NOVELTY - Iron bacterium and microorganism support are injected into reaction tank. An acidic waste liquid (11) containing bivalent ferric iron is supplied to tank, and bivalent ferric iron is oxidized. The pH of reaction tank is adjusted to 3-5, and iron hydroxide (III) particles are produced. The sedimentation of slurry containing particles and support is carried out. Slurry is fed to flocculation tank, and a polymer flocculent (21) is added. Floc of iron hydroxide particles is formed. Sedimentation of slurry is carried out, and iron hydroxide particles are recovered.    USE - Recovery of iron material from waste liquid, such as acid wash waste liquid and metal-plating waste liquid of steel plate.    ADVANTAGE - The iron material is economically recovered from waste liquid. The stirring motive power in reaction tank is suppressed. The moisture content of iron-containing dewatered cake is reduced.    DETAILED DESCRIPTION - Iron bacterium and microorganism support containing coke breeze, activated carbon, coal dust, pumice powder and foamed slag are injected into reaction tank. An acidic waste liquid (11) containing bivalent ferric iron is supplied to reaction tank stirred by aeration, and bivalent ferric iron is oxidized to trivalent ferric iron by iron bacterium. The pH of reaction tank is adjusted to 3-5, and iron hydroxide (III) particles are produced. The sedimentation of slurry containing iron hydroxide particles and support is carried out in a sedimentation tank, and settled support is returned to reaction tank. Slurry containing iron hydroxide particles discharged from sedimentation process is fed to flocculation tank, and a polymer flocculent (21) is added. Floc of iron hydroxide particles is formed. Sedimentation of slurry containing floc of iron hydroxide particles is carried out in sedimentation tank, and slurry containing floc of iron hydroxide particles is recovered. Thus, iron material is recovered from waste liquid.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of processing apparatus of iron-containing dewatered cake. (Drawing includes non-English language text)    Wastewater treatment equipment (10)    Acidic waste liquid (11)    Microorganism support (13)    Diffuser (14)    Neutralizing agent (17)    Polymer flocculent (21)