UV-Advanced Reduction Processes (UV-ARP) are an advanced water treatment technology characterized by hydrated electron (eaq-)-based degradation of chemical contaminants. UV-ARP have been shown to be effective for treating several classes of hard-to-degrade contaminants, like oxyanions and per- and polyfluoroalkyl substances, especially those classes that are resistant to degradation by advanced oxidative water treatment technologies (e.g., UV-AOP). Although eaq--based UV-ARP have been studied for decades, comparing results between operating conditions (lamp source/power, eaq- sensitizer, etc.) is difficult, even for the same target contaminant. In addition, while the general principles of UV-ARP largely parallel UV-AOP, many important parameters needed for fully describing UV-ARP remain poorly characterized. Some important knowledge gaps include uncertainty in eaq- bimolecular rate constants with important target contaminants (e.g., per- and polyfluoroalkyl substances) and an uncertainty in the background scavenging capacity of eaq- by various water matrix components (e.g., dissolved organic matter). The objective of this review is to critically evaluate the factors influencing the effectiveness of UV-ARP for the eaq--based degradation of chemical contaminants in water. We provide a critical evaluation of the UV-ARP literature, identify the knowledge gaps and limitations for these technologies, and suggest paths forward for future research. The data compilation and perspectives provided in this review will assist the UV-ARP research community in future efforts towards optimizing UV-ARP systems, deciding which contaminant classes are most treatable by UV-ARP, modeling the eaq--based chemical destruction kinetics, and developing novel UV-ARP systems.

Critical review of UV-advanced reduction processes for the treatment of contaminants in water

ACS Spring 2022

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