Fremgangsmåde til behandling af spildevand

摘要

The invention relates to a method for the treatment of (raw) sewage in a package plant consisting of three bioreactors in series. The treatment is being carried out using three types of biomass. In a first step (3,4) phosphate is removed by biological means and, at the same time, the chemical and biological oxygen demand is lowered in a highly loaded active sludge system, in a second step (10) a nitrification is carried out, ammonium being converted to nitrate, and in a third step a denitrification (12) is carried out using a carbon source. In the denitrification step acidified surplus sludge from the P-removing step can also be used instead of an external carbon source. The nitrifying and denitrifying bioreactors are both fixed film processes. The thickness of the biofilm on the support material in the nitrifying bioreactor can be influenced by adjusting the aeration system or by adjusting the hydraulic loading. In the denitrifying bioreactor the thickness of the biofilm can be adjusted by raising the shear by means of raising the superficial velocity in the support material. The system according to the invention makes possible effective treatment of raw sewage in a highly loaded system resulting in the far-reaching removal of COD, nitrogen and phosphate. The process can be operated in an alternative mode, where the nitrifying and denitrifying bioreactors are exchanged; first bioreactor: biological-P-removal and simultaneous reduction of COD, second bioreactor: denitrification and third bioreactor: nitrification. The effluent of the nitrifying bioreactor is recirculated to the denitrifying bioreactor. The first step is carried out in a plug flow bioreactor with an anaerobic and an aerobic zone. By using an intermediate settling tank (5) between the first and the second step, it is possible to discharge phosphate-rich surplus sludge. The mixing in the nitrifying step is advantageously maintained by aeration under the packages of support material. Mixing in the denitrifying step is accomplished by means of a propellor.