Patent ID: 6946074

Claim:
A method for biological purification of wastewater wherein the wastewater is purified first in a biofilm process and then in an activated sludge process all surplus biomass from the biofilm process or the main portion thereof is allowed to pass to the activated sludge process, wherein the biological degradation process in the biofilm process is operated under limitation of one of the nutrient salts, nitrogen or phosphorous by the quotient between the amounts of BOD 5 and biologically available nitrogen supplied to the biofilm process. Being kept within the interval from 60:1 to 240:1, preferably within the interval from 80:1 to 180:1, particularly within the interval from 100:1 to 150:1 and/or the quotient between the amounts of BOD 5 and biologically available phosphorus supplied to the biofilm process being kept within the interval from 300:1 to 1200:1, preferably within the interval from 450:1 to 900:1, particularly within the interval from 500:1 to 700:1.