Formatted Title:

In Situ Bioremediation of a Former Municipal Sewage Treatment Pond Contaminated with High Concentrations of Aroclor 1248

Background/Objectives:

Polychlorinated biphenyls (PCBs) are a widespread contaminant in sediments in the US and a frequent cause of fish consumption advisories. Common practices for remediating PCB-impacted sediments include dredging and transfer to landfills or leaving PCBs in place and preventing exposure to aquatic animals by capping with clean fill or amending sediments with an active material such as activated carbon (AC) or biochar to adsorb PCBs. A more recent in situ method that has been effective is bioremediation, which employs activated carbon (AC) amended with PCB degrading microorganisms for reducing the inventory of legacy PCBs in sediments while also reducing bioavailability to the food chain. The goal of this study was to test the efficacy of bioamended AC for treating sediments contaminated with high levels of PCBs often associated with former industrial sites. A pilot study was conducted in a former sewage treatment pond contaminated with Aroclor 1248 at concentrations up to 1 g/kg. The effectiveness of the treatment for reducing total PCBs levels will be discussed.

Approach/Activities:

Anaerobic organohalide respiring bacteria and aerobic PCB oxidizing bacteria were grown in production-scale bioreactors and applied to sediments using a pelleted AC agglomerate (SediMite™) as a delivery system. An initial study was conducted to optimize treatment parameters in four 0.26 m² caissons constructed from 208 L barrels with the top and bottom ends removed and driven into the sediment. The second phase was conducted in four 7.4 m² caissons in which the bioamendment was mixed throughout the caisson with a sump pump to ensure homogenous mixing throughout the sediment column. Triplicate samples were randomly collected from each caisson by inserting a push core into the sediment to the top of the clay liner. PCBs were extracted with an accelerated solvent extractor (Dionex) following EPA Method 3545 and analyzed by gas chromatography following EPA Method 8082.

Results/Lessons Learned:

Initial tests in 0.26 m² caissons showed that bioremediation had only limited effect in three of the caissons because the highest levels of PCBs were concentrated in the lower half of the sediment column that was impenetrable to the bioamendment through bioturbation activity. In one caisson that was physically mixed with a mud mixer the PCB concentrations in the top 6 cm of sediment were reduced by 87% within 1843 days, but the lower 6 cm was significantly less due to incomplete mixing. Based on these results a sump pump was utilized in the 7.4 m² caissons to ensure mixing of the bioamended SediMite throughout the sediment column. In addition to an untreated control treatments included two types of bioamended SediMite and nutrients without bioamendment to test for biostimulation of indigenous PCB degrading bacteria. All four treatments show similar activity in the 300 days, but there was no further change in the PCB levels in the caisson without bioamendment. In contrast, the PCB levels in the bioamended caisson were reduced by as much as 790 mg/kg, which was 7% or the total PCB mass, after 1582 days and appeared to continue on a downward trend. Results of the field study demonstrate the bioamended SediMite is effective for treating a site with high levels of PCBs with starting concentration as high as the g/kg range. In the case of the AltaVista WWTP the results show homogenizing bioamendment into the sediment column by tilling or sump pumps would be an effective in situ treatment for reducing the high levels of PCBs.

Rayford Payne

Affiliation

Refine Results

In Situ Bioremediation of a Former Municipal Sewage Treatment Pond Contaminated with High Concentrations of Aroclor 1248