Study of Biodegradation Processes of BTEX-ethanol Mixture in Tropical Soil

In Brazil, gasoline is currently blended with ethanol and both compounds may contaminate the environment when spills occur. Ethanol preferential biodegradation delays gasoline degradation in the aquifer, as previously observed; in unsaturated soil a delayed recovery of culturable bacteria and removal of residues in the presence of ethanol suggest a similar situation. This study monitors microbial degrading activity in unsaturated soil with BTEX and BTEX-ethanol mixtures under tropical conditions as well as the effects of bioventing on contaminants degradation. Enzymatic activity was quantified by measuring fluorescein-diacetate hydrolysis by microorganisms, which determines total degrading activity in soil. As microbial enhanced activity may alter soil electromagnetic properties, soil dielectric constant shifts were monitored using Time Domain Reflectometry (TDR), while chemical analyses evaluated contamination residues throughout the experiment. Results suggest that ethanol delays BTEX biodegradation and that bioventing may compensate for this delay by providing oxygen for the continuation of microbial activity. Contamination and bioventing stimulated soil microbiota, while culturable populations were inhibited by contamination, showing soil toxicity. The presence of ethanol caused a higher and longer-lasting boost in enzymatic activity; TDR measurements did not follow these activity shifts, proving not to be an adequate tool for evaluating microbial activity in these experimental conditions. Residual BTEX were detected only in ethanol-containing non-ventilated soils after contamination. The set of results suggests that ethanol could delay BTEX degradation because of its constitutive degradation by soil microbiota, but this effect may be bypassed by bioventing.