Innovative Control Strategies for the Partial Nitritation/Anammox Wastewater Treatment Process

Sammanfattning: The project undertaken in this thesis was proposed by IVL Swedish Environmental Research Institute and performed at their R&D facility Hammarby Sjöstadsverk as a part of the EU funded research project R3 Water. A single stage partial nitritation/Anammox system in a moving bed biofilm reactor (MBBR) was controlled using oxidation reduction potential (ORP) in order to evaluate its utility as control parameter. The system was operated in 10 periods under a combination of several different pH levels (7, 7.5, 8), nitrogen loads (1, 2.5, 4 gN/m2/d), and ORP (-70, 0, 70 mV) values following a 2n full factorial design. The results were then interpreted using the design of experiment software MODDE in order to find the optimal operating conditions. Stable operation and acceptable levels of nitrogen removal (>80%) were achieved for three periods where the common factor was an ORP value of 70 mV. The highest nitrogen removal rate (83.7%) was found when the test conditions were pH 8, nitrogen load 1 gN/m2/d, and ORP 70 mV. The economic performance of each period was also evaluated and it was found that the optimal point, in terms of aeration and of the three periods with sufficient removal efficiencies, was the same as the optimal removal conditions except with a pH of 7. The resulting cost was 0.0046 SEK/gN removed. A secondary test was performed in order to directly compare the performance of ORP with dissolved oxygen (DO) as a control parameter. It was found that DO significantly outperformed ORP under identical test conditions, yielding a higher nitrogen removal rate (78.2% vs. 65.3%) as well as significantly less aeration energy.