Persistence of peroxydisulfate in aquifer material

In the last ten years the peroxydisulfate (PDS) application as oxidant for in-situ chemical oxidation (ISCO) technology became popular for remediation of contaminated soil and groundwater. Due to its high oxidation potential, PDS has a high capacity to degrade a wide variety of contaminants. However, due to its low use, a lot of information are not available about stability, persistence, and transport. The objective of this study was to identify the stability of unactivated PDS in presence of two soils from Czech Republic and a sea sand. Degradation rate coefficients and half-life were analyzed and the dependence on total organic carbon (TOC) and inorganic elements content, such as Fe and Mn, was studied. A series of batch and column experiments were performed to estimate the changes in PDS concentration over time. Batch experiments were conducted in triplicates in a system containing 100 g of solids at 1 or 20 g/L of PDS. Column experiments were performed injecting PDS with constant flowrate (5 mL/min) at high concentration (20 g/L) into the columns containing natural soil or sea sand. PDS changes were analyzed studying breakthrough curves (temporal evolution of PDS concentration in the effluent). The decomposition of PDS followed the first-order rate law for all aquifer materials investigated and was strongly related to TOC and Fe content. For the soil with higher TOC content, the decomposition was faster with an exponential decay over time. On the other hand, in absence of TOC content, there was no evident reaction with PDS. Column experiments gave information about decomposition and transport of PDS showing that for the soil with high TOC content there was an evident reactivity with PDS. The soil with no TOC and Fe content, quickly reached the influent concentration showing an absence of reaction with PDS. The results showed that TOC and Fe content played an important role in PDS loss and the study of these properties were able to give information about persistence and stability of PDS.