Ethanol content in different gasohol blend spills influences the decision-making on remediation technologies

Gasohol blend spills with variable ethanol content exert different electron acceptor demands in groundwater and the distinct dynamics undergone by these blends underscores the need for field-based information to aid decision-making on suitable remediation technologies for each gasohol blend spill. In this study, a comparison of two gasohol releases (E10 (10:90 ethanol and gasoline, v/v) and E25 (25:75 ethanol and gasoline, v/v) under monitored natural attenuation (MNA) and nitrate biostimulation, respectively) was conducted to assess the most effective remediation strategy for each gasohol release. Microbial communities were assessed to support geochemical data as well as to enable the characterization of important population shifts that evolve during biodegradation processes in E25 and E10 field experiments. Results revealed that natural attenuation processes sufficiently supported ethanol and BTEX compounds biodegradation in E10 release, due to the lower biochemical oxygen demand they exert relative to E25 blend. In E25 release, nitrate reduction was largely responsible for BTEX and ethanol biodegradation, as intended. First-order decay constants demonstrated that ethanol degradation rates were similar (p < 0.05) for both remediation technologies (2.05 ± 0.15 and 2.22 ± 0.23, for E25 and E10, respectively) whilst BTEX compounds exhibited different degradation rates (p > 0.05) that were higher for the experiment under MNA (0.33 ± 0.06 and 0.43 ± 0.03, for E25 and E10, respectively). Therefore, ethanol content in different gasohol blends can influence the decision-making on the most suitable remediation technology, as MNA processes can be applied for the remediation of gasohol blends with lower ethanol content (i.e., 10% v/v), once the aquifer geochemical conditions provide a sufficient electron acceptor pool. To the best of our knowledge, this is the first field study to monitor two long-term gasohol releases over various time scales in order to assess feasible remediation technologies for each scenario.