Purification of firefighting water containing a fluorinated surfactant by reverse osmosis coupled to electrocoagulation-filtration

Extinguishments of large scale solvent fires produce large amounts of water that may contain various fluorinated surfactants depending on the type of firefighting foam used. Due to their chemical nature, fluorinated parts of fluorinated compounds are highly resistant to biochemical and advanced oxidation processes. Therefore the current treatment for the degradation of fluorinated surfactant from water used in fire extinguishment is high temperature incineration of the water in halogen resistant incinerators. This paper aims to propose a process for purifying firefighting water containing fluorinated surfactants. Pilot firefighting waters resulting from heptane fire extinguishment with firefighting foam containing a fluorinated surfactant were produced. Suspended matter was estimated on the basis of turbidity measurement and fluorinated surfactant concentration was determined by high performance liquid chromatography at the laboratory and some samples were analyzed by solid phase extraction and liquid chromatography coupled with mass spectrometry by the Norwegian Institute for Air Research (NILU). Pilot firefighting waters were not suitable for direct membrane processes because of high fouling, hence electrocoagulation and filtration were required. Electrocoagulation with aluminium electrodes at a charge loading of 600 C L-1 followed by filtration were found sufficient to remove turbidity from pilot firefighting waters. Fluorinated surfactant removal was 71-77% and was not significantly increased by higher charge loading. Floc separation in bulk solution was achieved by filtration. Reverse osmosis of pretreated pilot firefighting water and concentrated model solutions of pretreated firefighting water were studied and though flux decline was observed, measured retention rates were 99.94-99.97%, with permeate concentrations down to 10-16 mu g L-1 of fluorinated surfactant at the laboratory scale. The concentrate from reverse osmosis could be recycled in electrocoagulation-filtration. Experimental results indicated that electrocoagulation and filtration followed by reverse osmosis efficiently treated the water from fire extinguishment, which enables a further scale-up work. (C) 2010 Elsevier B.V. All rights reserved.