Is Perchlorate Degradation in a Zero-Valent Iron Barrier Biotic?

摘要

In 2006 a pilot-scale Dual Wall Permeable Reactive Barrier System (PRB) was installed downgradient of TCE and Perchlorate contaminant source areas. The PRB system was designed to treat TCE via an abiotic zero-valent iron (ZVI) treatment zone and perchlorate via a biotic treatment zone enhanced with organic material (molasses). Previous lab scale studies had shown the ZVI barrier alone would not reduce perchlorate levels. Field performance data showed nearly complete reduction of TCE concentrations in the ZVI barrier from the time of the baseline sampling through the last sampling event recorded. Perchlorate reduction in the baseline sample showed the concentration halved within the ZVI, and then dropped by another approximately 80% two weeks later. Concentrations of perchlorate sampled in another well just downgradient of the ZVI portion of the barrier showed a similar trend, declining from a baseline value of ~1,200 ug/L to near non-detect two weeks post startup. The efficacy of ZVI in treating perchlorate was unexpected as the reduction of perchlorate with ZVI alone is possible but the chemical activation energy is high and not usually considered suitable for in situ remediation. However, microbial perchlorate respiration has been well documented in situ and was investigated as a possible mechanism for perchlorate degradation in the ZVI portion of the barrier.