At a recent session during WEFTEC 2025 on advances in ultraviolet (UV) disinfection, John Crawford, technical fellow – wastewater at BECA Consultants, highlighted an emerging technology developed in New Zealand that could help utilities treat some of the toughest effluents.
Crawford, who has more than 40 years of wastewater experience, presented on a supercritical UV disinfection system designed by Professor Andy Shilton and his team at Massey University. Unlike conventional UV systems, which typically operate with path lengths up to roughly 2-inches (50mm), the supercritical system reduces that distance to roughly .08- to .24-inches (2- to 6mm). The result is an exponentially greater UV transmission through waters with low UV transmittance (UVT), where conventional systems often fail, according to Crawford.
“The problem we’re trying to solve is the disinfection of difficult effluents – waters with particulates, dissolved organics and metals that shield pathogens from UV light,” Crawford said during his presentation. “By reducing the path length to just a few millimeters, the transmitted light intensity increases exponentially. That’s the fundamental advantage of this system.”
Only one technology is currently on the market, according to Crawford, and is containerized, modular and uses flat trays of low-pressure UV lamps. It has already been piloted and adopted at several small plants in New Zealand, including:
- A seaside resort community of 1,200-3,000 people achieved E. coli compliance despite high suspended solids (TSS).
- A roughly 2.4 MGD (9 MLD) meat processing facility consistently met discharge limits (<1,000 CFU/100 mL) with UVT as low as 10%.
- An ocean discharge site maintained compliance with UVT ranging between 10-14%.
Operators reported that the system is simple to maintain. “Operators told me they just use supermarket cleaners and a bit of citric acid,” Crawford said.
While the system isn’t intended to replace conventional UV systems across the board, Crawford stated it could serve a valuable niche. He also noted that conventional UV treatment will outperform the new technology in systems with high UVT – above roughly 60% UVT.
“I have zero commercial interest in this system. I’m simply a normal user of conventional UV,” Crawford said. "But I believe this technology deserves another look.”
