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Title:The development of a pseudo-mechanistic model of solar irradiation-induced inactivation of viruses in wastewater and natural waters
Author(s):Holyoke, Linda
Advisor(s):Guest, Jeremy S.
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Virus removal
Sunlight disinfection
Abstract:Waste Stabilization Ponds (WSPs) are a good alternative for providing sanitation services to developing rural communities because although they require relatively large areas of land, they are relatively inexpensive to construct and maintain. Beyond removal of chemical contaminants, they are exposed to solar irradiation which can enable the inactivation of viruses that are hazardous to human health. However, this sunlight disinfection is an unintentional byproduct of traditional WSP design, and consequently virus concentrations are not always reduced to sufficient levels. With the aim of improving virus inactivation in waters under sunlight, researchers have performed experiments to understand the mechanism of inactivation. The ultimate engineering objective of these lines of research is to develop a deep enough understanding of solar irradiation-induced virus inactivation to design a system to reliably leverage this process. To achieve this, however, a predictive model is needed. There have been attempts at modeling a subset of mechanisms of virus inactivation in natural waters and wastewaters but none have addressed exogenous inactivation, which has been demonstrated to be a key contributor to inactivation. To address this critical gap, the objective of this thesis is to begin the development of such a model to predict exogenous inactivation based on irradiation conditions of the water and concentrations of known reactive species (RS) for the pathogens human rotavirus (HRV), bacteriophage MS2, and porcine rotavirus (PRV). Assembled here are data from eight recent experimental studies which have been used to both calibrate a simple model and elucidate the dependence of inactivation on irradiance wavelength. First, with one data set, the only available study of its kind, it was possible to determine the wavelength dependence of singlet oxygen, an RS for MS2, HRV, and PRV inactivation. A significantly higher efficiency of singlet oxygen production was observed when smaller wavelengths within the UVA region are absorbed (~2x increase from 400nm to 315nm). This suggests that any predictive model of virus inactivation must include quantitative distinctions of inactivation rate between wavelengths. Second, the correlations between key mechanism parameters between several studies were assessed. This analysis demonstrated that variability between water samples from one study to another are great enough that the use of only one parameter, such as the concentration of one RS type or total number of absorbed photons, is insufficient for a universal prediction method. In light of this observation, a simple model incorporating all known RS was established and calibrated for MS2. For this system, three coefficients were determined–one each for the RS singlet oxygen (1O), hydroxyl radical (OH), and triplet-excited dissolved organic matter (3DOM)–which indicate the relative contributions of each RS. The average coefficient values found were in the ratios of 1 : 163 : -190 (1O : OH : 3DOM). This may allude to the quenching effect of triplet-excited DOM on hydroxyl radical. The uncertainty in coefficients results in inactivation rate prediction uncertainty, but the latter must be weighed against the uncertainties in other environmental conditions. The variability in conditions also affecting inactivation such as cloud cover and temperature must be accounted for and ultimately included in a predictive model used for aiding WSP design and operation. More experiments measuring all involved parameters are warranted.
Issue Date:2014-09-16
Rights Information:Copyright 2014 Linda Nitta Holyoke
Date Available in IDEALS:2014-09-16
Date Deposited:2014-08

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