Sludgeless oxidative biological purification process

Claim 1

A substantially sludgeless process for oxidative biological purification of 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 a fluidized state aerobic activated 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 3 , at such a rate that space loads of COD 4-50 kg/m 3 day are achieved while continuously and completely separating purified waste water leaving the oxidation space from said attached aerobic activated biomass, the improvement comprising that the waste water is purified with an aerobic activated biomass attached to said insoluble carrier particles under conditions of considerable stirring motions imparted to the fluidized-bed while, minimizing surplus formation of aerobic activated biamass 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 degassing the purified waste water leaving the oxidation space in a separator placed above the oxidation space, while separating by gravity the solids, which are the biomass attached carrier particles, from the purified waste water and accomplishing the return of all the separated solids into the oxidation space by means of recycling by gravity forces alone and finally removing the purified waste water from the separator, wherein to prevent surplus formation of aerobic activated biomass and to exert at the same time adequate control of the pH in the oxidation space with the help of a sufficiently strong natural bicarbonate-carbon dioxide buffer formed only by oxidative microbiological carbon dioxide production from organic compounds of the waste water to be treated, the residence time of the waste water to be treated in the oxidation space is balanced to consume at least one gram of oxygen for each gram of COD converted, and the air-flow rate is maintained so that off-gas from the separator contains at least 5% by volume of oxygen and 1 to 15% dry volume of carbon dioxide.