BIO-BARRIER FOR HIGH CONCENTRATIONS OF KETONES, ALCOHOLS & VOCs
Sami A. Fam, Ph.D., P.E. L.S.P., David Falatko, P.E., Jason Blackburn, P.G., Innovative Engineering Solutions, Inc.,
George Pon, Ph.D., Bioremediation & Treatability Center. Michael Gaudette, Univar USA Inc.
We have been operating an interim measure, flow-through, bioremediation treatment trench since September 2006. The trench intercepts groundwater contaminated with ketones, alcohols, glycols, aromatic VOCs and chlorinated VOCs thereby preventing contaminants from entering a nearby creek. The influent groundwater to the treatment trench has a chemical oxygen demand of nearly 3,200 mg/L from total alcohol, ketone and VOC concentrations of approximately 700 mg/L. The trench remediation system delivers air flow to provide sufficient oxygen (and other amendments) to enhance the biodegradation of the ketones (acetone, MEK and MIBK), alcohols and glycols, and to volatilize the trace amounts of chlorinated VOCs present. The bioremediation trench is 170 feet long and approximately 10 to 12 feet deep and is located 20 feet upgradient of the creek. A potassium bromide tracer test indicated that the trench receives an approximate groundwater flow of 1 gallon per minute and provides approximately 5 days residence time.
Microcosm testing that was conducted indicated that pH adjustment was required (to raise the pH from 5) and inorganic nutrients were deficient in the groundwater. The low pH was likely due to carbon dioxide and acetate build-up (from upgradient biodegradation). The microcosm testing indicated that a 14 day retention time was required for 100 percent degradation of the ketones; however, the full scale system has achieved 99% removal of contaminants with a much lower residence time (~5 days). This is due to the healthy biofilm that has grown within the trench.
Meeting the very high oxygen demand has been challenging but we have met the demand with an aggressive oxygen delivery system and minor system adjustments during operations, The trench design includes groundwater circulation for oxygen distribution, addition of some pure oxygen at the areas of highest oxygen demand, and trench-wide aeration with a 260 cubic feet per minute positive displacement blower. The remediation system has operated extremely well with relatively minor maintenance needs (1 day per week) in comparison with a groundwater pump & treat system that could accomplish a similar objective but would be more prone to biological fouling and have greater maintenance issues. Downgradient groundwater quality from the trench has also improved significantly due to the presence of excess oxygen and amendments added to the aeration trench. Such significant downgradient groundwater quality improvement could not have been accomplished by a groundwater pump & treat system in as timely a manner.
