Formatted Title:

Exploratory Pilot Study of a Novel Remedial Dredging Technology for Removal of Contaminated Sediment

Background/Objectives:

Contaminated sediment poses a global challenge, impacting water bodies and ecosystems on a worldwide scale. Pollutants from industry, shipping, agriculture, and urban areas accumulate in sediments, leading to adverse effects on biodiversity and human health. Addressing this widespread situation requires advanced cleanup technologies. This study focuses on pilot testing of the contained dredging system (CDS) at a historically contaminated dock in Antwerp, Belgium. The CDS is specifically engineered for remedial dredging of sites with contaminated sediment in a highly efficient and controlled manner. The objective of the CDS is twofold: (i) to minimize sediment resuspension, also known as turbidity, thereby preventing the spread of contaminants, and (ii) to achieve an optimal dredged material density, making transportation and treatment processes more cost-effective and sustainable. The pilot project location has a history of significant contamination, including perfluoroalkyl and polyfluoroalkyl (PFAS), microplastics, nanoplastics, various chemicals, and heavy metals. The CDS technology will be assessed by measuring and monitoring changes in turbidity, the density of the dredged material, the removal efficiency, and the productivity.

Approach/Activities:

The CDS technology includes an air-filled underwater habitat that is securely positioned into the sediment to the required layer thickness. It utilizes a floater connected to an air outlet, which moves along the sediment surface to auto-regulate internal air pressure by releasing excess air to the water surface. This internal auto-regulation effectively separates the sediment from the water column and prevents any compressed air from escaping the habitat. Because all dredging operations occur within the underwater habitat, maintained at positive internal pressure, sediment resuspension is minimized. Furthermore, by isolating the sediment from the water column, the system makes it possible to maximize the density of the removed sediment. Another significant advantage of the CDS is the capability of the air-filled habitat to facilitate, using cameras and light, real-time monitoring during the dredging process, allowing for immediate intervention when encountering obstacles, debris, munitions, or archaeological artifacts. The CDS model to be employed in this project has a working area of 5 m² and is equipped with two 8-inch dredging pumps. During the project, a soft silt layer, 55 cm deep, and an underlying soft clay layer, 65 cm deep, will be removed. The soft silt layer has a density of 1.15 tons/m³, while the soft clay layer has a density of 1.35 tons/m³.

Results/Lessons Learned:

The technology’s functionality has undergone preliminary investigation in house. However, this pilot project aims to validate its performance in cleaning up contaminated sediment in a relevant environment, based on the following criteria:

1. Turbidity during dredging: The turbidity will be measured in Nephelometric Turbidity Units (NTU) and compared to baseline scenarios. This measurement will determine the extent of sediment suspension and contaminant dispersal during the dredging process.

2. Density of dredged material: The density of the dredged material (kg/m³) will be compared to the density of the local sediment. This comparison will indicate the technology’s efficiency in minimizing the water content of the dredged material.

3. Removal efficiency: The removal efficiency will be measured by comparing the condition of the waterbed before and after dredging. This assessment will help determine how effectively the technology removes sediment.

4. Productivity: Productivity will be measured by calculating the volume of sediment removed per unit of time. This will provide insights into how efficiently the technology operates and its overall throughput.

These findings will offer valuable insights into how well the technology performs in practice and its potential for use in sediment cleanup projects worldwide. The presentation will cover the technology’s operational capabilities, along with results and lessons learned from the pilot project.

Boud Van Rompay

Affiliation

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(Group 1, Poster Board #83) Exploratory Pilot Study of a Novel Remedial Dredging Technology for Removal of Contaminated Sediment