Reinvestigation on the Mechanism for Algae Inactivation by the Ultraviolet/Peracetic Acid Process: Role of Reactive Species and Performance in Natural Water

Abstract

This study provided an in-depth understanding of enhanced algae inactivation by combining ultraviolet and peracetic acid (UV/PAA) and selecting Microcystis aeruginosa as the target algae species. The electron paramagnetic resonance (EPR) tests and scavenging experiments provided direct evidence on the formed reactive species (RSs) and indicated the dominant role of RSs including singlet oxygen (1O2) and hydroxyl (HO•) and organic (RO•) radicals in algae inactivation. Based on the algae inactivation kinetic model and the determined steady-state concentration of RSs, the contribution of RSs was quantitatively assessed with the second-order rate constants for the inactivation of algae by HO•, RO•, and 1O2 of 2.67 × 109, 3.44 × 1010, and 1.72 × 109 M–1 s–1, respectively. Afterward, the coexisting bi/carbonate, acting as a shuttle, that promotes the transformation from HO• to RO• was evidenced to account for the better performance of the UV/PAA system in algae inactivation under the natural water background. Subsequently, along with the evaluation of the UV/PAA preoxidation to modify coagulation–sedimentation, the possible application of the UV/PAA process for algae removal was advanced.

Overlooked Role of Coexistent Hydrogen Peroxide in Activated Peracetic Acid by Cu(II) for Enhanced Oxidation of Organic Contaminants

“…Nevertheless, PAA alone could only directly degrade certain organic contaminants with electron-rich structures (e.g., sulfur moiety, aromatic ring, and CC bond) . Up to now, a number of activation strategies have been proposed to enhance the oxidative performance of PAA, such as energy input (e.g., ultraviolet, , heat, electrochemistry, microwave, and ultrasound), metal catalysts (e.g., homogeneous − and heterogeneous − transition metals), carbon materials, , and anionic catalysts (e.g., phosphate, bromide, , iodine, , chloride, and nitrite), etc.…”

Identification of Superoxide Contribution through the Quenching Method and Model System

“…The quenching method is commonly used to assess the maximum contribution of a specified reactive species by adding an excessive amount of quencher to induce inhibition. This method has gained popularity due to its simplicity and convenience, finding successful applications in various fields. − However, our previous research on the quenching of singlet oxygen ( 1 O 2 ) has revealed that multiple relationships exist between the quenching effect and the contribution of reactive species, rather than simple inhibition indicating contribution . Additionally, other studies also pointed out that quenchers may alter the production conditions or mechanisms of reactive species, , potentially leading to evaluation errors.…”