Bench-Scale Evaluation of Bioremediation for the Treatment of Sediments from the Ashtabula, Buffalo, Saginaw and Sheboygan Rivers

Final Report

Prepared by

W. Jack Jones
Rochelle Araujo
John E. Rogers

Ecosystems Research Division
National Exposure Research Laboratory
U.S. Environmental Protection Agency
Athens, Georgia

For the

Assessment and Remediation of Contaminated Sediments (ARCS) Program
U.S. Environmental Protection Agency
Great Lakes National Program Office
Chicago, Illinois

ABSTRACT

The potential of microbial degradation for the reduction of organic contaminants was examined in sediments from four Areas of Concern in the Great Lakes Region: the Ashtabula, Buffalo, Saginaw and Sheboygan Rivers. Only indigenous organisms were tested in the bioremediation study; organisms from other sites or genetically engineered bacteria were not employed. The ability of anaerobic bacteria to remove chloride ions (reductive dechlorination) from polychlorinated biphenyls (PCBs) was tested at three of the four sites. Separate tests were undertaken to assess the ability of aerobic microorganisms to degrade poly-nuclear aromatic hydrocarbons (PAHs) in sediments from the Buffalo River.

Bench-scale studies were performed to determine the dechlorinating potential of natural bacteria for biotransformation of historically contaminated (PCB) sediments and assess enhancement of dechlorinating activity via nutrient addition. PCB-contaminated sediments from the Ashtabula River, the Saginaw River, and the Sheboygan River were tested for their ability to dechlorinate "historical" PCBs and highly chlorinated PCB congeners (added to samples) under anaerobic conditions. PCB-contaminated Ashtabula River sediments were spiked with 2,3,3',4,4'-pentachlorobiphenyl (Penta-CB), 2,3,3',4,4',5-hexachlorobiphenyl (Hexa-CB), and 2,2',3,4,5,6,6'-heptachlorobiphenyl (Hepta-CB). Dechlorination of the added Penta-CB, Hexa-CB, and Hepta-CB congeners was observed after respective lag periods of 5, 3, and 4 months. Significant dechlorination occurred after 6 months when the sediment was spiked with combinations of either two or all three congeners. The average number of chlorines per biphenyl decreased from 5.9 to 3.1 in Ashtabula River sediments amended with a combination of all three congeners. PCB-contaminated sediments from the Saginaw River were amended with Aroclor 1260 in the absence and presence of inorganic nutrients [revised anaerobic mineral medium (RAMM)]. Sediments amended with Aroclor 1260 plus modified RAMM exhibited an increase in the mole percent of mono-, di-, and tri-chlorobiphenyl (CB) homologs and a decrease in the mole percent of homologs with higher numbers of chlorine atoms per biphenyl when compared to unamended controls. In experiments amended with Aroclor 1260 only, an increase was observed in the mole percent of only the mono- and di-CB homologs; the mole percent of the remaining homolog groups decreased. PCB contaminated Sheboygan River sediments were amended with 5, 10 and 20 mg/L of 2,2',3,3',4,5,6,6'-octachlorobiphenyl (Octa-CB). The percentages of Octa-CB remaining in the samples after anaerobic incubation for 8 months ranged from 10 to 35 percent. A decrease in the higher chlorinated (5 to 8 chlorines per biphenyl) homologs, including the added Octa-CB, and a corresponding increase in the lower chlorinated (1 to 3 chlorines per biphenyl) homologs, was observed. The major products of reductive dechlorination of Octa-CB amended sediments were di-CB congeners.

Sediments from Buffalo River were found to be contaminated with PAHs at concentrations ranging from 0.37 mg/kg for fluorene and benz (b) fluoranthene to greater than 10 mg/kg for fluoranthene and pyrene. The indigenous microorganisms from Buffalo River were capable of quickly degrading two- and three-ring PAHs and slowly degrading four-ring compounds, but showed little activity on compounds with greater than four rings. Each of the two- and three-ring compounds supported growth of sediment bacteria in mineral media; the compounds with four rings and higher did not support growth.

An enrichment culture was developed by exposing Buffalo River sediments to each compound in a mixture of 16 PAHs and combining the cultures adapted to each of the compounds to form an enrichment mixture with a wide range of degradative activity. Oxygen did not limit degradation of PAHs by the enrichment culture in sediment slurry experiments. Additions of phosphate, either alone or with nitrogen, enhanced the rate of degradation as measured by the mineralization of pyrene; additions of nitrogen as ammonium nitrate decreased the rate slightly. The addition of organic matter extracted from sediment increased the initial rate of pyrene mineralization by supporting faster growth of the degrader populations. Trace metals were not inhibitory to degradation of PAHs in aerated systems. The presence of additional PAHs decreased the rate of mineralization of pyrene; this inhibition could be reduced by treating the sediment slurries with hydrogen peroxide.

The enrichment culture, when added back to non-sterile sediments (bioaugmentation), did not enhance degradation at inoculation densities below 10⁶ cells/ml. Above that density, mineralization of pyrene was first-order, indicating that growth of the bacteria was not needed to initiate degradative activity.

Sediment had both an inhibitory and a stimulatory influence on the rate of degradation of pyrene. The stimulatory effect could be explained by the utilization of sediment organic carbon as a growth substrate by the bacteria. However, at sediment slurry concentrations above 5%, the rate and extent of degradation decreased with increasing sediment slurry concentrations due to sorption of the compound.

Triton X-100, at concentrations both above and below the critical micelle concentration (CMC), inhibited the mineralization of pyrene when added during the growth phase of the organisms. When the surfactant was added after mineralization of the available phase of the PAH, "solubilization" of the remaining PAH by the surfactant resulted in slight increases in mineralization.

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