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Thin-layer capping with reactive sorbents (CAPTIVE)

Project name: Thin-layer capping with reactive sorbents – a cost-effective and environmentally sustainable alternative to dredging of polluted sediment (CAPTIVE)
Project leader: Jonas Gunnarsson, Stockholm University
Participating universities/companies/other organisations: KTH Royal Institute of Technology, Stockholm University
Project period: 2018-2021

The project aims to demonstrate how thin-layer capping with reactive sorbents (TLC) can be implemented as a cost-effective and environmentally sustainable alternative to dredging for in situ remediation of contaminated sediments in Oskarshamn outer harbor and other polluted areas in Sweden.

The project will test the applicability of two types of reactive sorbents: a) the carbonaceous materials: activated carbon (AC) and biochar (BioC) for sorption of hydrophobic organic pollutants (HOCs) and organo-metals (TBT) and b) Polonite® (calcium silicate mineral) for sorption of metals and nutrients (phosphorus). The combination of these two types of reactive sorbents for TLC is highly innovative and has never been tested before. It offers potentially a more sustainable technique to remediate sediments for both HOCs and metals on site (in situ), without the need for dredging.

Methods: 1) The reactive sorbents will be evaluated separately for their sorption capacities of sediment pollutants using laboratory batch tests. 2) The capping efficiency of a composite reactive cap made from a combination of the reactive sorbents (optimized in the batch tests) will be evaluated using mesocosms (close-to-field situation), which allow to quantify the release of contaminants from intact sediment cores, collected in Oskarshamn outer harbor under natural scenarios (with simulated resuspension). 3) Biological effects of
the reactive caps will be evaluated on benthic organisms and on sediment geochemistry. 4) A cost-benefit analysis will be conducted to assess how TLC with a composite reactive cap could be done to remediate contaminated outer harbor of Oskarshamn (not addressed by the current remediation, which focuses on the inner harbor only).

Expected results: The project addresses several major gaps in knowledge on how to use TLC with reactive caps as a new remediation technique. It will reveal: 1) if selected reactive sorbents are suitable, 2) in which doses and mixtures they should be used to achieve high treatment efficiency and low disruption of the benthic community, 3) how the TLC should best be applied, 4) how TLC withstands resuspension over time? We will demonstrate how this innovative technique could be applied in Oskarshamn outer harbor and at other similar contaminated sediment sites in Sweden and internationally.

More information

Poster "Project “CAPTIVE” Capping with reactive sorbents (2018-2021)", in Swedish (pdf 629 kB)