NO x monitoring of a simultaneous nitrifying–denitrifying (SND) activated sludge plant at different oxidation reduction potentials

• Published in: Water research (Oxford) Vol. 41; no. 2; pp. 397 - 405
• Main Authors: Weissenbacher, Norbert, Loderer, Christian, Lenz, Katharina, Mahnik, Susanne N., Wett, Bernhard, Fuerhacker, Maria
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2007
• Subjects: Activated sludge; NO x monitoring; ORP control; Simultaneous nitrification–denitrification; SND; Activated sludge; NO x monitoring; ORP control; SND; Simultaneous nitrification–denitrification
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2006.10.034

Simultaneous nitrification–denitrification (SND) allows biological nitrogen removal in a single reactor without separation of the two processes in time or space but requires adapted control strategies (anoxic/aerobic conditions). In this study, the formation of gaseous nitric oxide (NO G) and nitrogen dioxide (NO 2G) was monitored for SND in relation to the oxidation-reduction potential (ORP) and nitrogen removal in a lab batch reactor and a pilot membrane bio-reactor (MBR). In addition hospital wastewater (COD/N tot>6:1) was treated on site for 1 year. The highest total nitrogen removal rates of max 90% were reached at 220–240 mV ORP (given as E h) with corresponding maximal NO G emissions rates of 0.9 μg g −1 VSS h −1. The maximal emission rates of NO 2G (0.2 μg g −1 VSS h −1) were reached at the same ORP level and the NO 2G emissions correlated to the nitrite accumulation in the activated sludge up to 5 mg l −1 NO 2L-N. It was shown that this correlation was due to biological production and not due to pH-dependent chemical conversion. Therefore, NO 2G can be used as additional control loop for ORP-controlled SND systems to avoid the inhibition of denitrification and high nitrite concentrations in the plant effluent.