TEMPERATURE EFFECT ON NITRIFYING BACTERIA ACTIVITY IN BIOFILTERS - ACTIVATION AND FREE AMMONIA INHIBITION

Nitrifying bacteria activity and concentrations depend on specific fre e ammonia concentration (ratio NH3/biomass), that is a function of tem perature, pH, ammonium concentration and nitrifying biomass concentrat ion. So, temperature is a key parameter in the nitrification process p roducing two opposite effects: bacteria activation and free ammonia in hibition. These phenomena are studied in an up-flow biological aerated filter (UBAF) settled by a nitrifying biofilm (measured as Volatile A ttached Solids, VAS). The plug flow allows to disclosure of both effec ts, activation and inhibition. For Nitrosomonas bacteria only an activ ation effect was observed; their activity reaches a maximum at 28-29 d egrees C. For Nitrobacter the free ammonia inhibition prevails against the activation effect for values greater than 1 mg N-NH3/mg VAS allow ing nitrite accumulation of 80%; this inhibition threshold value for n itrifying biofilm is obtained measuring the specific rate of utilizati on of substratum per unit of biomass (mu(max)/Y) by activity test. The knowledge of this threshold in a biofilm process is fundamental in or der to control the nitrite accumulation in nitrifying biofilm reactors .