Photography by Hope Chang
At two of Yale’s residential colleges, an innovative machine is harnessing basic chemistry to achieve a new kind of green cleaning.
Since 2022, the custodial team at Benjamin Franklin and Pauli Murray colleges has been using a machine called the Annihilare AoS-500, which uses water, salt, and electricity to dispense a menu of solutions for cleaning, sanitizing, and disinfecting.
The machine is just one component in Yale’s campuswide approach to green cleaning, which aims to reduce the exposure of the campus community to chemical, biological, and particulate matter that may be harmful to human health and the environment. And so far, it has impressed the custodial staff at Franklin and Murray.
“The machine is a one-stop-shop cleaning system that is healthy and sustainable for custodial staff, our students, and the community,” says Kirsta MacLellan, the Yale Facilities superintendent at Franklin and Murray. “It has saved us time and money—and with less frequent ordering of different cleaning chemicals, we have fewer deliveries and have eliminated packaging waste.”
How it works
The Annihilare machine works by dissolving table salt in water, then electrifying the liquid to split the salt and water molecules so they can be rearranged to form two new solutions: hypochlorous acid (HOCl) and sodium hydroxide (NaOH). This weak acid is an effective germ-killer that, when mixed to 500 parts per million, is a hospital-grade disinfectant. Sodium hydroxide, commonly referred to as lye or caustic soda, makes an excellent cleaner and degreaser.
MacLellan says the Annihilare offers a non-toxic, sustainable alternative to chemical cleaners and notes that its solutions are Green Seal certified and registered with the U.S. Environmental Protection Agency, meaning they underwent the same third-party testing as other disinfectants on the market.
That is comforting to college residents like Arohi Nair, a sophomore in Pauli Murray College. “I have a friend who is very sensitive to chemicals so I am glad green cleaning is being valued in this way,” she says.
Finding the right solution
The Annihilare system produces six different solutions for cleaning, sanitizing, and disinfecting. The machine is compact—it fits into a closet—and is easy to operate, MacLellan says.
The machine is used daily for all of the colleges’ cleaning needs. The custodial team fills up spray bottles to clean bathrooms, activity spaces, fitness centers, and stairs. It is also used in floor cleaning machines and in mop buckets.
Testing for quality control
Two to three times per month, custodians use test strips for quality control. They dip a test strip into the bottle, wait for a color to appear, then check it against a reference chart posted next to the machine.
A blue strip indicates that the disinfectant has the desired pH level—and will work as intended.
Unlike chlorine bleach, which has a negative electrical charge, hypochlorous acid has a neutral charge. So rather than repelling germs that have negative charges in their cell walls or viral envelopes, HOCl readily diffuses into pathogens where it can then destroy them from the inside out—a process likened to a Trojan Horse.
As a result, HOCl is 80 to 200 times more effective than bleach at the same concentration while being non-toxic to humans and non-corrosive to surfaces due to its relatively neutral pH.
Many applications
The other type of solution produced by this process is sodium hydroxide—an odorless compound that is a byproduct of electrolyzed water. This saline solution makes an effective cleaner for glass, chrome, and stainless surfaces.
The machine also produces an all-purpose solution that is used to clean floors throughout the colleges. One downside of hypochlorous acid is that it’s not shelf stable— it will break down over time into non-hazardous saltwater. The Annihilare machine solves for that by generating cleaning solutions on demand. It’s a more sustainable approach to cleaning that eliminates the transportation emissions and waste that would come from product deliveries.
The cleaning solutions are odorless, explains MacLellan, which has led some to wonder whether they are actually effective at killing germs. In fact, fragrances in cleaning agents often result from chemicals that are harmful upon inhalation, such as volatile organic compounds (VOCs). Before purchasing the machine, MacLellan researched green cleaning options and found that Annihilare offered the right blend of effectiveness, convenience, and cost for Franklin and Murray colleges’ needs.
For their part, the Franklin and Murray custodial team are pleased with the system. “The Annihilare is effective and very easy to use,” says custodian Tamara DeBerry. “It’s a much healthier cleaning system for our team.” Pictured from left are DeBerry and custodians Cindy Martinez and Ashton “AJ” Johnson. Martinez and Johnson have been at Franklin and Murray since the building opened in 2017.
