UV/Sodium percarbonate for bisphenol A treatment in water: Impact of water quality parameters on the formation of reactive radicals.

Reported herein is an investigation of the impact of water quality parameters on the formation of carbonate radical anion (CO3•-) and hydroxyl radical (HO•) in UV/sodium percarbonate (UV/SPC) system versus in UV/hydrogen peroxide (UV/H2O2) system for bisphenol A (BPA) degradation in water. Pathways of CO3•- oxidation of BPA were proposed in this study based on the evolution of direct transformation products of BPA. Observed in this study, the degradation of BPA in the UV/SPC system was slower than that in the UV/H2O2 system in the secondary effluents collected from a local wastewater treatment plant due to the significant impact of coexisting constituents in the matrices on the former system. Single water quality parameter (e.g., solution pH, common anion, or natural organic matter) affected radical formations and BPA degradation in the UV/SPC system in a way similar to that in the UV/H2O2 system. Namely, the rise of solution pH decreased the steady state concentration of HO• resulting in a decrease in the observed pseudo first-order rate constant of BPA (kobs). Chloride anion and sulfate anion played a negligible role over the examined concentrations; nitrate anion slightly suppressed the reaction at the concentration of 20 mM; bicarbonate anion decreased the steady state concentrations of both CO3•- and HO• exerting significant inhibition on BPA degradation. Different extents of HO• scavenging were observed for different types of natural organic matter in the order of fulvic acid > mixed NOM > humic acid. However, the impact was generally less pronounced on BPA degradation in the UV/SPC system than that in the UV/H2O2 system due to the existence of CO3•-. The results of this study provide new insights into the mechanism of CO3•- based oxidation and new scientific information regarding the impact of water quality parameters on BPA degradation in the sytems of UV/SPC and UV/H2O2 from the aspect of reactive radical formation, which have reference value for UV/SPC application in wastewater treatment.

An overview on surfactants as pollutants of concern: Occurrence, impacts and persulfate-based remediation technologies.

Surfactants are molecules that reduce interfacial energy and increase solubility of other pollutants in water. These properties make them suitable for various domestic and industrial applications, soil remediation, pesticide formulation, among others. The increase in their use and the lack of strict regulations regarding their disposal and management is a matter of concern and requires more attention since the release and distribution of these compounds into the environment can modify important water quality parameters. As a result of these changes, different toxicological effects to aquatic organisms are discussed and exposed herein. On this basis, we provide an overview of the classes of surfactants, as well as their occurrence in different aqueous matrices. In addition, existing regulations around the world regarding their concentration limit for different environments are discussed. Current research focuses on the application of conventional treatments, such as biological treatments; notwithstanding, more toxic and bioaccumulative products can be generated. Advanced Oxidation Processes are promising alternatives and have also been widely applied for the removal of surfactants. This study provides, for the first time, an overview of the application of persulfate-based processes for surfactants degradation based on recent literature findings, as well as the various factors related to the activation of the persulfate anions. This review also highlights the challenges and opportunities for future research to overcome the obstacles to the practical application of this process.

Dodecylpyridinium chloride removal by persulfate activation using UVA radiation or temperature: experimental design and kinetic modeling.

The degradation of dodecylpyridinium chloride (DPC) by SO4•- and HO• radicals, generated by UVA and thermal-activated persulfate (PS) was investigated. Temperatures of 30-50°C were used for the heat activation of PS. In the case of UVA/PS, the effects of [PS]0 and specific photon emission rate (EP,0) were studied through a Doehlert design coupled with statistical analysis and response surface methodology. The results showed high DPC removal (99.8%) and pseudo-first-order degradation rate (kobs = 0.0971 min-1) for [DPC]0 = 4.60 ± 0.11 mg L-1, [PS]0 = 7.75 mmol L-1, and EP,0 = 0.437 µmol photons L-1 s-1, with a major role of SO4•- radicals in comparison with HO•. The specific DPC degradation rate found under these conditions was higher than that observed for thermal activation at 50°C and [PS]0 = 5.5 mmol L-1 (kobs = 0.0712 min-1) over the same time, although complete DPC removal was also achieved in the latter. The positive effect of EP,0 on DPC degradation by the UVA/PS process depends on PS concentrations, with kobs values increasing linearly with [PS]0 in the range 7.75-10 mmol L-1, whereas lower EP,0 values can be compensated by increasing [PS]0 up to about 10 mmol L-1, without significant scavenging. The second-order rate constants of DPC with HO• and SO4•-, estimated by comprehensive kinetic modeling, were 8.26 × 109 and 4.44 × 109 L mol-1 s-1, respectively. Furthermore, higher [DPC]0 would negatively affect the DPC degradation rate by the UVA/PS process, while 62% DPC removal was obtained in WWTP water, which can be considered good given the complexity of the real matrix. Finally, our results shed light on the possibility of using available UVA radiation (4.5%) in solar irradiance on the Earth's surface, making this treatment process more sustainable and cost-effective.