Remediation of MTBE Contaminated Water and Soil

As the number of leaking underground fuel tank sites with MTBE contamination continues to grow, there is a need to develop cost-effective solutions for treatment of soil and water contamination. MTBE poses special challenges due to its physicochemical properties, in particular high solubility and low Henry’s constant, low affinity for sorption, and very slow rate of microbial degradation. Advanced oxidation processes tend to generate undesirable byproducts. Based on laboratory studies with hollow fiber membranes (HFM), a field-scale unit was constructed and tested at a number of sites, to determine the effectiveness of this technology in dealing with MTBE contamination. In addition, to treat the soil contamination, the HFM unit was coupled with a Spray Aeration Vapor Extraction (SAVE) unit, which is based on an internal combustion engine. The engine provides the means to treat soil vapors, as well as organic vapors from the spray aeration and HFM units. The overall treatment objectives of 5 μg/L for MTBE and 1 μg/L for benzene were achieved with a treatment train consisting of an ion exchange unit, a spray aeration system, a hollow fiber membrane module and two granular activated carbon units, for flowrates ranging from 3.8 to 30 L/min (1 to 8 gal/min). The ion exchange unit served to reduce water hardness and avoid scaling in the subsequent treatment units, extending the run-time of the entire system. Overall removal efficiencies for the spray aeration system and hollow fiber membrane module ranged from 85 to over 99%. High removal efficiencies (> 97%) were obtained at elevated water temperatures (54 C) or lower flowrates (up to 11 L/min). The GAC units were used only to polish the effluent and meet the discharge requirements. Soil, water and gas phases are treated with this system. Cost estimates are provided for similar treatment processes, for water flowrates up to 38 L/min (10 gal/min).