Microbial community response to a release of neat ethanol onto residual hydrocarbons in a pilot‐scale aquifer tank

Abstract

The microbial community response to a neat ethanol release (E100, 76 l) onto residual hydrocarbons in sandy soil was evaluated in a continuous-flow 8 m(3) pilot-scale aquifer tank, simulating a release at a bulk fuel terminal. Microbial genotypic shifts were assessed using quantitative real-time PCR analysis. High ethanol concentrations in the capillary fringe at potentially toxic levels, exceeding 100,000 mg l(-1), were tolerated by the microbial community. The high biochemical oxygen demand exerted by ethanol rapidly induced anaerobic conditions, and both methane production (up to 1.2 mg l(-1)) and growth of putative methanogenic Archaea (up to 10(6) gene copies per g of soil) were observed in shallow groundwater and soil samples 75 cm down gradient from the source. Aerobic conditions returned after ethanol was flushed out of the system, approximately 45 days after the spill (less than 7.5 pore volumes flushed). Total Bacteria growth coincided with ethanol migration and availability, which was restricted to a relatively thin layer at the capillary fringe and water table interface. The concentrations of bacteria harbouring the aerobic catabolic genes dmpN (coding for phenol hydroxylase) and to dC1 (coding for toluene dioxygenase) increased (up to 100x) down gradient from the source, likely as a result of both fortuitous growth on ethanol and on aromatic hydrocarbons mobilized by ethanol. Growth of hydrocarbon degraders was corroborated by denaturing gradient gel electrophoresis analysis showing proliferation of Azospirillum and Brevundimonas spp., which are bacteria commonly associated with microaerophilic hydrocarbon degradation. Nevertheless, the relative abundance of hydrocarbon-specific degraders (as a fraction of total Bacteria) decreased as other bacteria grew to a higher extent. Overall, the observed growth of hydrocarbon degraders suggests a potential enhancement in aerobic natural attenuation in shallow aquifers after ethanol and its degradation by-products are degraded or flushed from sites impacted by ethanol-blended fuels.

Analytical model for BTEX natural attenuation in the presence of fuel ethanol and its anaerobic metabolite acetate

“…Therefore the presence of ethanol and ethanol-derived acetate in groundwater can contribute to longer BTEX plumes (Ruiz-Aguilar et al, 2002;Corseuil et al, 2011) increasing the risk of human exposure ). These observations have been corroborated by laboratory studies (Corseuil et al, 1998;Da Silva and Alvarez, 2002;Cápiro et al, 2007Cápiro et al, , 2008, field research (Ruiz-Aguilar et al, 2002;Corseuil et al, 2011) and modeling studies (Heermann and Powers, 1998;Mcnab et al, 1999;Molson et al, 2002;Gomez et al, 2008;Alvarez, 2009, 2010). Nevertheless, the intensity of these effects can be system specific, which underscores the need for simple models that facilitate preliminary risk assessment and evaluate the potential performance of natural attenuation.…”

Spatial and temporal dynamics of organohalide-respiring bacteria in a heterogeneous PCE–DNAPL source zone

“…Following collection of the final round of aqueous samples from the sideports at the termination of the experiment (day 525, PV 116.2; Table 1), solid phase samples were obtained from a 1 cm radius around each sideport by destructive sampling. To enumerate dechlorinating bacteria by qPCR, DNA was extracted from solid and aqueous samples following established protocols (described in the Supplemental material) (Amos et al, 2009;Cápiro et al, 2008Cápiro et al, , 2014.…”

Influence of the Anaerobic Biodegradation of Different Types of Biodiesel on the Natural Attenuation of Benzene

“…For example, acetate concentrations above 64 mg/L (Corseuil et al 2011a) and 75 mg/L (Ramos et al 2013) were found to be responsible for the inhibition of anaerobic biodegradation of benzene. Also, ethanol has been shown to decrease the relative abundance of benzene, toluene, and xylene degrading bacteria (Cápiro et al 2008).…”