Photo: Courtesy of the Port of Antwerp.
Several technologies exist to treat polluted dredged material:
- In situ (“in place”) remediation refers to the clean up of contaminated soils and groundwater without removing contaminated media from the subsurface, typically through the use of physical and/or chemical processes
- Ex-situ remediation involves the removal of contaminated media, either for off-site disposal or for on‑site treatment and subsequent return to the subsurface
The treatment mechanisms can range from physical/chemical, biological to thermal treatment technologies:
- Physical/Chemical treatment technologies can potentially remove high levels of metal contaminants in situ. Many metal species can be simultaneously removed. Despite their effectiveness, they generally cost a lot, due to the specialized devices, machinery, and chemicals. This category of treatment includes soil vapor extraction, solidification/stabilization, chemical oxidation, soil flushing, and electrokinetic separation.
- Biological treatment technologies use a process whereby contaminants in soil, sediments, sludge, or groundwater are transformed or degraded into innocuous substances such as carbon dioxide, water, fatty acids, and biomass, through the action of microbial metabolism. This technology is commercially available for treating fuel contamination. This category of treatment includes bioventing and phytoremediation.
- Thermal treatment technologies raise the temperature of the contaminated soil to approximately 260 °C for a specified period of time by exposing it to hot gases (i.e. heated air), volatilizing the contaminants, and destroying them in an afterburner. The techniques available include electrical resistance heating, steam injection, and extraction, conductive heating, radio-frequency heating, and vitrification.
An example of ex-situ treatment of dredged material is the Amoras project which became operational in 2011 in the port of Antwerp, Belgium. Water is removed from the soil by chamber filter presses, after which the filter cake can be disposed of in a controlled manner. This joint project by the Flemish government and Antwerp Port Authority offers a sustainable solution for the processing and disposal of dredged soil from the port. In parallel with Amoras, the Vamoras project looks at ways of recycling the filter cake in e.g. bricks, lightweight aggregate, or concrete for foundations.