Kent Armstrong
TerraStryke Products, LLC
Andover, NH, USA
Richard Schaffner, Jr., CGWP
Schaffner Applied BioGeosciences, LLC
Proof-of-Concept study evaluating efficacy of biostimulation additive TPHenhanced™ to 1) enhance respiration of native heterotrophic bacteria; 2) enhance dissolved-phase petroleum hydrocarbon (PHC) destruction; and, 3) expedite solubilization of residual source mass, under anaerobic conditions. Site abandoned upstream oil-gas facility with saturated-soils/groundwater, proximate to production-water retention pond, contaminated with PHCs (specifically Benzene) above Colorado regulatory standards.
Baseline [BTEX] ranged from 2.4 mg/L to 10.6 mg/L, respectively. March 2017 impacted saturated-soils amended using passive release sock (PRS) deployment units; suspending one PRS-unit into each of 26 pre- existing deployment-nodes, established for previous ISCO event. Each node extends ≈10ft bgs with the bottom 5-feet screened within the saturated soil column. PRS units create an ≈3-5-foot AOI. In April 2017 a second deployment event occurred with no additional deployments performed thereafter. Two monitoring locations evaluated: one located within (MW-07), the second (MW-04) outside-downgradient the impacted pond. Five performance monitoring/sampling events completed during 9-month evaluation.
Results: 1) with increased additive availability Oxygen Reduction Potential (ORP) values increased; 2) enhanced reductions in dissolved-phase PHC contaminants were observed while under anaerobic conditions; and 3) expedited solubilization of residual source mass was realized, presumably due to increased viability of the growing heterotrophic bacterial community. We propose, the combined effects of the additive enhance the collective secretion of natural biosurfactants by the native microbial communities, effectively increasing contaminant bioavailability while concurrently increasing combined microbial efficiencies associated with maximizing PHC degradation.
Observations: with increased additive loading dissolved-phase [BTEX] decreased 84% (MW-04) and 79% (MW-07) demonstrating enhanced microbial activity. We propose, as microbial populations grew with the introduction of the additive, solubilization of residual source mass was naturally expedited, as seen as a 500%-1,000% increase in [BTEX] following pre-solubilization (initial) decreases. At peak solubilization, rapid additive utilization is observed followed by dramatic decreases in dissolved-phase [BTEX]. Specifically, from peak bioavailability [Benzene] decreased 98.4%, [Ethyl Benzene] 83% and [Xylenes] 97.4% at MW-04.
We propose additive enhanced bacterial populations utilized the additive as alternative electron acceptor and dissolved-phase [BTEX] as electron donor, i.e. an energy-carbon source providing cellular building block-materials to grow the PHC degrading ‘community’. PHC degradation continued as additive availability was exhausted suggesting the duality of the additives components; one being the ability to enhance native heterotrophic microbial respiration and PHC destruction, the second being the ability to stimulate syntrophic relationships between the degrading community as the additive is exhausted via endogenous decay. It appears the enhanced native microbial populations naturally recycle additive components to support continued PHC destruction.
Conclusions: the introduction of the additive enhanced the unicellular degrading community’s ability to degrade substrate(s) that neither could degrade alone while, concurrently increasing contaminant bioavailability. It appears TPHenhanced stimulates microbial respiration, eliminates rebound ‘up-front’ and enhances the destruction of dissolved-phase and residual mass PHCs while maintaining anaerobic conditions.