INFLUENCE OF PH OVER NITRIFYING BIOFILM ACTIVITY IN SUBMERGED BIOFILTERS

The influence of pH over nitrification in submerged biofilters has bee n studied through the observation of three pH effects over the nitrify ing biofilm: activation-deactivation, substrate limitation, and free a mmonia inhibition. Within a pH range of 5.0-9.0, a pH increase of one unit produce a 13% increase on the nitrification efficiency. A stoichi ometry of 7.1 mg CaCO3/mg N was measured for the process, which became alkalinity limited below pH 5.0. The highest activity of ammonium oxi dizers and the highest values of volatile attached solids (VAS) in the filter were obtained at pH 8.2. The concentration of volatile attache d solids (VAS) was regulated by free ammonia inhibition, substrate lim itation (NH4+ concentration), and reactor hydrodynamics. Inhibition by free ammonia controlled bacteria activity at pH greater than 7.5, obs erving an increase of microorganisms concentration in the filter as a specific free ammonia concentration (mg NH3free-N gVAS(-1)) decreased. A nitrite accumulation of up to 80-90% was obtained for specific inhi bitory concentrations greater than 1.5 mg NH3free-N gVAS(-1) resulting from the selective inhibition of nitrite oxidizers. (C) 1997 Elsevier Science Ltd.