Synergistic action of ferrate and biochar in the removal of trichloroethylene from water: Little biochar addition, large ferrate activity improvement

Ferrate (Fe(VI)) is strongly considered an efficient green oxidant for degrading organic pollutants in groundwater. However, overdosage is often used to achieve the desired efficiency, resulting in adverse effects on the groundwater quality and the ecological environment and high costs. This study aimed to enhance the removal of trichloroethylene (TCE) using Fe(VI) by investigating the synergistic action of a ferrate-biochar system. 1 h into the reaction, the TCE degradation rate had increased from 18.7% to 96.0% and the K2FeO4 concentration had increased from 1 mM to 25 mM. The pH strongly influenced the TCE degradation by K2FeO4 by affecting the stability, species, and consequent oxidation capacity of K2FeO4. Co-existing metal cations in the solution could enhance the K2FeO4 self-decay by facilitating the electron transfer process. Biochar addition significantly enhanced TCE removal by K2FeO4 (up to 4.4 times) compared with the combined removal via individual oxidation and adsorption systems. Significant enhancement comparable to that of a high 16 mM Fe(VI) dosage was obtained with 666 mg/L biochar and 5 mM Fe(VI). The enhancement mechanisms by which biochar addition enhanced the TCE removal by K2FeO4 included the oxidation process by prior to TCE adsorption onto biochar, an enhanced electron transfer of Fe(VI) reduction by the biochar functional group, and an enhanced adsorption capacity of biochar owing to its peroxidation by Fe(VI). Thus, compared to individual and excessive chemical oxidation, the ferrate-biochar composite system provides a promising strategy for improving the TCE removal efficiency with lower oxidant consumption and less negative ecological impacts.