Characterization of micro-flocs of NOM coagulated by PACl, alum and polysilicate-iron in terms of molecular weight and floc size

Micro-flocs of NOM coagulated by polyaluminium chloride (PACl), alum and polysilicate-iron (PSI) were characterized by flocs size, HPSEC-based molecular weight and the captured content of coagulants-based aluminium and iron. Changes in floc composition with respect to the mass ratios of captured NOM to Al and Fe were examined. Lowering water pH to optimum levels was found to be capable of removing small NOM constituents that are generally difficult to be precipitated at neutral pH levels. For PACl and PSI, the distribution of micro flocs (0.1–5.0μm) reached steady stage after rapid mixing for 30 seconds, with NOM being found existent within the non-coagulated fraction (d<0.1μm) and the coagulated fraction with floc sizes above 5.0 μm (d >5.0 μm). For alum, however, the existence of NOM inside intermediate floc fractions of d = 0.1–1.0μm, 1.0–3.0μm and 3.0–5.0 μm was confirmed.