Removal of Natural Organic Matter by Coagulation-Flocculation: A Pyrolysis-GC-MS Study

Abstract

The removal of the natural organic matter (NOM) in the Seine river water sampled at Le Pecq (France) was carried out by using three coagulants: ferric chloride, aluminum sulfate, and aluminum polychlorosulfate (PACS). The efficiency of the coagulation-flocculation process depended on the pH. The best results were obtained at pH = 5.5 with ferric chloride and pH = 7.0 with the Al based coagulants aluminum sulfate and PACS.The composition of NOM in the raw and clarified water as well as in the flocs was analyzed by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). Using this technique on the flocs formed with ferric chloride, a selectivity of this coagulant for polyhydroxyaromatics (PHA) was shown. A preferential binding was also observed between PACS and polysaccharides (PS). No such trend could be observed with aluminum sulfate. These results were confirmed and refined by Py-GC-MS analyses on the different mass fractions of the clarified water obtained by gel permeation chromatography.