Public health is threatened by a wide variety of pathogenic water contamination. Seeking efficient water disinfection approaches is of great significance, but traditional methods of disinfection cause their own environmental problems. Chlorine is cheap and easy to use in centralized water systems but at the expense of harmful chemical byproducts.
Now, researchers at the Georgia Institute of Technology have found a way to use small shocks of electricity to disinfect water, reducing energy consumption, cost, and environmental impact. The technology could be integrated into the electric grid or even powered by batteries.
“This is a pretty new disinfection technology, and we want to demonstrate on a small scale first and then improve its real-world applications for point-of-use or off-grid water purification,” said Xing Xie, the Carlton S. Wilder Assistant Professor in the School of Civil and Environmental Engineering.
Even though conventional electric field treatment (CEFT) is applied for food pasteurization, it hasn’t been widely used for drinking water disinfection because of the relatively high cost. The bacteria cell membrane acts like a capacitor in a circuit when water and bacteria are exposed to electricity. Normally, in CEFT, water’s low conductivity means nanosecond pulses won’t charge the membrane fast enough to kill bacteria.
The researchers created a locally enhanced electric field (LEEFT) that brought the electricity directly to the bacteria. The electrodes have gold nanotips that build up concentrated charges instantly when connected to electricity, enabling the charges to travel to the membrane and kill the bacteria much faster.
“This ultra-fast bacteria inactivation just using the nanosecond pulses is a surprise because, theoretically, nanosecond pulses are just too short of killing the bacteria in conventional electric field treatment because the membrane takes time to charge,” said Ting Wang, a postdoctoral researcher in School of Civil and Environmental Engineering (CE). “But with LEEFT’s nanowedges and nanostructures, the bacteria cells can be charged directly by the nanometal, quickly disinfecting water.”
Researchers fabricated gold nanowedges on the electrode edge of a chip in otrder to test the technology. They then added the model bacteria Staphylococcus to the chip, a commonly used bacteria in labs and often found in water systems. Next, electric pulses were applied, and the reaction of bacteria was watched in real-time using a microscope.
When the researchers applied electricity at 40 kilovolts per centimeter for 200 nanoseconds, they found 95% of nanowedges successfully killed the bacteria. Compared to conventional EFT, LEEFT reduces applied eclectic field strength by eight times – and shortens the treatment time by 1 million times.
“We found that even nanosecond pulses could kill the bacteria in the LEEFT and not other circumstances,” Wang said.
The researchers said that this near-instantaneous decontamination reduces how much electricity is needed to disinfect water, making this an affordable sanitation option and pointing to a future in which producing clean water may take less of a toll on the environment.
- Ting Wang and Xing Xie. Nanosecond bacteria inactivation realized by locally enhanced electric field treatment. Nature Water, 2023; DOI: 10.1038/s44221-022-00003-2