The effects of various amendments on the biostimulation of perchlorate reduction in laboratory microcosm and flowthrough soil columns

•Three amendments to biostimulate perchlorate reduction were investigated.•Experiments were conducted in microcosms and flowthrough biobarrier columns.•Water and soil used were from an actual contaminated site.•Two commercial amendments proved effective, a compost/mulch mixture showed mixed results.•Overall, the results should support better site remediation decisions.

Perchlorate (ClO4-) is a contaminant of concern in groundwater and drinking water. In the presence of a suitable electron donor, perchlorate can be reduced to non-toxic chloride via either biotic or abiotic mechanisms. The objective of this study was to evaluate a variety of amendments (Emulsified Oil Substrate (EOS®598), EHC® and a compost/mulch mixture) and supplemental nutrients to stimulate in situ perchlorate bioremediation. Both laboratory microcosm and column experiments were conducted with groundwater from a contaminated site that had an initial perchlorate concentration of about 500 μg/L. Complete perchlorate removal was observed within 5–12 days in all the microcosms. The addition of 1 g/L (NH4)2HPO4 as nutrient increased the reduction rate of perchlorate in EOS and compost/mulch microcosms, but had no effect in the EHC amended microcosms. Two different flowthrough experiments were conducted. Phase 1 used two parallel columns packed with EOS-amended compost/mulch/gravel media and EHC-amended compost/mulch/gravel media, while in Phase 2, a series of varying length columns ranging from 0.15 m to 0.60 m were packed with EOS-amended soil and EHC-amended soil. No perchlorate was detected in the effluent of both EOS- and EHC-amended compost/mulch/gravel columns after 20 days. In Phase 2, no significant treatment difference was observed between the EOS- and EHC-amended soil columns. Complete perchlorate removal was observed after 6 to 11 days in all different length columns when they were operated at a hydraulic loading rate of 0.15 m3/m2-d. Perchlorate removal was completely lost in all the columns when the hydraulic loading rate was increased to 0.60 m3/m2-d. Nitrate competed with perchlorate for electrons, and was a preferred acceptor over perchlorate. Overall, based on the results of this study, the two commercial amendments can be considered as effective means for perchlorate bioremediation, although EHC had a shorter period of effectiveness.