t drive decisions to reduce energy consumption. Rising energy needs, capital needs, facility size, incentives, and policies that target energy efficiency and energy reduction, social pressures and preferences, and changing treatment requirements and technologies also fuel the drive to use less energy.
Wastewater is a clean, renewable energy source, and small hydro opportunities exist for water, as well as wastewater utilities. Biogas production from the anaerobic digestion process can produce 15%, or more, of a wastewater treatment plant’s electricity. The East Bay Municipal Utility District in Oakland, CA, has become net producer of energy, helping demonstrate the Water Environment Federation’s assertion that the energy contained in wastewater exceeds the energy needed for treatment by several times. The district held a dedication ceremony in early April to celebrate its transition from electricity consumer to electricity producer. Accepting industrial-strength waste increased the district’s biogas production, and installation of an onsite biogas turbine earlier this year pushed the district past net zero into a positive position.
Energy produced at wastewater plants (e.g., biogas) can contribute to renewable energy supplies and reduce costs or generate revenue for wastewater utilities and local governments. Utilities are also increasingly harnessing the power of water to create energy by using excess hydraulic pressure to generate hydroelectric energy with small turbines.
Balancing the Equation
There is a delicate balance between water footprint and carbon footprint. Focusing on one element in isolation will not yield a balanced world. The benefits of reductions in water footprint may have off setting and more damaging impacts on carbon footprint and vice versa. Individual activities viewed in isolation may lead to decisions, which do not yield a balanced and sustainable environment. We may find that we cannot minimize water footprint and carbon footprint simultaneously. For example, growing crops for alternative fuels increases water demands. As another example, the technologies developed to help utilities meet stricter treatment standards and close widening gaps between demand and supply can lead to more energy consumption. Advanced water treatment technologies such as membrane filtration and ultraviolet disinfection enable reclamation and reuse as well as desalination, but tend to be energy-intensive. The current research and development focus on advanced treatment with reduced energy requirements is an example of the water industry’s effort to not only define, but also balance the total water efficiency equation.
Cindy Wallis-Lage is president of Black & Veatch’s global water business.