Use of biochar as alternative sorbent for the active capping of oil contaminated sediments

Biochar was tested as an active capping material for oil spill contaminated sediment and its performance was compared to activated carbon and organoclay. Polydimethyilsiloxane fibers were used as passive samplers to evaluate the vertical porewater concentration of selected polycyclic aromatic hydrocarbons through the sea-sediment and the capping layer (1 cm resolution). Experiments were carried out on the laboratory scale using 7.5 cm (∼500 g) of contaminated sea-sediment that were capped with 3 cm (∼150 g) of capping materials. The porewater concentrations of the polycyclic aromatic hydrocarbons were compared using a reactive-diffusion model. Biochar showed a greater capping efficiency than activated carbon and organoclay. For example, anthracene porewater concentrations in the first centimetre of capping material, after 1 month, were reduced by 69%, 56% and 99% respectively for activated carbon, organoclay and biochar. The porewater concentrations were used to model the long term (≥12 months) behaviour of various cap configurations with a numerical simulations. Biochar can be considered a cost-effective alternative to the more consolidated sorbent materials.