Short-term effect of ammonia concentration and salinity on activity of ammonia oxidizing bacteria

Abstract

A continuously aerated SHARON (single reactor high activity ammonia removal over nitrite) system has been operated to achieve partial nitritation. Two sets of batch experiments were carried out to study the effect of ammonia concentration and salinity on the activity of ammonia-oxidizing bacteria (AOB). Activity of AOB raised as free ammonia concentration was increased reaching its maximum value at 4.5 mg NH3-N l(-1). The half saturation constant for free ammonia was determined (K(NH3)=0.32 mg NH3-N l(-1)). Activity decreased at TAN (total ammonium-nitrogen) concentration over 2,000 mg NH4-N l(-1). No free ammonia inhibition was detected. The effect of salinity was studied by adding different concentrations of different salts to the biomass. No significant differences were observed between the experiments carried out with a salt containing or not containing NH4. These results support that AOB are inhibited by salinity, not by free ammonia. A mathematical expression to represent this inhibition is proposed. To compare substrate affinity and salinity inhibitory effect on different AOB populations, similar experiments were carried out with biomass from a biological nutrient removal pilot plant. The AOB activity reached its maximum value at 0.008 mg NH3-N l(-1) and decreased at TAN concentration over 400 mg NH4-N l(-1). These differences can be explained by the different AOB predominating species: Nitrosomonas europaea and N. eutropha in the SHARON biomass and Nitrosomonas oligotropha in the pilot plant.

Effect of pH and nitrite concentration on nitrite oxidation rate

“…In order to avoid substrate limitation, the same ammonium concentration (1000 mg NH 4 -N L -1 ) was added in each experiment. According to previous experimental results (Claros et al, 2010) this ammonium concentration assures that the maximum AOB activity is reached.…”

“…Hybridized cells were enumerated using an automated bacteria quantification software (Borrás, 2008). Further information can be found elsewhere (Claros et al, 2010).…”

“…The AOB activity reduction at pH values above the optimum pH is due to the high pH values reached, since it cannot be attributed neither to low substrate concentrations (free ammonia concentration increased as the pH increased along the experiment) nor to high FNA concentrations (FNA concentration decreased due to the pH increment). FA inhibition is not considered since previous experimental results (Claros et al, 2010) showed that salinity and not FA concentrations was responsible for the reduction in the AOB activity. The AOB activity reduction observed at high pH values is not due to salinity as it is the same along each experiment.…”

“…Nitrosomonas eutropha and Nitrosomonas europaea have been identified as the most abundant species in the nitritation process from high ammonia concentration streams. This abundance may be consequence of their tolerance to both high salinity (Claros et al, 2010) and high nitrite concentrations (Beaumont et al 2002). However, the bacterial acclimation could play an important role (Ganigué et al, 2007).…”

Modelación matemática del proceso de nitrificación en dos etapas. Desarrollo de metodologías de calibración del modelo para un reactor SHARON y un proceso de fangos activados

“…El efecto de inhibición por parte del HNO 2 sobre las bacterias amonioxidantes es mayor a pH más bajos y es limitado a pH altos (a una concentración de nitrito de 300 mg/l la concentración de HNO 2 oscila desde 0.52 a 0.00525 mg/l a pH entre 6.0 y 8.0) (Hellinga et al, 1998). Aunque hay diversos estudios donde se considera la inhibición de las bacterias por las altas concentraciones de NH 3 , otros determinaron que la inhibición por salinidad es más importante que la propia concentración del sustrato (Claros et al, 2010).…”