Multi-wavelength UV technology for chemical-free total chlorine reduction in water treatment

Overview

This technology offers a chemical-free approach to total chlorine reduction in water treatment systems. By leveraging multi-wavelength ultraviolet (UV) light from mercury-free sources, the system can reduce total chlorine levels (including mono-, di-, and tri-chloramine and free chlorine) from the maximum 4.0 mg/L found in US tap water to below 0.1 mg/L, meeting the stringent requirements for home dialysis water. The approach addresses the limitations of conventional chlorine treatment methods by eliminating the need for chemical additives and reducing maintenance demands, making it well-suited for residential, healthcare, and small-scale water treatment applications.

The core innovation lies in coupling mercury-free UV sources—specifically excilamps and wavelength-tunable light-emitting diodes (LEDs)—with side-emitting optical fibers (SEOFs). This combination dramatically expands the effective area of UV irradiation in compact installations, enabling efficient treatment within the spatial constraints typical of point-of-use and home water systems.

Technical specifications

Key features:

• Multi-wavelength UV emission targets the distinct absorbance peaks of individual chlorine species across the UV spectrum, maximizing photolysis efficiency
• Mercury-free UV sources (excilamps and LEDs) eliminate the environmental and disposal concerns associated with conventional mercury lamps
• Side-emitting optical fibers increase the active UV irradiation area from a single LED source by up to 600 times
• Broad-spectrum UV output provides simultaneous microbial disinfection and advanced oxidation of organic contaminants
• Resilience to variable pH and water quality conditions, including both chlorine and chloramine-treated source waters
• Chemical-free operation removes the need for ongoing reagent dosing and associated handling
• Low-maintenance design validated through continuous field operation without cleaning over a one-year period

The technology exploits the principle that quantum yield is proportional to absorbance. By emitting across multiple UV wavelengths matched to the absorbance maxima of different chlorine species, the system achieves comprehensive chlorine photolysis that remains effective as pH-driven speciation shifts occur. The SEOF delivery mechanism distributes UV energy uniformly through water volumes, overcoming the limited penetration area typical of point-source LED emitters.

Technology readiness level

The underlying components have been individually validated. The PearlAqua UV LED water treatment reactor from Aquisense has been evaluated over one year of continuous field operation at a rural water system, maintaining disinfection performance without maintenance or cleaning despite challenging conditions. SEOF technology has been demonstrated to expand UV irradiation area by 600 times from a single LED source. Optimal wavelengths for disinfection have been identified through absorbance analysis of target biochemicals.

The next phase involves a yearlong partnership with Aquisense and SEOF researchers at Arizona State University to test individual and combined UV wavelengths using LEDs and excilamps delivered through SEOFs. Validation activities will include optimizing chlorine treatment across various water matrices using mass spectrometry to quantify individual chlorine species, measuring disinfection efficacy through culture and molecular methods, characterizing disinfection byproducts, and assessing radical production using chemical probes. Funding will support laboratory testing, device development, and personnel to advance the integrated system toward commercial readiness.