Single-disc investigations on nitrogen removal of higher loads in sequencing batch and continuously operated RDR systems

Abstract

Nitrification of ammonium-rich synthetic wastewater was studied in a continuously operated rotating disc reactor (RDR) with additional aeration. For a wastewater with 500 mg L−1 NH4−N a nearly complete oxidation to nitrate could be demonstrated for a hydraulic residence time of 27 h (HRT). The reactor was nearly completely mixed. Nevertheless, the biofilm covering the first discs was remarkably thicker than that of the last discs. In order to study the bioactivity of selected discs, single-disc reactors were used. The determined ammonium oxidation rate was nearly independent of the thickness and location of the disc. In contrast, the nitrite oxidation rate increased from the first to the last discs. Some results from experiments on nitrogen removal in sequencing batch single-disc reactors (SBSDR) are discussed. The SBSDR was operated with 2 phases, a partially submerged phase for nitrification and a completely submerged anoxic phase in which acetate was added for denitrification. It was advantageous to operate without additional aeration and thus produce more nitrite and saving carbon and energy. First results of the treatment of a synthetic wastewater with a C:N ratio of 1 in a 5-phase SBBR process providing 2 nitrification, 2 anoxic and a final aerobic post-treatment phase showed average specific rates.