New tech cleans up water disinfection

Safe drinking water is essential for public health, but methods of disinfection can cause environmental problems; chlorine is cheap and easy to use in centralised water systems, but at the expense of harmful chemical by-products.

Now, researchers at Georgia Institute of Technology have presented a way to use small pulses 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, they said.

“This is a pretty new disinfection technology, and we want to demonstrate in the 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.

Xie and his postdoctoral researcher Ting Wang detailed their work in a paper published in Nature Water in January, 2023.

Although conventional electric field treatment (CEFT) is applied for food pastuerisation, it hasn’t been widely used for drinking water disinfection due to its cost. When water and bacteria are exposed to electricity, the bacteria cell membrane acts like a capacitor in a circuit. Typically in CEFT, water’s low conductivity means nanosecond pulses won’t charge the membrane fast enough to kill bacteria.

MORE IN ENERGY AND ENVIRONMENT

According to the team, they 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 to kill the bacteria in conventional electric field treatment because the membrane takes time to charge,” Wang said.

“But with LEEFT’s nanowedges and nanostructures, the bacteria cells can be charged directly by the nanometal, quickly disinfecting water.”

To test the technology, they fabricated gold nanowedges on the electrode edge of a chip. Then they added model bacteria Staphylococcus to the chip, a commonly used bacteria in labs and often found in water systems. Next, they applied electric pulses and watched how the bacteria reacted in real time under a microscope.

When electricity was applied at 40kV per cm for 200 nanoseconds, they reported that 95 per cent of nanowedges successfully killed the bacteria. Compared to conventional EFT, LEEFT lowers applied electric field strength by eight times and shortens the treatment time by one million times, they confirmed.

The team said that the near-instantaneous decontamination reduces how much electricity is needed to disinfect water, making it an affordable sanitation option and pointing to a future where producing clean water may take less of a toll on the environment.