Remediating phenol-contaminated groundwater and aquifer using persulfate oxidation

A chemical spill in Chachoengsao province, Thailand resulted in a phenol-contaminated aquifer. Our objective was to remediate the phenol-contaminated groundwater and aquifer using oxidation with persulfate (PS). Groundwater and aquifer collected near a source zone were characterized and used in the experiments. The experimental design was set up under the criteria of specific sites and contaminants. To optimize efficacy, various experimental variables were tested: initial persulfate (PS) and phenol concentrations, pH, transition metals as persulfate activators, and the concentration ratios of PS to Fe²⁺. The phenol degradation rates enhanced when the pH was increased from 3 to 7 but then continually decreased as the pH was increased from 7 to 9. Five transition metal (Fe²⁺, Cu²⁺, Zn²⁺, Pb²⁺, and Cd²⁺) were tested as PS activators. By using equivalent molar concen-trations, we found the rate of phenol degradation was highest when PS was activated by Fe²⁺. By using a 500:5 PS to Fe²⁺ ratio, phenol removal efficiency increased almost three-fold over a 500:1 PS to Fe²⁺ ratio (k_obs = 0.35 h^–1 vs. k_obs = 0.12 h^–1). Using a statistical-based response surface method-ology, we found that the optimum conditions for treating phenol-contaminated groundwater were 522.40 mg PS L^–1 with 4.85 mg Fe²⁺ L^–1 at pH 6.99. The use of activated persulfate to remove phenol during miscible displacement was also investigated. Column leaching experiments were per-formed where persulfate was injected into an aquifer column containing 1% zerovalent iron (w/w) as an activator. The results showed that after displacing three pore volumes, phenol concentrations decreased 82%. Using activated persulfate also increased the percentage of phenol oxidized during transport by 20%. These results confirmed the use of activated persulfate for the removal of phenol from contaminated groundwater and aquifer.