INFLUENCE OF SUBSTRATE CONCENTRATION ON THE GROWTH AND ACTIVITY OF A NITRIFYING BIOFILM IN A SUBMERGED BIOFILTER

The influence of substrate concentration over the concentration and ac tivity of the nitrifying biofilm in an Up-flow Biological Aerated Filt er (UBAF) is presented. Two effects, nutrition and inhibition, were ob served on the biofilm activity and both were respectively associated t o the cationic and neutral form of the substrate. The nutritional effe ct, of the substrate was expressed and quantified as the specific ammo nium concentration as g NH4+-N kg VAS(-1) (Volatile Attached Solids), and the inhibition as the specific free ammonia concentration g NH3-N kg VAS(-1). Ammonium concentration ranged between 50 and 150 g NH4+-N m(-3). When surpassing a specific ammonium concentration of 3 g NH3-N kg VAS(-1) in the system the specific activity of ammonia and nitrite oxidizers decreased although the biomass concentration remained consta nt. In the other way when surpassing a free ammonia concentration of 0 .5 g NH3-N kg VAS(-1) the biofilm concentration decreased and ammonia oxidizers showed greater activity than nitrite oxidizers occurring nit rite accumulations in the system up to values of 90%.