TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Process: The culture is obtained by cultivating in a thiamin containing medium, having thiamin concentration of 2-2000mu g/l. The microorganism which has APR-3 producing ability is a composite microorganism containing one or more species, preferably of bacteria. The water treatment process involves activated sludge processing of water. The treated water and activated sludge are separated. The increase in bulk of activated sludge is prevented by the flocculant. The pH of activated sludge is maintained at 7-9. Preferred Microorganism: The microorganism having APR-3 producing ability is Brucella, Xanthomonas, Acinetobacter, Comamonas, Salmonella, Aureobacterium, Cellulomonas or Agrobacterium. Preferably, the microorganism is composite microorganism, at least one specie of the bacteria belonging to Cellulomonas cellulance or Agrobacterium tumefaciens. Preferred Flocculant: The flocculant contains one or more kinds of cationic mineral salts. SPECIFIC MICROORGANISMS - The microorganism having APR-3 producing ability is Cellulomonas cellulance KYM-7 strain (FERM P-11339) or Agrobacterium tumefaciens KYM-8 strain (FERM P-16806) (claimed). The microorganisms are also chosen from Brucella sp. KYM-1 strain (FERM P-11333), Stenotrophomonas or Xanthomonas KYM-2 strain (FERM P-11334), Acinetobacter KYM-3 strain (FERM P-11335), Comamonas testosteroni KYM-4 strain (FERM P-11336), Salmonella sp. KYM-5 strain (FERM P-11337) or Aureobacterium sp. KYM-6 strain (FERM P-11338) (claimed).    EXAMPLE - A culture medium containing (in weight percent) starch (1), K2HPO4 (0.5), KH2PO4 (0.2), MgSO4.7H2O (0.02), (NH4)2 SO4 (0.05), yeast extract (0.05), thiamine hydrochloride (200mu g/l) and water, at pH 7, was used for culturing microbe R-3 (mixed microbes containing KYM-1, KYM-4, KYM-5, KYM-7 and KYM-8 strains of bacteria) for 5 days at 30degreesC in broth agar flat plate medium containing 0.1 mg/l of thiamin hydrochloride. 60 ml of culture solution was added to 3 l of culture medium. The degree of growth (measured by turbidity) of the culture was 16.5, kaolin aggregation activity was 277, and viscosity was 1200 cP. Oil and water separability for APR-3 was very high (93%). Microbial cells were removed by centrifugation and concentrated to precipitate fibrous APR-3. The precipitate was dried and 9.2 g of crude APR-3 (starch yield 30.5) was obtained. The crude APR-3 (500 mg) in water was mixed with 50 ml of 2% cetyl pyridium chloride (CPC) solution, and precipitate of composite of APR-3 and CPC, was formed. From the composite, 380 mg (98%) of pure APR-3 was obtained (2 mg/ml from culture solution of R-3 microbe). The APR-3 was analyzed and it was found that the novel medium had: (i) sugar content (phenol-sulfuric acid method): 64+/-2 weight %; (ii) amino sugar: undetectable (Elson-Morgan method); (iii) Uronic acid: undetectable (carbazole-sulfuric acid method); (iv) protein: undetectable (ninhydrine method);(v) elemental analysis: C 40+/-2%, H 6+/-1% and trace amounts of N, P, S; (vi) the composition (molar ratio) of sugar and organic acid: 5.6+/-0.1 mol glucose for 1 mol of galactose, 0.6+/- 0.1 mol of succinic acid and 2.5+/-0.1 mol of pyruvic acid for 1 mol of galactose; (vii) molecular weight: 2x106; (viii) viscosity (by rotational viscometer, 25degreesC, rotation speed 3-60 rpm): Pseudo-plastics type flow was characterized when APR-3 was taken in xanthan gum, high viscosity was observed; (ix) solubility: soluble in water, easily soluble in alkali, insoluble in methanol and acetone; (x) specific rotation: -17 to -15degrees. The properties obtained were unique for the novel polymeric flocculant.