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Abstract

An oxidative biological purification process for waste water in a fluidized-bed reactor at a pH between 5 and 8 in the oxidation space comprising passing waste water upwards through an air-sparged oxidation space containing aerobic biomass attached to insoluble carrier particles of a size of 0.1 to 2 mm with a specific gravity of 2 to 5 g/cm.sup.3 at such a rate that space loads of COD of 4-50 kg/m.sup.3 day are achieved while continuously and completely separating purified waste water leaving the oxidation space from said attached aerobic biomass, whereby the aerobic biomass prevails to at least a very substantial extent in a state of attachment to said carrier particles, undue surplus formation of said sludge being minimized by continuous control of the residence time of the waste water to be treated in the oxidation space between the limits of 0.3 to 20 hours, and at least all attached aerobic biomass is recycled to the oxidation space by way of settling. Preferred embodiments include placing of a relatively smaller settling tank above the oxidation space, the use of sand as carrier material, gas and liquid flows being the only sources for stirring applied continuously, and purification at a temperature of 30.degree.-50.degree. C. The process gives a reliable waste water purification at a low level of surveillance even when considerable variations occur in the supply of COD and in the pH of the waste water introduced.

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