New criteria for microbial reduction: Drinking water standard revision catches up with UV-LED

22-11-2019
UV-LED,UV technology,LED,wastewater treatment,water treatment

An international standard on drinking water treatment has been updated following developments and the roll-out of UV-LED (ultraviolet-light emitting diode) technology.

NSF International, the body accredited by the American National Standards Institute (ANSI), has established new criteria for the use of UV-LED technology for microbial reduction.

The standard covers treatment systems that use ultraviolet light to inactivate or kill bacteria, viruses and cysts in microbiologically unsafe water (Class A systems) or to reduce the amount of non-disease-causing bacteria in disinfected drinking water (Class B systems).

“While non-disinfecting LEDs are found in everyday applications such as lighting fixtures and consumer electronics, this use of ultraviolet LED technology is very different,” said Jessica Evans, director of standards development at NSF International.

“Lab testing shows that ultraviolet LED technology is effective at reducing bacteria and other types of microorganisms in drinking water.”

Addressing newer alternate UV technologies
The revision focuses on the standard: NSF/ANSI 55: Ultraviolet Microbiological Water Treatment Systems.

Initially developed in 1991, NSF/ANSI 55's scope was limited to low-pressure ultraviolet (UV) radiation systems using low-pressure mercury bulbs, which was the only technology available in the marketplace at the time.

In 2014, the Drinking Water Treatment Units Joint Committee responsible for the NSF/ANSI standard began developing a protocol to address newer alternate UV technologies.

After considering several options, an NSF task group recommended the approach of running a direct log-reduction test with an organism that would represent an entire class of organisms.

The task group concluded that the virus Q-beta is an acceptable surrogate to Rotavirus and the test method performs appropriately. This holds true at both ends of the UV wavelength range examined (254 nm to 285 nm), the NSF said.

Notable UV-LED developments
An industry source told Aquatech Global Events that the NSF had to “push hard on updating this standard in the face of inertia from many committee members representing legacy mercury-vapour lamp technology".

“NSF has done a great job in updating this standard to respond to new technology developments,” said Oliver Lawal, president of the International Ultraviolet Association (IUVA).

"They have successfully maintained the high technical bar of materials compatibility, structural integrity and microbiological efficacy while employing evaluation techniques that have been verified in large scale US-EPA drinking water certifications for over a decade. Specifically, the move to a log-inactivation of a verified surrogate is a move in the right direction for system benchmarking.”

While the majority of UV-LED development progress has been on a smaller scale, for point of use systems, one of the world’s largest UV-LED systems for municipal disinfection will be installed at United Utilities by UK-start up, Typhon Treatment.

Meanwhile, Japanese firm Metawater is scaling up its UV-LED solution, with the ambition to offer a 1,200 m3/day system.

The company signed an agreement with manufacturer Risui-Kagaku Co for the OEM supply of UV treatment equipment using UV-LED.

What does it mean for manufacturers?
The existing protocol for current systems will remain in NSF/ANSI 55 for at least five years, according to the NSF.

Manufacturers will have the option to evaluate their product to the new test method or the older test method defined within the standard. For devices with wavelengths other than 254 nm, the new method using Q-beta would be required and would have the following criteria:

  • 4-log reduction of Q-beta at the alarm set point for Class A devices
  • 1.5-log reduction of Q-beta for Class B with UV source irradiance at 70 per cent normal output or 2.14-log reduction with UV source irradiance at 100 per cent normal output.

As the final step in the standards development process, NSF/ANSI 55 was ratified by NSF’s Council of Public Health Consultants, which includes representatives from the U.S. EPA and the Centers for Disease Control and Prevention (CDC).