Tannic acid promotes the activation of persulfate with Fe(ii) for highly efficient trichloroethylene removal

Trichloroethylene (TCE) is an Environmental Protection Agency (EPA) priority pollutant that is difficult to be removed by some remediation methods. For instance, TCE removal using persulfate (PS) activated by ferrous iron (Fe(ii)) has been tested but is limited by the unstable Fe(ii) concentration and the initial pH of contaminated water samples. Here we reported a new TCE removal system, in which tannic acid (TA) promoted the activation of PS with Fe(ii) (TA-Fe(ii)-PS system). The effect of initial pH, temperature, and concentrations of PS, Fe(ii), TA, inorganic anions and humic acid on TCE removal was investigated. We found that the TA-Fe(ii)-PS system with 80 mg L^-1 of TA, 1.5 mM of Fe(ii) and 15 mM of PS yielded about 96.2-99.1% TCE removal in the pH range of 1.5-11.0. Radical quenching experiments were performed to identify active species. Results showed that SO₄^˙- and ^˙OH were primarily responsible for TCE removal in the TA-Fe(ii)-PS system. In the presence of TA, the Fe-TA chelation and the reduction of TA could regulate Fe(ii) concentration and activate persulfate for continuously releasing reactive species under alkaline conditions. Based on the excellent removal performance for TCE, the TA-Fe(ii)-PS system becomes a promising candidate for controlling TCE in groundwater.