Removal of natural organic matter by coagulation-flocculation: A pyrolysis-GC-MS study

The removal of the natural organic matter (NOM) in the Seine river water sa mpled at Le Pecq (France) was carried out by using three coagulants: ferric chloride, aluminum sulfate, and aluminum polychlorosulfate (PACS). The eff iciency of the coagulation-flocculation process depended on the pH. The bes t 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 i n the raw and clarified water as well as in the flocs was analyzed by pyrol ysis-gas chromatography-mass spectrometry (Py-GC-MS). Using this technique on the flocs formed with ferric chloride, a selectivity of this coagulant f or polyhydroxyaromatics (PHA) was shown. A preferential binding was also ob served between PACS and polysaccharides (PS). No such trend could be observ ed with aluminum sulfate. These results were confirmed and refined by PyGC- MS analyses on the different mass fractions of the clarified water obtained by gel permeation chromatography.