Physico-chemical and flocculating properties of a bioflocculant, producing by a Serratia plumuthica isolate, were studied. The bioflocculant was identified as an acid polysaccharide consisting of galactose, talose, glucose, mannose and galaturonic acid in a ratio of 34.5:5.1:24.5:29.6: 9.2. Its molecular weight was estimated to be 1.8×106. The bioflocculant was found to be effective for flocculation of a kaolin suspension, when added at a concentration of 1~10 mg/L, in a broad pH range of 2~9 and temperature range of 10~80°C. Its flocculating activity was synergistically stimulated by the bivalent or trivalent cations such as Ca2+, Mg2+, Al3+ and Fe3+. In addition, it could efficiently flocculate a variety of suspensions, including paper-making wastewater, oil-producing wastewater, black ink, alga cell suspension and activated sludge.
