Characterization of functional microorganism groups and substrate in activated sludge and wastewater by AUR, NUR and OUR

G. Holm Kristensen, P. Elberg Jørgensen, Mogens Henze

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Activated sludge functional microorganism groups: nitrifiers, denitrifiers and heterotrophs, were characterized through determinations of maximum specific utilization rates of ammonia (AUR) nitrate (NUR) and oxygen (OUR). Characterizations of the functional groups were done on activated sludges from a pilot plant and from full-scale plants. Influent wastewater covered a wide spectrum, including raw wastewater, primary wastewater and chemically pretreated wastewater. AUR determinations showed significant variation with influent COD:N ratio, and good agreement was found with expected rates from mathematical simulations. For increased contents of particles in influent wastewaters a decreased maximum OUR was found, while maximum NUR was slightly increased or not affected. Based on NUR and OUR the fraction of denitrifiers to heterotrophs was estimated in the range of 41-73% in nitrogen removal sludges. The results indicated that influent biomass is of significance for the obtained fraction of denitrifiers to heterotrophs. For a separate nitrification stage activated sludge without denitrification a fraction of denitrifiers of 15-20% was found. The results of endogenous NUR and OUR determinations indicated that hydrolysis of activated sludge COD takes place with the same rate under anoxic and aerobic process conditions.
Original languageEnglish
JournalWater Science and Technology
Issue number6
Pages (from-to)43-57
Publication statusPublished - 1992


  • Activated sludge
  • nitrifiers
  • denitrifiers
  • heterotrophs
  • nitrification rate
  • nitrate respiration rate
  • oxygen respiration rate
  • viable biomass
  • wastewater characerization

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