Physical and Analytical Chemistry Seminar

Lecturer: Guy Moldovan

10-10 Sep 2019

Location: Faculty Seminar Room

An Optical Method for Monitoring of Disinfectants in Water

Water analysis presents a complex challenge, whether it be drinking water, sea water or wastewater. One aspect of water quality is its microbial levels, which is especially important to control due to the associated health risks. One of the most common and effective disinfectants used to maintain safe bacterial levels is hypochlorous acid. Nevertheless, this disinfectant suffers from photochemical decomposition when exposed to UV light, limiting its use to indoor waters. Thus, cyanuric acid is often added in order to stabilize this disinfectant. Due to a series of chemical reactions of the disinfectant with cyanuric acid, its concentration decreases and many chlorocyanurates are formed. These species also absorb light, thus interfering with the spectral monitoring of the disinfectant itself. Commonly used methods for quantification of the disinfectant and cyanuric acid lack the ability to differentiate between the disinfectant and its various chlorocyanurate derivatives. This may result in false readings, low accuracy and may require utilization of time consuming lab analyses. Our goal was to develop an on-line optical method for monitoring the disinfectant levels in waters, where cyanuric acid is used as a stabilizer, and which can be used for field applications. We utilized the UV photo-decomposition kinetics for gaining analytical information. This was based on a simplified kinetic model. We also developed several unique spectroscopic designs in order to allow for better sensitivity. Besides the full spectral approach, we developed a simple low-cost setup based on a single wavelength measurement, and evaluated its analytical performance.