Pilot Studies of Bioremediation of the Exxon Valdez Oil in Prince William Sound Beaches, Alaska: 2010-2011

Lingering oil from the Exxon Valdez oil spill persists on some beaches in Prince William Sound, Alaska, more than 20 years after they became contaminated. Bioremediation was tested in pilot-scale studies during 2011 and 2012 to determine whether this technology could be used to restore these sites. Pilot-scale bioremediation systems were installed at four sites with lingering contamination in 2011 and at two of those sites in 2012.

The technology relied on delivering solutions of dissolved oxygen (at 40 mg/L) and nutrients (nitrogen at 20 mg/L and phosphorus 2.0 mg/L) into the beachest to enhance oil biodegradation. Sediment samples were obtained to analyze for oil and microbial communities, and pore water samples were taken to analyze for oxygen, nutrients (nitrogen and phosphorus), and salinity. There was no clear temporal or spatial pattern of behavior of oil (obtained as total extractable material from the sediments). The sum of the polycyclic aromatic hydrocarbons (PAH) and dibenzothiophene, labelled herein as total PAH (TPAH) was used as the main indicator of bioremediation. The TPAH biodegradation rate at PWS3A44 was 72% and that at EL056C in 2011 was 35% suggesting very effective bioremediation. However the rate at other beaches and/or in other years varied from 13% to 26%, with an average of 16%, which reflects a four-fold enhancement on the natural biodegradation rate of oil in beaches, which was estimated at less than 4% per year. In general, the concentration of dissolved oxygen (DO) in the pore water increased following treatment and so did the concentrations of nitrogen from nitrate and phosphorous. Microbial counts using the most probable numbers (MPN) revealed that the MPN of PAH degraders was an order of magnitude smaller than that of alkanes, and it decreased with time, suggesting depletion of the PAH. A beach survey for bioremediation potential revealed that two beaches out of 23 received a “bio-score” of 100 suggesting that bioremediation on these beaches would be effective in removing the TPAH at approximately 16% per year.