Against the Flow

January 11, 2012

Reading time min

Brian Stauffer

In Stanford's science and medical labs, equipment such as glassware and surgical instruments must be zapped within an inch of its life to be made sterile for reuse. That process normally wastes a small ocean of water. But by installing a simple device on its sterilization equipment, the University is saving some 93,000 gallons of water a day from running down the drain.

That's important not just because it benefits the environment and saves money: the General Use Permit issued by Santa Clara County requires Stanford to keep water consumption within a ration of 3 million gallons daily. To accommodate campus expansion, the University must continually look for water-saving measures.

Why was so much water being wasted in the labs? Sterilizers, also known as autoclaves, use scalding, pressurized steam to kill bacteria and microbes, thereby creating condensate that can exceed 140 degrees C. Because the hot condensate can melt pipes, it must be tempered with cold water before it goes down the drain.

“The problem is that most sterilizers have been designed to have water pouring through them constantly, 24/7, to be available to cool the condensate whether the sterilizer is being used or not,” says Marty Laporte, associate director of utilities for water resources and environmental quality. Sterilizers typically run eight to 12 hours on weekdays, so there were many hours when the tap water was running for no reason. Multiply that by the more than 60 autoclaves on campus, all guzzling H2O in similar fashion, and you've got a conservation challenge.

Enter the Water-Mizer. When Gary Malinverno, facilities engineer for the School of Medicine, first heard about the benefits of the new device in 2003, it didn't take much to convince Laporte to include its installation in campus water conservation plans.

The Water-Mizer looks like a mini oil burner; it's less than a foot long and can easily be installed under an autoclave. The steam condensate discharged from the sterilization equipment enters the device through a tube in the top. When a temperature-actuated valve senses the presence of the hot mixture, then, and only then, does it let water in to cool the condensate. The tempered water is then ushered through the side outlet for safe discharge into the sanitary sewer system. When the sterilizer is not in use, the Water-Mizer's valves prevent water from running through the system.

“The Water-Mizer has had amazing results, and yet it's an extremely simple design—completely heat-activated, which means it uses no electricity,” Malinverno says.

It cost $113,000 to install 63 Water-Mizers in 14 buildings housing medicine, chemical engineering, biology, chemistry and bioengineering, resulting in a savings of nearly 34 million gallons of water a year. “It's been quite cost-efficient,” says Laporte.

“The amount we conserve with the Water-Mizers and other water-saving measures allows us to stretch our water supply so that we can continue to have enough water for new academic facilities.”

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