Advanced Control System to Reduce N2O Emission and Improve Performance of an SBR Treating N-Rich Effluent Via Nitrite Pathway
Abstract:N-removal via the nitrite pathway is an attractive process to treat N-rich effluent such as anaerobic digestion liquors. Costs saving could be achieved due to less oxygen and carbon substrate requirement. However it has been reported that under certain operating conditions these nitrite pathway processes could generate large amount of N2O which is a strong greenhouse gas and therefore off-set the promising energy and costs savings. In this study, a new nitrite pathway SBR process called ANITA™ Shunt was developed to reduce the N2O emission. A 500L SBR Pilot was operated for 18 months to treat digested sludge filtrate, more than 90% of N-removal was achieved via the nitrite pathway and N2O emission was less than 0.7% of the N-removed. The patented SBR cycle control system is based on the use of free nitrous acid (FNA) concentration set-point, calculated in real time by using pH, temperature and NO2 − on-line measurement, in order to stop the aeration phase and limit the N2O emission. This works clearly demonstrated that N2O emission during nitrification stage under low DO condition by AOB is not directly linked to high nitrite level as reported in the literature but mainly to FNA level.
Document Type: Research Article
Publication date: 2011-01-01
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