VOLYMBEHOV VID KVÄVERENING / Nitrogen Reduction – Volume Demand
Because of the slow growth of the nitrification bacteria at low temperature, nitrogen reduction normally requires long hydraulic retention times during winter time. Important for the nitrification process is the aerated sludge age. Factors influencing the sludge age are aerated volume, mixed liquid suspended solids concentration, organic load and sludge yield. In an existing plant you can not easily expand the volume and it is difficult to decrease the load. But you can increase the suspended solid concentration by running the biological step with the contact stabilisation process. At the Käppala treatment plant this is easily achieved. With contact stabilisation you can either choose to have the same sludge age and thereby lower the suspended solids concentration in the water to the sedimentation tanks. Or you can increase the sludge age by allowing the concentration in the contact zone to remain at the same level as you had in the aeration tank prior to the process change. “Complete abstract not presented.”