Bioaugmentation for Treatment of Dense Non-Aqueous Phase Liquid in Fractured Sandstone Blocks

Abstract

Laboratory experiments were performed in discretely fractured sandstone blocks to evaluate the use of bioaugmentation to treat residual dense non-aqueous phase liquid (DNAPL) tetrachloroethene (PCE). Significant dechlorination of PCE and growth of Dehalococcoides spp. (DHC) occurred within the fractures. DNAPL dissolution was enhanced during bioaugmentation by up to a factor of approximately 3.5, with dissolved PCE concentrations at or near aqueous solubility. The extent of dechlorination and DNAPL dissolution enhancement were dependent upon the fracture characteristics, residence time in the fractures, and dissolved concentration of PCE. No relationship was observed between planktonic DHC concentrations exiting the fracture and the observed extents of PCE dechlorination and DNAPL dissolution. Measured planktonic DHC concentrations exiting the fracture increased with increasing flow rate and bioaugmentation dosage, suggesting that these parameters may be important for distribution of DHC to treat dissolved chlorinated ethenes migrating downgradient of the DNAPL source. Bioaugmentation dosage, for the DHC dosages and conditions studied, did not have a measurable impact on DNAPL dissolution or dechlorination within the fractures themselves. Overall, these results indicate that bioaugmentation may be a viable remedial option for treating DNAPL sources in bedrock.

Efficient Algorithms for Modeling the Transport and Biodegradation of Chlorinated Ethenes in Groundwater

“…However, recent experimental data provide conflicting evidence as to the relative importance of mobile (pelagic or planktonic) bacteria in biodegradation of chlorinated ethenes (cf. Schaefer et al 2009Schaefer et al , 2010Haest et al 2010). If it becomes clear in the future that mobile bacteria play a significant role in biodegradation of chlorinated ethenes, then the model presented here will need to be amended to account for both stationary and mobile bacteria, perhaps using a method similar to that employed by Clement et al (1998).…”

Microbially enhanced dissolution and reductive dechlorination of PCE by a mixed culture: Model validation and sensitivity analysis

“…In the past two decades, numerous remediation technologies have been developed to treat DNAPL source zones; however, the ability of a single technology to completely remove or destroy all DNAPL mass and reduce dissolved-phase contaminant concentrations below drinking water standards is limited. Among potential in situ remediation technologies, microbial reductive dechlorination has emerged as an attractive DNAPL source zone remedy (Da Silva et al, 2006;Sleep et al, 2006;Schaefer et al, 2010), and as a source zone polishing step to control residual contaminant concentrations following aggressive physicochemical treatment (Mravik et al, 2003;Ramsburg et al, 2004;Christ et al, 2005). During source zone bioremediation, microbial activity lowers dissolved-phase contaminant concentrations, thereby increasing the driving force for contaminant dissolution from the DNAPL to the aqueous phase, a process commonly referred to as bioenhanced dissolution (Yang and McCarty, 2000;Cope and Hughes, 2001;Yang and McCarty, 2002;Adamson et al, 2003;Sleep et al, 2006;Glover et al, 2007;4 Amos et al, 2008).…”

“…Carr et al, 2000;Yang and McCarty, 2000;Cope and Hughes, 2001;Sleep et al, 2006;Amos et al, 2008Amos et al, , 2009Schaefer et al, 2010;Philips et al, 2011). This variability in dissolution enhancement has been attributed to several factors, including differing microbial populations, electron donor limitations, competitive and threshold inhibitions, and competitor populations (e.g., methanogens), as well as changing flow conditions due to gas formation, microbial growth, and experimental design.…”

“…This variability in dissolution enhancement has been attributed to several factors, including differing microbial populations, electron donor limitations, competitive and threshold inhibitions, and competitor populations (e.g., methanogens), as well as changing flow conditions due to gas formation, microbial growth, and experimental design. While bench-scale experiments provide excellent demonstrations of the conditions leading to bioenhanced DNAPL dissolution (e.g., Amos et al, 2009;Schaefer et al, 2010), their use as a design tool for treatment applications in the field is limited. Numerical simulators provide a complementary tool that allows for more efficient assessment of individual parameters and inter-related processes impacting microbial activity, guiding future efforts to understand and optimize in situ bioenhanced dissolution.…”

Dissolution of dense non-aqueous phase liquids in vertical fractures: Effect of finger residuals and dead-end pools

“…A recent study by Yang et al (2012b) showed that increasing aperture standard deviation and/or decreasing correlation length lead to larger amounts of entrapped DNAPL as well as larger sizes of DNAPL blobs, and subsequently cause longer times for complete dissolution. Interphase mass transfer between the DNAPL and the water is also a fundamental component of the remediation processes which are often applied to enhance the mass transfer rates through chemical or biological reactions (e.g., Tunnicliffe and Thomson, 2004;Schaefer et al, 2010;Chambon et al, 2010;Manoli et al, 2012).…”