Enlargement of Sewage Treatment Plants for Nitrification by Use of Subsequent Rotating Biological Contactors

The surface-specific nitrification performance of Rotating Biological Contactors (RBC) has been improved considerably by the use of new techniques. Maximum nitrification rates of 3.3 g/m2×d (10 °C) were achieved, which cannot be approached with any other known procedure. This high oxidation efficiency is achieved with Rotating Biological Contactors by using two new measures:A large degree of separation of carbon degradation and nitrogen oxidation through filtration of the waste water before the subsequent nitrifying RBC stage, whereby the environmental conditions for the nitrifying bacteria are improved, especially in respect of an optimised supply of oxygen.Periodic reversal of the direction of flow in the RBC stage which is constructed as a cascade. This measure allows the attainment of a uniform thickness of nitrifying bacteria growth in all the compartments, which has a particularly advantageous effect in the case of unavoidable surges in load. Because of the low production of excess sludge in the nitrification stage, a subsequent stage for separating solids is not necessary. In this paper experiences with the upgrading of a full scale rotating biological contactor plant and the measuring results from an enlarged oxidation pond installation are summarized.