title: NOx monitoring of a simultaneous nitrifying-denitrifying (SND) activated sludge plant at different oxidation reduction potentials.
abstract: 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 220-240mV ORP (given as E(h)) with corresponding maximal NO(G) emissions rates of 0.9microgg(-1)VSSh(-1). The maximal emission rates of NO(2G) (0.2microgg(-1)VSSh(-1)) were reached at the same ORP level and the NO(2G) emissions correlated to the nitrite accumulation in the activated sludge up to 5mgl(-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.
authors.affiliation: Department of Water-Atmosphere-Environment, Institute of Sanitary Engineering and Water Pollution Control, University of Natural Resources and Applied Life Sciences Vienna, Muthgasse 18, 1190 Vienna, Austria.
authors.forename: Norbert
authors.initials: N
authors.lastname: Weissenbacher
authors.forename: Christian
authors.initials: C
authors.lastname: Loderer
authors.forename: Katharina
authors.initials: K
authors.lastname: Lenz
authors.forename: Susanne N
authors.initials: SN
authors.lastname: Mahnik
authors.forename: Bernhard
authors.initials: B
authors.lastname: Wett
authors.forename: Maria
authors.initials: M
authors.lastname: Fuerhacker
mesh_terms: D001420:Bacteria, Aerobic / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000378:metabolism; D019149:Bioreactors; D009569:Nitric Oxide / Q000032:analysis / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D009609:Nitrous Oxide / Q000032:analysis / Q000378:metabolism*; D010084:Oxidation-Reduction; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology; D018508:Water Purification / Q000379:methods*
chemical_list: D012722:Sewage; D009569:Nitric Oxide; D009609:Nitrous Oxide; D009584:Nitrogen