Modelling and Mechanisms for the Production of Singlet Oxygen in Ideal Systems and Wastewater Effluent

Abstract

Trace organic compounds (TOrCs) in natural waters and wastewater effluents are concerning to both environmental health and water reuse. Although some TOrCs are known to attenuate through photolytic and biologic processes, others remain and may interact with the environment. Reactive oxygen species (ROS), like singlet oxygen (1O2), are naturally produced by some organic matter and may increase attenuation of some TOrCs. This study looks at the generation of 1O2 by indirect photolysis in an (i) ideal system, and (ii) treated municipal wastewater effluent. In an ideal system using methylene blue (MB) as the photosensitive 1O2 generating source, furfuryl alcohol (FFA) was used as a 1O2 probe and p-cresol (PC) as a target compound. The degradation of FFA and PC were predicted under a UVA lamp and solar light using the quantum yield of triplet formation of MB as a fitting parameter. An investigation into the requirements of 1O2 producing compounds was completed and a list of 19 photosensitive TOrCs detected in wastewater effluents and impacted streams was compiled with their quantum yields of 1O2 generation and detected levels. Analysis of the wavelength dependence of 1O2 generation was done with wastewater effluent collected from Agua Nueva Wastewater Reclamation Facility. The effluent was concentrated and used as the photosensitizer with FFA used as the 1O2 probe. The concentrated wastewater was exposed to 6 different light sources with relatively narrow irradiance ranges and the quantum efficiency of 1O2 generation was determined in those ranges. The effluent used showed no 1O2 production over 4 hours of exposure to wavelengths of light above 600 nm. The quantum efficiency of the effluent organic matter (EfOM) ranged from 0.00014 to 0.034 with the 380 nm light source having the highest 1O2 generation.