TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The microorganism after selection is again cultivated in presence of organophosphorus compound. The organophosphorus compound is organic phosphoric acid compound. The concentration of organophosphorus compound during culture process is set to 50-100 ppm. The activated sludge containing microorganism and/or processing material of microorganism is contacted with water.    TECHNOLOGY FOCUS - BIOLOGY - Preferred Microorganism: The microorganism is Zoogloea ramigera. EXAMPLE - A culture medium (1) containing potassium chloride (0.2 g/l), magnesium sulfate heptahydride (0.2 g/l), ammonium sulfate (0.5 g/l), ammonium citrate iron (1 mg/l), calcium chloride dihydride (2 mg/l), glucose (0.3 g/l) and organophosphorus compound (50 mg/l) and a culture medium (2) containing acetic acid (40 mg/l), ethanol (47 mg/l), magnesium sulfate (0.2 g/l), calcium chloride dihydride (0.2 g/l), sodium hydrogencarbonate (0.03 g/l), ammonium sulfate (0.12 g/l), sodium nitrate (2.6 mg/l), salt solution (1 ml/l), vitamin solution (1 ml/l) and organophosphorus compound (50 mg/l) were prepared. 9.5 ml of each of culture solution was transferred to a test tube. 0.5 ml of activated sludge of sewage was added and centrifuged. The deposit was added to culture medium and growth of microorganism was carried out. The culture deposit was inoculated to a culture medium of same composition and the growth of microorganism was continued. The culture medium was transferred to a plate and formation of colony of the microorganism was confirmed. The strain containing microorganism with decomposition ability of organophosphorus compound was chosen and separated and was found to be Zoogloea ramigera. The microorganism was cultivated in a culture medium and activated sludge was added and centrifuged. The decomposing ability of organophosphorus compound in the supernatant liquid was examined. The organophosphorus compound was decomposed by the sludge from 3-7 days, indicating excellent decomposing ability of sludge containing microorganism.