Theme: 01. Remediation Technology Innovations

Topic Area: 01c. Permeable Reactive Barriers: Best Practices and Lessons Learned

Formatted Title:

A Reactive Multibarrier for the Abatement of Chlorinated Compounds: From Laboratory Tests to Pilot Installation

Background/Objectives:

In this study we present the design steps of an in situ reactive multibarrier for the abatement of chlorinated solvents and metals from the laboratory tests to the pilot installation. The impacted area falls into one of the 42 Italian contaminated sites of national importance (Sito di interesse nazionale – SIN). The groundwater in the site is contaminated by chlorinated organic compounds and metals, such as 1,2-dichloroethane (1,2-DCA), tetrachlorethylene (PCE), trichloroethylene (TCE), cis-1,2-dichloroethylene (1,2-DCE), vinyl chloride (VC), trichloromethane (TCM) and arsenic. The conceptual model of the area indicates the presence of a plume of dissolved contamination characterized by a width of about 150 m and an extension of over 300 m along the flow direction. Among the contaminants, 1,2-DCA is the most critical since it is present in high concentrations (tens of mg/L in groundwater) and is highly recalcitrant to treatments involving reductive dehalogenation, including both abiotic and biological approaches.

The groundwater remediation plan involves the installation of a reactive multibarrier composed of: i) an impermeable wall to intercept the plume and prevent the downstream migration of the contaminants; ii) a pumping system installed upstream of the barrier for groundwater extraction; iii) a multistage treatment system for the removal of pollutants; iv) an infiltration system installed downstream of the barrier to release the treated water back into the aquifer. The multistage treatment system is in turn composed of two reactive filters installed in series and respectively filled with: i) millimetric zerovalent iron (ZVI) for the removal of arsenic and chlorinated aliphatic hydrocarbons that can be treated by abiotic reductive dehalogenation; ii) granular activated carbon (GAC) for the removal by adsorption of 1,2-DCA (non-degradable with ZVI) and residual organic contaminants.

Approach/Activities:

In this study, groundwater treatability tests were carried out in the laboratory to optimize the site-specific design and sizing of the reactive filters. First, batch tests were performed to compare different types of ZVI and GAC and to select the most effective reactive materials. Then, column tests were carried out to verify the effectiveness of the treatment chain in flow conditions and to determine the reactive material longevity. Based on the information obtained from laboratory tests, a pilot scale multibarrier was installed on-site to verify the performance of the filtration chain in field conditions. The pilot system, which included only the extraction and filtration sections (no impermeable wall and infiltration system), was also equipped with sensors to monitor key parameters (pH, ORP, pressure) of the treatment chain.

Results/Lessons Learned:

The test results confirmed the effectiveness of the multibarrier under the tested conditions. The ZVI filter ensured a 99.9% removal of many chlorinated solvents, such as PCE, TCE and TCM, and a complete abatement of the arsenic, while a 60% degradation was observed for 1,2-DCE and VC. As expected, 1,2-DCA proved to be recalcitrant to treatment with ZVI. Full removal of all residual contaminants, including 1,2-DCA, was instead observed upon GAC filtration. Overall, the treated groundwater at column outlet was found to be fully compliant with the concentration limits set for water release into the aquifer. Mathematical models were finally applied to interpret the experimental results and obtain quantitative parameters useful to design the large-scale multibarrier, i.e., the kinetic constants of contaminant removal in the ZVI filter, the expected longevity of the reactive materials, as well as the volumes of reagent necessary to meet the target concentrations for each contaminant. Specifically, a multicomponent adsorption model was used to interpret and design the GAC filtration step. The preliminary results of the pilot test, which is still ongoing, confirmed the potentiality of the reactive multibarrier to effectively remediate groundwater in site-specific conditions.

Tiziana Tosco

Affiliation

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(Group 2, Poster Board #216) A Reactive Multibarrier for the Abatement of Chlorinated Compounds: From Laboratory Tests to Pilot Installation