A soil isolate, identified as Bacillus firmus, produced a strongly acidic, polysaccharide flocculating agent. The bioflocculant is thermo-stable and 48% of its activity remains after heating at 100degreesC for 50 min. It acts on both inorganic and organic suspensions such as kaolin, activated carbon, pigments and yeast, and its flocculating activity with kaolin suspensions is stimulated by Ca2+, Mg2+ and Fe2+. The bioflocculant was purified to homogeneity by ethanol and cetylpyridinium chloride precipitation. It consists of glucose, fructose, mannose, galactose in a molar ratio of 12.1:5.7:3.1:1 with an approximate molecular size of 2 x 10(6) Da.