NOx monitoring of a simultaneous nitrifying-denitrifying (SND) activated sludge plant at different oxidation reduction potentials

Water Res. 2007 Jan;41(2):397-405. doi: 10.1016/j.watres.2006.10.034. Epub 2006 Dec 12.

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.

MeSH terms

  • Bacteria, Aerobic / metabolism
  • Bacteria, Anaerobic / metabolism
  • Bioreactors
  • Nitric Oxide / analysis
  • Nitric Oxide / metabolism*
  • Nitrogen / metabolism*
  • Nitrous Oxide / analysis
  • Nitrous Oxide / metabolism*
  • Oxidation-Reduction
  • Sewage / chemistry*
  • Sewage / microbiology
  • Water Purification / methods*

Substances

  • Sewage
  • Nitric Oxide
  • Nitrous Oxide
  • Nitrogen