Flocculating property of extracellular polymeric substance derived from a marine photosynthetic bacterium, Rhodovulum sp.

The effect of the extracellular polymeric substance (EPS) derived from a ma rine photosynthetic bacterium, Rhodovulum sp., on the flocculation of kaoli n is described. The amount of EPS obtained and its flocculating activity we re highly dependent on the extraction temperature and duration: high floccu lating activity was obtained at a relatively low temperature (30 degrees C) and long extraction time (60 min). The EPS was classified as a weak-anioni c high-polymer group based on its pH profile, and its promoting effect on f locculation was dependent on the concentration of cationic ions and their v alence. The relative influence of cations on the critical flocculating conc entration (Cs, cr) followed the Schulze-Hardy rule for colloidal flocculati on. This suggests that the promotion of flocculation by the additions of EP S and cations occurred as a result of the synergistic effect of the release of electrical repulsion by the cations and the formation of bridges betwee n the EPS and the cations.