NICE3: Ultrasonic Dishwashing Reduces Wastewater and NOx Emissions

A joint cost-sharing grant program of:
U.S. Department of Energy's Office of Industrial Technologies and Office of Technical and Financial Assistance
U.S. Environmental Protection Agency's Office of Pollution Prevention

Produced by the National Renewable Energy Laboratory,
a laboratory of the U.S. Department of Energy
1000 Independence Ave., SW
Washington, DC 20586

Retirement homes, restaurants, universities, hospitals, and other institutional kitchens are mandated by state and county health departments to use commercial dishwashers. The ommercial dishwashing technology that is used worldwide today in more than 4 million units was developed in the late 1800s. These dishwashers user large volumes of high-temperature, highly pressurized water, plus strong detergents to adequately clean dishes.

With the assistance of a grant from NICE3, a program of the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency, Ultrasonic Products, Inc. (UPI) is developing and testing an ultrasonic dishwashing technology that uses lower temperature water and less detergent, resulting in energy savings, wastewater reduction, and a reduction of NOx emissions.

• Challenge: Water temperatures required for commercial dishwashing range from 140 degrees - 160 degrees F (60 degrees to 71 degrees C), with sanitized rinsing at 180 degrees F (82 degrees C). Even with these high temperatures, some materials such as lipstick still cannot be adequately removed from drinking glasses. An alternative is needed to reduce the amount of energy, water, and detergent now required for effective cleaning.

• Solution: In 1990, Southern California Edison (SCE) demonstrated an ultrasonic dishwashing machine, designed by UPI, that used water at a much lower temperature and with far less detergent. Several months later, SCE commissioned a report to identify technologies that would have a positive environmental impact, particularly through energy savings and abatement of NOx emissions. SCE's report found the ultrasonic dishwashing technology designed by UPI to have the greatest potential for savings.

  The new dishwashing process operates at a lower water temperature (100 degrees F [38 degrees C]), uses no strong detergents, requires much less water, generates less wastewater, and reduces the amount of dish breakage from thermal stress. The technology, which UPI has patented and registered globally, utilizes an ultrasonic transducer that can be molded into the shape that best fits the geometry of the dishwashing unit. The transducer generates sound waves that result in micro-bubbles imploding on the dish surface at a rate of 40,000 times per second. The mechanical scrubbing and cleaning action derived from this implosion allows cooler water to be used. This new system is also omnidirectional, allowing waves to permeate into the interior of objects with no "dead spots."

  The University of California at Santa Barbara is currently conducting industrial tests of this ultrasonic dishwashing technology to verify its efficiency and effectiveness. Depending on these tests and market conditions, UPI's technology could be adopted around the world. In fact, licensees in North America, Europe, and Asia have already expressed interest in marketing the product.

• Energy Savings: Assuming the new technology has a market penetration rate of 15% for new dishwashers (currently about 19,000 units are purchased each year) annual U.S. energy savings could reach 1.42 trillion Btu (1.5 quadrillion joules). Over time, as older units are replaced, annual energy savings could increase by a factor of 10.

• Environmental Benefits: With a market penetration of 15%, the new technology would reduce wastewater by an estimated 1.42 billion gal (5.37 billion liters) nationwide. In addition, 8.2 million lb (3.7 million kg) of NOx emissions can be prevented each year since the electric demand and power generation required for the current dishwashing technology would be reduced. The new technology would also drastically reduce the use of harsh, caustic detergents.

• Economic Savings: With a market penetration of 15%, operators of commercial dishwashers could save $14.2 million annually from reduced energy use.

• Applications: This technology can be applied to commercial dishwashing applications around the world in a variety of institutional environments.