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TREATMENT OF CONTAMINANTS OF EMERGING CONCERN BY ADVANCED OXIDATION PROCESSES AND REVERSE OSMOSIS
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2022
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Environmental Engineering
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http://dx.doi.org/10.34944/dspace/7977
Abstract
The discussion about contaminants of emerging concern (CECs) is now more prevalent than ever with the ever-increasing topic of non-potable and potable water reuse, especially with direct potable reuse. In the past and today, discharging CECs into an environmental buffer without complete removal is common practice. The Southern and Southwestern United States have been experiencing megadroughts and water shortages and have seen one of the biggest increases in population growth, and these factors put an additional strain on the water demand. Coupled with large, urbanized areas with increased life expectancy (aging population) only contributes to the rise of CECs in the wastewater treatment plants (WWTP) and, subsequently, the surface waters. The CECs previously discharged into the environment can no longer be ignored.This first part of this dissertation was carried out to increase our understanding of the concentration, distribution, occurrence, and potential risk of personal care products (PPCPs) by sampling large and small tributaries of the Delaware River in Pennsylvania. PPCPs are one of the largest categories of CECs and require further investigation. Working from a previous multiyear study conducted by the Delaware River Basin Commission (DRBC) on the main stem of the Delaware River, fifteen compounds were selected based on their high frequency of detection. Ten sampling sites were chosen on tributaries receiving numerous municipal and industrial discharges. Sampling locations were above and below potential source discharges. Sampling was conducted in three different seasons to account for seasonal differences in CECs loadings. The measured environmental concentrations of the target compounds present an insight into the urban and industrial impacts on subwatershed receiving waters. An index for levels of concern (LOC) was applied to the sample locations by comparing measured environmental concentrations, existing target compound water quality criteria, predicted no effects levels, and developing a concern summary variable. All the PPCPs were detected at high frequencies. Triclocarban and diphenhydramine demonstrated to be compounds of high relative risk (RR) to the aquatic life of the Pennsylvania tributaries to the Delaware River. Metformin was labeled low concern but had the highest environmental concentrations and continual presence due to high loading.
The second part of the work focused on an unorthodox approach to treating CECs. Advanced oxidation processes (AOPs), specifically ultraviolet (UV) light and hydrogen peroxide (UV/peroxide), were deployed as a pretreatment to the reverse osmosis (RO) feed. The use of AOPs with RO is commonly used in the treatment (polishing) of the permeate and the treatment of the concentrate. As per California’s State Water Resources Control Board, one of the regulatory leaders in water reuse in the US, 1,4-dioxane was utilized as a benchmark to estimate the water reuse processes' efficiency with a minimum 0.5 log10 (69%) reduction. UV/peroxide showed to be an effective AOP in removing multiple CECs in a simulated RO feed. Based on the electric energy per order of removal (EE/O), pretreatment is four-fold more efficient than posttreatment. AdOx™ modeling software was utilized to estimate the treatment kinetics of the feed water and the concentrate. Pretreatment showed to be a viable, more efficient option for treating the CECs with RO compared to the post-treatment of the concentrate and the permeate.
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