Coupling of polyhydroxybutyrate (PHB) and zero valent iron (ZVI) for enhanced treatment of chlorinated ethanes in permeable reactive barriers (PRBs)

In this work, the use of polyhydroxybutyrate (PHB) as a feasible carbon source in a permeable reactive barrier (PRB) was investigated as a strategy for enhancing the performance of zero valent iron ZVI towards chlorinated ethanes, increasing iron reactivity and longevity and enhancing biological reductive processes. Results concerning PHB fermentability under the conditions created by the ZVI reactive zone are presented. Column experiments were performed to verify whether PHB can be anaerobically fermented with the production of volatile fatty acids (VFAs) and H2, which in turn can be used as electron donors for downstream biological reductive dechlorination. Acetate and butyrate were detected in the effluent of the Fe/PHB-column at concentrations as high as 2500 and 700 mg/L, respectively, confirming that microbially induced PHB hydrolysis and fermentation was readily established without the need for an external inoculum. The formation of high VFA concentrations significantly lowered the pH of the Fe/PHB-column liquid phase with respect to that observed in the presence of only ZVI. The combined effect of the acidic conditions and the dissolved VFA significantly enhanced ZVI reactivity and longevity, likely due to the prevention of passivation of the iron surface by Fe(II) and Fe(III) (hydro)oxide precipitation. As a consequence, TeCA, used as a target parent contaminant, and its byproduct degradation rates were significantly increased, as was the durability of the reactive material.

► PHB could be effectively used as a feasible releasing electron donor in ZVI-PRB.
► PHB hydrolysis and fermentation readily established within ZVI reactive bed.
► High VFA concentration and low pH significantly enhances ZVI reactivity.
► Combined use of ZVI and PHB could extend durability of ZVI in full scale PRBs.