Making Water Service Energy-Neutral

March 24, 2016
Danfoss Drives explains how to reduce energy consumption in water production and treatment, enabling water plants to produce a net surplus of energy and reduce their CO2 footprint.

Global water crises—whether too much water or not enough—have for several years figured prominently on the list of threats facing our planet, according to the World Economic Forum’s Global Risks report. Other risks on the list, which ranks the impact on economies, environments and people, are also tied to a slew of other water-related issues.

Food, meanwhile, is heavily dependent on there being water available. “California will drop 30 percent in food production in 10 years if they keep going the way they are, simply because they don’t have enough water,” noted Mads Warming, global director of water and wastewater for Danfoss Drives.

Warming was speaking at this year’s Danfoss Drives conference in New Orleans about imagining a water industry that is energy-neutral. Under current conditions, not only are some power stations decreasing electricity production because they don’t have enough water, but the water/wastewater industry is highly dependent on energy as well. Wastewater is the third largest industrial end user of energy after chemicals and primary metals, Warming said.

“The energy neutrality concept is a lot more than optimizing a wastewater facility,” Warming said. “It’s about being a lot more intelligent about what you do from an energy point of view.”

Typically, water and wastewater treatment processes account for 25-40 percent of a local municipality’s electricity consumption. With energy reduction in water production, water distribution, wastewater pumping and wastewater treatment, combined with increased energy production from the wastewater treatment process, water service companies can achieve energy neutrality.

By introducing AC drives into water production, for example, water service companies have been able to achieve 20-45 percent energy reduction, Warming said. With optimized pressure management, water distribution has seen 20-40 percent energy reduction, as well as 20-40 percent leakage reduction.

Leakage management can be important, with water service organizations typically facing significant water losses from leaking pipes, Warming said. In one case in Asia, he saw leakage as high as 85 percent. “So 85 percent of the water was not reaching customers because of a leak,” he added.

Installation of more pumps and drives in 112 systems in 10 different countries demonstrated a typical leakage reduction of 38 percent. Other benefits included energy consumption reduced by 20-40 percent, extended pipe lifetime of 10-20 years, and fewer network-related complaints.

In wastewater pumping, a key to achieving 5-25 percent energy reduction has been keeping pumps clean. To combat pumps clogging over time, causing efficiency to drop, Danfoss has incorporated a de-ragging function into its drive. When necessary, the drive can turn the pump’s propeller the opposite way to let the pump clean itself, Warming explained.

The drive is the key element in improving efficiencies in wastewater treatment also, regulating low-load and high-load activities to reduce energy use by 25-60 percent.

On the flip side of various energy reductions is increased energy production of 20-60 percent by wastewater treatment facilities. “If you do wastewater treatment right, you not only reduce energy consumption, but also increase sludge, which helps you produce more energy,” Warming said.

Danfoss has shown a significant ability to produce more energy than is needed to treat the wastewater—a 92 percent net surplus in a case that Warming detailed for conference attendees. The Marselisborg wastewater treatment plant in Aarhus, Denmark, has been working since 2010 to transform its operations to minimize energy consumed and maximize energy produced. With a focus on process control, Marselisborg has put efforts into optimizing the nitrogen removal process with online sensor control; upgrading its blower technology to a high-speed turbo blower; controlling aerobic sludge as a function of temperature and load on the plant; and upgrading the combined heat and power (CHP) process for energy production, with 90 percent energy efficiency.

Marselisborg uses Danfoss VLT drives at every point in the plant, always looking for the ideal operating point. The plant has achieved its excess production of both energy and heat through a combination of AC drives on all rotating equipment, highly efficient components, computer control based on online sensors, deep process know-how, and CHP installation, Warming said. “After half a year, they were 98 percent of the time operating at the highest level,” he added.

Danfoss is also in close collaboration with Chicago’s water operations through the Water Technology Alliance (WTA), an organization that helps Danish companies enter or grow activities in the North American water and wastewater market.

“In Chicago, we’re expecting to invest $25 million,” Warming said. “We came up with a solution where we don’t have to expand the facility at all. Instead, we coped with demands from the EPA and at the same time turned energy use into energy production, for a cost of $3-4 million. It’s thinking differently instead of just expanding.”

Warming emphasized the importance of installing energy-efficient AC drives, and said that Danfoss’s VLT Aqua drive can save up to 25 percent of the AC drive investment in the first year vs. the next best alternative. He pointed to its energy-efficient variable-speed drive (VSD) design, intelligent heat management, automation adaption to the application, energy-efficient harmonic mitigation, and optimal control of all motors.

“If you purchase low-efficiency pumps, you will never get energy neutrality,” Warming said. With 0.5-4 percent better efficiency, he contends that switching to VLT Aqua drives gives the same or better efficiency gain as choosing an IE3 motor over an IE2 motor (an improvement of 0.9 percent).

“Real energy decoupling is possible. Energy-neutral utilities do exist,” Warming said. “Some are now calling wastewater treatment plants a biorefinery. It can be turned into a resource. They can get the money out of wastewater and reduce CO2.”

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