Lab-scale tests and numerical simulations for in situ treatment of polluted groundwater.

Methyl tert-butyl ether (MTBE) is used at significant percentages as an additive of unleaded gasoline. The physical-chemical properties of the substance (water solubility, soil organic carbon-water partition coefficient) cause high mobility and high concentrations in groundwater. Laboratory scale batch and column tests and mathematical modeling were performed to study the feasibility of a biobarrier (BB), that is an in situ permeable biological barrier with or without inoculation, for the remediation of MTBE and other gasoline-derived pollutants (benzene, toluene, ethylbenzene, o-xylene and m+p-xylenes, BTEXs) polluted groundwater and to estimate kinetic constants. The experimental results showed simultaneous biodegradation of MTBE and BTEXs, with similar removals in the uninoculated and the inoculated systems. Ranges for the first order kinetic removal were obtained for MTBE ((0.18±0.02)/(0.28±0.11d(-1))), B ((0.39±0.12)/(0.56±0.12d(-1))), T ((0.51±0.03)/(0.78±0.15d(-1))), E ((0.46±0.18)/(1.57±0.21d(-1))), o-X ((0.24±0.08)/(0.64±0.09d(-1))) and m+p-X ((0.20±0.04)/(1.21±0.04d(-1))). The results of the laboratory tests allowed to improve mathematical modeling in order to design a full-scale BB at a gasoline-contaminated site.

Biobarriers for groundwater treatment: a review.

Biobarriers (BBs) are a new type of in situ technology for the remediation of contaminated groundwater. In recent years, this remediation technique has been more and more used in place of traditional Pump & Treat systems or other in situ technologies both in the USA and Europe. This work reviews the main experiences of BBs. The literature contains reports about tests and application at different scales (laboratory, pilot and full scale), which have been analyzed according to the aim of the study, the operative conditions adopted, the filling material, the inoculation procedure, the electron acceptor and the nutrient delivery systems. Operative conditions were extremely varied. Lab scale experiments pointed out good results in terms of pollutant removal efficiency. Pilot scale tests and full-scale applications confirmed the results obtained at lab scale, but also pointed out the importance of design for a proficient remediation system. The experiences underlined some possible critical issues: (a) the filling material must ensure proper hydraulic properties, but it also must be capable of keeping biomass in the reactive zone; (b) inoculation is a critical step and measurements should be carried out to check the initial distribution of microorganisms and its evolution over time; (c) electron acceptor and nutrient supply is usually required, but oxygenation into anaerobic aquifers can be critical.