# Activation of Persulfate for Groundwater Remediation:
###### Abstract  
Persulfate-based in situ chemical oxidation (ISCO) has been increasingly used for the remediation of contaminated groundwater and soil. In recent years, there have been numerous studies in the literature on all aspects of the activation of persulfate for contaminant removal at the laboratory scale, including the ways and mechanisms for the activation, the pathways of contaminant degradation, the factors associated with the activation performance, the methods characterizing the processes, etc. In contrast, studies in the literature on the practical use of the activated persulfate at the field scale are fewer, and at the same time have not been reviewed in an organized way. This review was initiated to summarize on the current research on the applications of activated persulfate for actual site remediation, and to extract the knowledge necessary for the formation of applicable technologies. The remediation efficiency and mechanism of activated persulfates by heat, alkaline, metal-based, and electrokinetic activated technologies are described. The major factors including pH, the persistence of persulfate, and the radius of influence and soil property during ISCO remediation applications were presented and discussed. Finally, the rebound process and impact towards microbial communities after in-situ chemical oxidation on site application were discussed. persulfate activation; in situ chemical oxidation; degradation of organic pollutants; groundwater remediation +
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persulfate is effective for recalcitrant compounds for which most other oxidants (such as permanganate) are not, which enables it to degrade a broad range of organic contaminants, such as petroleum hydrocarbons [14; 15], chlorinated ethylene [16], chlorinated alkanes [12], dioxane [17; 18], methyl tert-butyl ether (MTBE) [19; 20], polycyclic aromatic hydrocarbons (PAHs) [21; 22; 23], and per- and polyfluoroalkyl substances (PFAS) [24; 25]. Although persulfate (S2 Os2-) is an oxidant with a redox potential of 2.01 V, its reaction with many refractory contaminants is slow and activation is usually required for optimal performance [26]. In general, activation of persulfate means production of sulfate radical (SO4-), a much stronger oxidant species with a redox potential of 2.5-3.1 V depending on the solution conditions [27]. The common approaches for activating persulfate are the use of bases [28], UV irradiation [29], heat [29], and transition metal and metal oxides [30; 31]. Some novel approaches include the use of phenols [32], quinones [33], naturally occurring metal oxides [34; 35], and iron filings [18] as activators. For the successful application of persulfate to degrade contaminates, some crucial points, such as the activation of persulfate, the dosage of persulfate, the physicochemical properties of soil, and the monitoring of soil and groundwater during and after remediation should be considered. Because the application of this method is mainly through activating persulfate to produce a sulfate radical to degrade pollutants, a mechanistic understanding of the activation of persulfate by different methods, e.g., the use of bases, heat and transition metal and metal oxides, is of great significance. Some parameters, including persulfate dosage, transport distance of persulfate in soil, and pH of groundwater and soil, determine the remediation efficiency. Indeed, there are some review studies about the activation mechanism and application of persulfate and influencing factors at the laboratory scale [4; 6; 36; 37; 38; 39; 40; 41; 42; 43; 44]. To the best of our knowledge, few reviews have focused specifically on applications of persulfate at pilot and field scales [44]. [PERSON] et al. (2010) discussed the mechanism of persulfate for remediation of contaminated soils and groundwater, activation methods including heat, iron, and alkaline activation, and in-situ oxidation effects [44]. However, some recent achievements in the laboratory and the development of on-site applications have not been included.