USA – Baltic International Symposium on Advances in Marine Environmental Research, Monitoring and Technologies. Klaipeda, Lithuania. June 15-17, 2004
Global commerce relies heavily on waterborne transportation. Innovative, economical and environmentally sound ways to manage dredged materials, which result from ongoing channel maintenance and harbor development projects, are required to; i) minimize or eliminate potential adverse environmental impacts of contaminated dredge sediment deposition; and ii) facilitate longterm dredge sediment management. We have implemented various environmental biotechnologies as part of larger-scale sediment management programs at several locations. As outlined herein, in situ and ex situ solutions were designed for managing contaminated materials with a focus on yielding renewable materials to reduce the overall reliance upon conventional entombment approaches.
Ex Situ Treatment: Sydney Tar Ponds, Halifax, Nova Scotia: As one of the largest contaminated sites in Canada, over 550,000 m3 of dredged sediment are impacted by PAHs (average 6,000 mg/kg; range of 880 to 27,800 mg/kg., PCBs (from 1.0 mg/kg to 2,600 mg/kg, with contamination concentrated in defined areas), other organics, heavy metals (e.g., 40,600 mg/kg tin), coke and coal fines released over 100 years of industrial activity. The average heating value of the sediment is 19,860 kJ/kg (8,544 BTU/lb), with a range of 7,072 to 28,678 kJ/kg. Sediments generally consist of very loose, medium-sized sand particles with some coarse sands and fine gravel sized coal and coke fragments. In 2002, we conceptualized a “treatment train” that employed dredging, dewatering, particle-size separation, and physical/chemical soil washing followed by electrocoaggulation, solvent extraction, and/or bioremediation to treat metals, PCBs, and PAHs/lowlevel PCB impacts, respectively. Bench-scale treatability studies using aerobic DARAMEND bioremediation technology reduced the concentration of PAHs in sediments (from ca. 4,900 mg/k to <2,000) within 82 days; however the pH of the sediment dropped from 7.2 to 3.8 upon sediment aeration. Scale-up designs were modified accordingly and will be described. Application of similar technology to other sites (Thunder Bay Harbour, Canada; Hamilton Harbour, Canada; and Zeebrugge Harbor, Belgium) will also be discussed.
In Situ Treatment: Former Wood Treatment Site, South Carolina, USA: Various biogeochemical and ecological analyses were used to monitor in situ biodegradation processes as influenced by sub-surface oxygenation (placement of ORCTM) and fertilizer enhancement, and to document the concomitant reduction in sediment PAH concentrations with change in acute toxicity to indicator organisms (Mysidopisis bahia and Neanthes arenaceodentata). Statistical analyses suggested that sediment conditions, other than pH, were not significantly affected by the fertilizer and ORC treatments. The toxicity data also provided very strong evidence that PAH concentrations in sediment were not responsible for the observed acute toxicity; The absence of consistent toxicity findings at a particular sampling location and the absence of a relationship between total PAH (or metals) concentrations and toxicity, indicated that even if remediation were to performed, the observed toxicity might well remain (since its cause was unknown). Results from similar efforts in Salisbury, Maryland and Philadelphia, Pennsylvania (USA) will reinforce the importance of balancing natural attenuation processes in a marine ecosystem that is functioning well with the disruption that would occur if active remediation were to be undertaken.