TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: (M1) involves supplying air to the soil to disperse fresh water and/or sea water. The contaminants in soil such as monocyclic and/or polycyclic aromatic hydrocarbons are processed using the microorganisms in contaminated soil, and/or by adding the microorganisms which acclimatized with the contaminant. The wash water of the sludge treated contaminated soil contains the activated-sludge treated water of the ammoniacal liquor produced from coke works.The microorganisms in the contaminated soil and the added microorganisms which are immobilized on a carrier, process the wash water in the reaction tank such as a fixed bed type in which the oxidation reduction potential (ORP) is maintained more than silver/silver chloride composite-electrode reference standard (OmV).An aqueous solution of a cyclodextrin and/or a surfactant is added to the wash water. An iron-type coagulant is also added to the wash water and a cyanide ion is removed by aggregation operation. The wash water is further processed by ozone, ultraviolet radiation or a photocatalyst. The pH of the treated water is adjusted between 6-8.5. EXAMPLE - The contaminated soil was washed with mixed water (sea water: fresh water = 1:1). The fragmenting process was performed and the water was eluted. 100 mg/l of an iron-type coagulant such as ferric chloride was added to the wash water and microorganism inhibitor such as SS component and cyanogen were removed by aggregation operation. The wash water was sent to reaction tank for processing by microorganisms. The hydraulics study-residence time (HRT) of microorganisms reaction-tank which oxidized the wash water hydrocarbon to carbon dioxide by the bacteria carried out the water flow for 24 hours at the beginning.    Reaction tank was of fixed bed type and had a blower for aeration. The evolution number of blower was controlled as the oxidation-reduction potential (ORP) of the reaction tank was maintained more than OmV (silver/silver chloride composite-electrode reference standard). The pH of the reaction tank was maintained between 6-8.5 suitable for growth of microorganisms using dilute sulfuric acid or sodium hydroxide.    The microorganisms were immobilized on a carrier such as carbon fiber. An ozone oxidation apparatus was also installed in the later stage of microorganisms processing. As for the benzene of treated water, HRT of microorganisms reaction tank became 0.5 mg/l less than an efficient standard of 0.1 mg/l under conditions of 24 hours. Total polycyclic aroma genus hydrocarbons (T-PAHs) became 2.5 mg/l. The benzene of final treated water which involved an ozone treatment became 0.01 mg/l and T-PAHs became 1 mg/l.