Oral communication at Applied Mineralogy Conference, Bristol.

Partner : University of Strathclyde

Authors/presenting : Keith Torrance and Richard Lord

Audience type : Technical

Audience : 43

Title of teh communication : Environmental and economic considerations to the reuse of dredged canal sediments

Abstract : Dredging of Europe's canals, harbours, and waterways generate around 250 million cubic metres of waste sediment, of which only 1% is currently reused, with most disposed of at sea. To make better use of this potential, resource a consortium of universities, port authorities, and canal managers have been undertaking a Interreg-funded project, SURICATES, to investigate the barriers to sediment reuse. In Scotland, Scottish Canals with the assistance of the University of Strathclyde have undertaken pilot-scale projects (up to 15,000 m3 of dredged sediment) on the Union Canal, Forth and Clyde Canal, and the Caledonian Canal from 2019 until 2021. Several approaches, including bioengineering, concrete manufacture and aggregate recovery were implemented, based on the sediment characteristics of each site and the proposed end use of the  recovered sediment. Barriers to sediment reuse fell into three categories; contamination of the sediment from past land use; the geotechnical properties of the sediment, including water and organic carbon content, and logistic considerations. The latter is critical for economic viability, due to the high costs and large carbon footprint of transporting and handling and transporting wet sediments. Organic carbon content in sediment from canals is the primary limiter for geotechnical applications, although this could be reduced through conditioning and treatment. At Laggan on the Caledonian Canal, over 8,000 cubic metres of sediment was removed from the canal using suction dredging, permitting direct pipe transport to adjacent separation lagoons. The design of the lagoons allowed different particle size fractions to be separated and de-watered. Although these dredgings were free of contaminants, its organic carbon content was still an issue. The main takeaways from this pilot study were as follows:"    Suction dredging, in combination with settling lagoons is an effective approach to recovering and separating aggregates and soils from canal sediments."    Hydraulic dredging allows for sediment transport as a slurry by pipeline, which is economically beneficial and has the added benefit of reducing heavy goods road vehicle movements."    The coarse sand fraction rapidly drops out of the slurry and can be readily dewatered for beneficial use. An unexpected observation is that the quality of this fraction appears to be enhanced by the fluvial sedimentary processes, such as channelization, winnowing and reworking that can be observed to occur within the beaching area of the lagoon."    Organic matter in the sediment in this location has a bimodal distribution, with pinecones and wood, large enough to be separated by the screener. However, the bulk of the organic matter content falls within the fine sand and silt fraction ( <0.6 mm) but was mostly separated from the sand and accumulated with the silts and clays in the Lower Lagoon."    The recovered sands and gravels were suitable for the manufacture of concrete and the fine fraction as low fertility topsoil.

Link :