Tipping the Scale

Dec. 6, 2016
Breaking down a breakthrough treatment for PCBs

About the author: Bob Ferguson is a consultant in water and wastewater product safety, certification, analysis and treatment, and is a frequent author on water and environmental topics. Ferguson can be reached at [email protected], or follow him on Twitter @Ferguson9806.

The Institute of Marine and Environmental Technology (IMET) in Baltimore, a part of the University System of Maryland, is a research institute that focuses on marine biotechnology, including remediation of marine environments, sustainable aquaculture, biomedicine, genomics and marine bioenergy.

These topics are especially important for a port city like Baltimore, built around the Inner Harbor, in a state that surrounds Chesapeake Bay and is supported by the Eastern Shore fishing industry.

As an example of the work they do, the scientists at IMET were the first to grow Maryland crabs completely through their lifecycle in aquaculture (reversing what was a declining Chesapeake Bay crab population). Maryland crabs are now far less endangered (and that is good news, especially for those of us who love Maryland crab cakes!).

I had a chance to meet an IMET scientist, Kevin Sowers, Ph.D., professor and associate director for IMET. An expert in anaerobic bacteria and bioremediation, Sowers has been working on a technology designed to remove polychlorinated biphenyls (PCBs) from aquatic sediments.

PCBs in U.S. Waterways

W&WD readers know that PCBs have been an environmental problem for a long time. Manufacturing and use of PCBs was banned in the U.S. in 1979 and worldwide in 2001, but they are stable compounds that persist in the environment and bioaccumulate in aquatic organisms. They are potential carcinogens and endocrine disrupters and, as such, a threat to seafood and human health.

Many waterways are impacted by PCBs. In Sowers’ publications, he reports that more than 1,000 U.S. waterways are under fish advisories and 23% of these are due to PCBs. In Maryland, for instance, there are fish advisories for more than 50 bodies of water due to PCBs. Across the U.S., this represents an estimated 6 million lake acres and 132 miles of PCB-contaminated sediments.

These sites and sediments have not been cleaned up because of the cost and difficulty of implementing the available options. Contaminated sediment dredging is typical, but the process is disruptive to the body of water being treated and can serve to distribute the contamination downstream. The contaminated sediments typically are landfilled, but not treated, potentially only delaying the problem to the future. Capping the sediments in place is another option, but this also only isolates the contamination in place. Both options are enormously expensive.

When I was working in bioremediation, there were a few technologies capable of biologically reducing PCBs, but all were only partially effective, with none able to reduce PCBs to safe or useful levels.

Sowers and his team apparently have changed all of this and may have a breakthrough in the treatment of PCBs.

PCB Remediation Solution

Sowers is an expert in anaerobic bacteria—exactly the type of bacteria that would be expected to inhabit sediment deep in rivers and lakes. Sowers and his team have worked for years to identify and isolate the bacteria—a combination of anaerobic and aerobic—in these sediments that can use and degrade PCBs. Once they identified the specific anaerobic species (anaerobic halorespirers) that can strip the chlorines from the PCB molecules and the aerobic cells then that can degrade the rest of the compound, and could culture both in their lab, they had two goals. First, find a way to increase the concentration of the cells, and second, effectively deliver the concentrated cells into the sediments in a way that allows them to access and degrade the PCB contamination.

Sowers and his team worked with a local Maryland company, Sediment Solutions, to use a pelletized activated carbon media that could effectively serve as a delivery system to inoculate a high concentration of cells into the sediment and provide a substrate for biofilm formation to degrade the PCBs. This inoculated media is sprayed into the body of water (Sowers showed me photos of his team standing in boats spraying the media with an airhorn); the media sinks to the bottom and covers the sediment with a relatively thin layer, and then natural movements of benthic organisms in the sediment allow the media to mix into it and thoroughly inoculate it with the active cells.

In laboratory pilot studies, Sowers found that this method achieved up to 80% degradation of total PCBs in less than six months. If you are not familiar with PCB bioremediation, this is a dramatic reduction in concentration in a short period of time. In a field study, at a contaminated wetlands site at the Marine Corps base at Quantico, Va., the technology achieved greater than 50% reduction of PCBs in less than 14 months.

One particularly interesting fact about this technology is that toxicology and treatability tests indicated that the remaining PCBs not degraded by the technology no longer are bioavailable. The PCBs remaining in the sediment are thoroughly sequestered by being absorbed to the organic material in the sediment and the activated carbon used as a carrier and no longer will have an impact on aquatic life.

In other words, the “problem” is 99% solved.

Sowers and his team have used the technology in wetlands, a sewage treatment pond, a submerged factory basement in Delaware, Baltimore Harbor sediments and a remote island in Hawaii; and these projects are showing great promise. Sowers cites in his publications that less than 1% of PCB sites have been remediated, primarily due to the high costs of treatment. This aligns with my experience in environmental remediation: Sites contaminated with recalcitrant compounds can sit for decades.

But I have also seen that better and more cost-effective technologies can “tip the scale” and get these projects moving. Sowers claims that this technology can be implemented for perhaps one-fifth of the cost of dredging, so it looks like he and his team at IMET may be tipping some scales very soon. 

About the Author

Bob Ferguson

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