Real-time geochemical data improves outcome of bench-scale treatability study

The In-Situ team recently visited Dr. Clint Bickmore with B Street Technologies at his lab at the TinkerMill in Longmont, CO, to observe a bench-scale treatability study involving contaminated soil and groundwater.  Dr. Bickmore has a PhD from the University of Michigan in materials science and engineering, and has extensive experience designing and implementing environmental remediation projects across the country.

Reduction of Chrome 6 to Chrome 3The contaminants of concern in the pilot study consisted of hexavalent chromium (chromium 6) and chlorinated ethenes (TCE). Chromium 6 is a metallic chemical that originates as a contaminant in the environment from the discharges of dye and paint pigments, wood preservatives, chrome plating liquid wastes, and leaching from hazardous waste sites. Chromium 6 is readily soluble in water. Under high Eh (oxidizing) and alkaline (pH above 7) conditions, it can be predominant in groundwater and is toxic to humans and microbial populations. However, in the presence of organic matter, ferrous iron (Fe II) and sulfide, Cr6 can be readily reduced to Cr3 and immobilized. TCE is a common solvent used for degreasing metal parts and can be degraded using anaerobic bioremediation.

The pilot study involved pumping ferrous sulfate and sodium dithionite, both reducing agents, through a column of soil excavated from the site, followed by a sodium hydroxide chaser to restore pH.  Geochemical and physical parameters including temperature, pH, ORP, dissolved oxygen, electrical conductivity and turbidity were monitored in real-time using the Aqua TROLL 600 Multiparameter Sonde in a flow-through cell connected to the column.

Dr. Bickmore adding amendments to the columnVuSitu Mobile App: Geochemical parameters showing anaerobic conditionsDuring the pilot, pH, DO and ORP data confirmed that anaerobic conditions had been achieved.  Column water was then tested with a Hach test kit and showed no presence of chromium 6.   A neutral pH, critical to the presence and activity of the microbial population in groundwater, was then restored with sodium hydroxide, setting the stage for the bioremediation treatment phase to degrade the TCE.

Aqua TROLL 600 with wireless BluetoothAfter 36 hours of continuous exposure to harsh contaminants and chemical amendments, the Aqua TROLL 600 pH sensor (patent-pending) was validated in pH buffers 4, 7 and 10, to confirm that the readings were free of drift.  As the chromium 6 precipitated it left a residue on the wetted materials.  The antifouling wiper system effectively eliminated the film and insured the integrity of the data throughout the test.  All other sensors performed within spec as well.

The next step in the pilot will determine whether emulsified vegetable oil (EVO) or cheese whey will be used as a substrate to stimulate anaerobic biodegradation of the remaining TCE.   Once the substrate is selected, a field treatability pilot will be conducted using Aqua TROLL 600 Multiparameter Sondes, deployed 125’ below ground surface in observation wells at the site to capture breakthrough in real-time.

Access to real-time geochemical data during all phases of an injection pilot can reduce uncertainty, enable dynamic decision-making, and better inform the full scale design.  It can also insure proper placement of the amendment material in the subsurface, reducing chemical costs and improving the treatment outcome.

To learn more about real-time monitoring at contaminated sites, please visit our Remediation page, or fill out the form below and one of our application specialists will be in touch.

Resources:

TinkerMill
Chromium 6
Under high Eh (oxidizing) and alkaline (pH above 7) conditions
Neutral pH