Transport of Dioxins and Furans Through Geotextiles During Sediment Dewatering

Dredged marine sediment is often dewatered prior to placement or disposal. Sediments contaminated with polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, commonly known as dioxins and furans (PCDD/Fs), present unique challenges for dewatering and disposal due to their toxicity. This issue is prevalent across Canada; the Treasury Board of Canada (2017) lists 157 federally registered contaminated sites with PCDD/Fs and/or PCB contaminated sediments. PCDD/Fs present at even very small levels (i.e. picogram) in water via particulate matter association are not acceptable in most jurisdictions.

Dewatering of sediment using geosynthetic tubes (i.e. geotubes) is becoming common practice, yet the risks associated with PCDD/F transport via geotubes is not well understood or quantified. The long-term objective of this research program is to better understand the transport and fate of PCDD/Fs via particle matter during sediment dewatering using geotubes. It is well established in the literature that PCDD/Fs are strongly associated with particulate organic matter in soil water systems. This research program will use a combination of lab and field studies to assess particulate matter transport, and hence PCDD/F transport, during geotube dewatering. New predictive approaches will be developed for designing geotube dewatering systems involving PCDD/Fs.

The initial research will focus on lab experiments to identify the dominant mechanisms responsible for PCDD/F transport via particle matter from geotubes during dewatering. Lab experiments will use contaminated marine sediments and will involve physical testing using bench scale dewatering techniques. The sediment retained during these tests will be physically characterized. The particulate matter in the effluent will also be characterized using similar methods (i.e. to assess particle transport during dewatering). The role of different geotextiles and filter cake development on the transport of particle matter will also be assessed. Key mechanisms will be evaluated with respect to transport of PCDD/Fs from sediment during dewatering. This portion of the work will involve spiking of sediment PCDD/Fs and evaluating PCDD/F transport during dewatering. The work will also involve evaluating existing filtration performance models to predict the transport of PCDD/Fs during geotube dewatering under differing operational conditions. A field dewatering trial of PCDD/F contaminated sediment will provide opportunity for comparison to lab findings and predictive tools developed in the research will be assessed based on these field trials. This research program will also support the training of several HQP including 2 doctoral, 2 masters and 4 undergraduate students.