To perform the removal of a metal along with the removal of org. substance from wastewater and the deodorizing of wastewater by bringing Bacillus sereus into contact with wastewater.

Bacillus sereus is brought into contact with wastewater. Bacillus sereus to be used is well grown on any general nutrient culture medium and well propagated pref. at about 15-45°C. Bacillus sereus is pref. immobilized on a carrier as a microorganism group and used as a carrier immobilized microorganism group made easy to handle. As the carrier, a porous material having open vent pores such as porous ceramic or porous plastic is especially pref. The diameter of the vent pores of the porous material is pref. about 2-10 μm. As the carrier, a particulate material with a mean particle size of 2 mm or less, especially, about 50 μm-1 mm is pref. The microorganism group is supported by mixing the carrier with a microorganism group dispersion and drying the resulting mixture but the microorganism group may be directly cultured on the carrier.