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Title:Photochemical processes in engineered aquatic systems for remediation of per- and polyfluoroalkyl substances and algae cultivation
Author(s):Tenorio, Raul
Director of Research:Strathmann, Timothy J; Guest, Jeremy S
Doctoral Committee Chair(s):Strathmann, Timothy J; Guest, Jeremy S
Doctoral Committee Member(s):Nguyen, Thanh H; Higgins, Christopher P
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):water treatment
groundwater remediation
hydrated electron
per- and polyfluoroalkyl substances
algal photochemistry
Abstract:Photochemical processes drive many important reactions in environmental engineering applications, ranging from engineered treatment processes (e.g., micropollutant removal) to natural biogeochemical processes (e.g., nutrient cycling). This thesis investigates (1) the application of a UV-sulfite photochemical treatment process for per- and polyfluoroalkyl substances (PFASs) destruction, and (2) the generation of photochemically produced reactive species in algal cultivation systems where cells excrete light-absorbing extracellular substances. The production of highly reductive hydrated electrons (eaq−; NHE = −2.9 V) in UV-sulfite treatment has shown promise in the destruction of PFASs. PFASs are a component in aqueous film-forming foam (AFFF) used in fire-training activities and have caused widespread contamination across the U.S. While recent studies have shown promise in UV-sulfite treatment of individual PFASs, little is known of treatment in PFAS mixtures found in AFFF-impacted waters. This thesis investigates the application of UV-sulfite treatment in the complex PFAS mixtures present in dilute solutions of AFFF concentrate and AFFF-impacted groundwaters. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) methods allowed for simultaneous analysis of a wide array of PFASs, including compounds for which no reference standards are available, and yielded valuable kinetic information used to establish structure-reactivity relationships. Results show that reactivity varies widely among the 15 PFASs detected by targeted analysis. While some structures, (e.g., long-chain perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs)) were readily degraded, other structures (e.g., short-chain PFSAs and fluorotelomer sulfonic acids (FTSs)) were more recalcitrant. Furthermore, results show that PFSAs, PFCAs, and FTSs can form as transient intermediates or unreactive end-products by reactions between eaq− and precursors in AFFF. Seventy-three additional PFASs were detected by suspect screening analysis. Among identified structures, sulfonamide precursors and precursors of FTSs and fluorotelomer carboxylic acids (FTCAs) were the most reactive, indicating that these may be the sources of PFSA, PFCA, and FTS generation observed early on in UV-sulfite reactions that was reported previously. While most PFSAs showed few reactivity differences among groundwaters, PFSA reactivity was enhanced in groundwaters compared to single-solute experiments conducted in laboratory buffer solutions at similar pH conditions. In contrast, PFCA reactivity varied in different groundwaters and decreased in reactivity compared to single-solute experiments. Conclusions from this work help develop UV-sulfite into a viable treatment technology and provide insight into treatment in environmentally relevant remediation scenarios. This thesis also investigates reactive species production in algal cultivation systems where previous research has primarily focused on biofuel production and nutrient recovery. Extracellular organic matter (EOM) and growth medium in the extracellular matrix of an algal cultivation system photoproduced excited triplet state dissolved organic matter (3DOM*), hydroxyl radicals (HO•), and singlet oxygen (1O2). Comparisons with Suwannee River natural organic matter (SRNOM) showed that EOM solutions exhibited lower light absorption and reactive species production than SRNOM solutions per mg-C·L−1. However, 3DOM* quantum yield coefficients, HO• apparent quantum yields, and 1O2 apparent quantum yields in EOM solutions could be greater than or comparable to SRNOM solutions depending on algal growth phase. EOM solutions also photoproduced reactive species at levels comparable to natural waters. Conclusions from this work reveal potential opportunities for developing versatile algal technologies that combine contaminant abatement, bioenergy production, and nutrient recovery.
Issue Date:2020-11-09
Rights Information:Copyright 2020 Raul Tenorio
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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