Comparison of the coagulation behavior of different Norwegian aquatic NOM sources

The coagulation behavior of eight natural water samples containing natural organic matter (NOM) was investigated to identify parameters influencing th e process. The coagulation of original water samples is discussed using col our and colloidal charge composition in various molecular weight fractions. Over 40% of colours are given by NOM fractions with molecular weight cut-o ff (MWCO) < 10 kD with one exception. About 1/3 of the colour is given by M WCO fractions > 50 kD for all waters. The optimum coagulant dosage and the colloidal charge were shown to be proportional to the initial colour. This is also valid for dissolved organic carbon (DOC) and for UV-absorbency, whi ch had correlations with colour of R-2 = 0.92 and 0.94, respectively. Large r NOM molecules required fewer amounts of coagulants per removed colour uni t compared with smaller NOM molecules. However, it was not possible to show that the NOM molecule size influences the colloidal charge per colour unit . Zeta potentials at optimum coagulant dosages deviate from zero, indicatin g the presence of other coagulation mechanisms than charge neutralisation. Thus, it is difficult to use zeta potential as the only tool for online dos ing coagulant control strategies. (C) 1999 Elsevier Science Ltd.