Role of mixed surfactants for hydrocarbons removal from real marine sediments: Removal efficiency and residual phytotoxicity after sediment washing treatment

Abstract

Contamination of sediments related to human activities represents one of the most challenging environmental threats, with a special concern to petroleum hydrocarbons, as certain types can be mutagenic and carcinogenic. In the present study, the effectiveness of different surfactants: Polyoxyethylene (20) sorbitan monooleate or Polysorbate80 (Tween 80), Rhamnolipids and Sodium Dodecyl Benzensulphonate (SDBS) was investigated in washing treatment for the remediation of marine sediment characterized by hydrocarbon-contamination. The impact of treatment on the phytotoxic features of the washed sediments was investigated. The surfactants effectiveness was tested at different concentrations (ranging from 0.2 % to 0.6 % in weight), alone or as a mixture. An experimental laboratory-scale apparatus was set up for the simulation of a sediment washing intervention. The washed samples were subject to phytotoxicity tests, by means of germination index (GI). Results highlighted that the use of individual surfactants increased the efficiency of hydrocarbons extraction compared to flushing test with water (15 %, 20 %, 42 % and 44 % for water, 0.2 % by weight of Rhamnolipids, SDBS and Tween 80), even if the increase of surfactant concentration was not decisive in terms of removal efficiency. In contrast, the use of mixed surfactants increased the removal rate, up to 70 % (0.4 % and 0.2 % by weight for SDBS and Tween 80), suggesting that the formation of mixed micelles might be beneficial in process performance. The use of SDBS determined a decrease of GI values, thus suggesting a negative impact on phytotoxicity, whilst the combined use of Tween 80 and Rhamnolipids was characterised by higher values of GI, suggesting a more eco-compatible behaviour.