TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: A step is provided for supplying nitrogen at reduced state to the material for treatment. The biological treatment is conducted in an aerobic atmosphere, particularly with maintenance of the biological activity of the first microorganism, followed by anaerobic treatment in an anaerobic atmosphere in which a second microorganism is applied for carrying reduction of the nitrogen at oxidized state to effect removal of the chlorine-containing organic compound from the material. Also included are steps for adding the first microorganism, oxygen, second microorganism, and nutrient and organic carbon source for the second microorganism, as well as for decomposing the chlorine-containing compound, for stopping oxygen supply to provide anaerobic atmosphere, and for mixing the material for treatment. The first and/or second microorganisms are used in the form of a dehydrated cake with some water removed, or as a freeze-dried powder, particularly as a slurry with the material for treatment. A step is provided for adjusting pH of the first microorganism and material for treatment that contains nitrogen at reduced state, and/or a desalting step to reduce the salt concentration in the material to not more than 4%. The amount of nitrogen at reduced state to be added during the process is 0.01-10 g-N. When carrying out the anaerobic treatment, the treated material is kept at not more than 15degreesC.Preferred Apparatus: The apparatus is equipped with components and parts to provide the nitrogen at reduced state, various microorganisms, oxygen and nutrients to carry out aerobic and anaerobic reactions, to cut off oxygen supply, to form slurry, to adjust pH and to desalt the material for treatment. EXAMPLE - Leachate from refuse was mixed with soil containing Nitrosomonas nitrification bacteria with stirring in a stainless steel reactor as a suspension of 8.1 g/l and in salt concentration of 1.2%. Supplied were 7.7 g/day of urea and sodium hydroxide for adjusting pH to 7. The reaction was conducted at 18-20degreesC with nitrogen volume load of 0.2 kg-Ngm3/day. Dioxins e.g. polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans were checked; the amounts reduced from 110-370 pg/g to 16-60 pg/g.