Evaluation of bioventing on a gasoline-ethanol contaminated undisturbed residual soil.

Remediation methods for environmental contamination problems based on physical or chemical processes frequently present low efficiency and/or high costs. On the other hand, biological treatment is being proved to be an accessible alternative for soil and water remediation. Bioventing is commonly used for petroleum hydrocarbon (PHC) spills. This process provides better subsurface oxygenation, thus stimulating degradation by indigenous microorganisms. In Brazil, gasoline and ethanol are routinely mixed; some authors suggest that despite gasoline high degradability, its degradation in the aquifer is hindered by the presence of much rapidly degrading ethanol. The present study evaluates a bioventing treatment of a gasoline-ethanol contaminated undisturbed residual soil from Rio de Janeiro. Contamination and treatment effects were monitored by conventional microbiology methods, chemical analysis, and ground penetrating radar (GPR) measurements. Results of culturable bacterial population counts show the effect of contamination and bioventing on the microbiota of gasoline and gasoline-ethanol containing soils; however, GPR responses to these variations are not conclusive and still need to be assessed.

Laboratory tests for reactive barrier design.

Owing to limitations of pump-and-treat, several technologies are being investigated for groundwater treatment. One of the most promising is the treatment of contaminants through the use of reactive barriers installed in situ, especially in the case of aquifers contaminated with chlorinated solvents. This work presents results of batch and column tests with metallic iron and some chlorinated solvents (1,2-DCA, 1,1,2-TCA and TCE). Such tests provided means to evaluate the degradation rates of these compounds and their byproducts. It is concluded that the reductive dechlorination with metallic iron can have different results, depending on the type of contaminant. Some contaminants may not present any degradation, or they have a half-life time so high that the use of the reactive barrier technology may not be practical. Furthermore, the formation of chlorinated byproducts, eventually more toxic than the original contaminant and that are not degradable using this same technology, emphasises that the treatment of aquifers should be sequential.