Method for biological cleaning of wastewater
A method for biological purification of wastewater is disclosed, wherein the wastewater is purified in a biofilm process followed by an activated sludge process. The biological degradation in the biofilm process is performed under limitation of one of the nutrient salts nitrogen or phosphorous, and the surplus sludge from the biofilm process is allowed to pass to the activated sludge process.
1. 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.
2. The method according to claim 1 , wherein the biofilm process is operated at a load within the interval from 2 to 20 kg BOD 5 per m 3 process volume and 24 hours, preferably within the interval from 3 to 15 kg BOD 5 per m 3 process volume and 24 hours, particularly within the interval from 4 to 10 kg BOD 5 per m 3 process volume and 24 hours.
3. The method according to claim 1 , wherein the biofilm process is arranged such that the carrier material for microbial growth in the process is kept completely or partially in suspension and movement by the supply of air to the process.
4. The method according to claim 1 , wherein a partial flow of outgoing wastewater from the separation step of the active sludge process is returned to the biofilm process.
5. The method according to claim 1 , wherein further biologically available nitrogen and/or phosphorus is dosed directly to the activated sludge process.
6. The method according to claim 1 , wherein the biofilm process is performed in at least two steps.