The minimum temperature in an activated sludge process is 5 C. The process needs to nitrify all year round. In the process WAS is taken from the RAS flow. What is the WAS flow rate (m3/d) when the influent flow rate is 10 000 m3/d and hydraulic retention time is 6h? The SS concentration in RAS can be assumed to be twice the MLSS in the aeration basin. What is the total SRT in the process when a denitrification zone of 40% of the aeration volume is added?