Effect of pH and HNO2 concentration on the activity of ammonia-oxidizing bacteria in a partial nitritation reactor

Abstract

Ammonia oxidizing bacteria (AOB) are very sensitive to environmental conditions and WWTP operational parameters. One of the most important factors that affect their activity is the pH. Its effect is associated to: NH 3 /NH 4 + and HNO 2 /NO 2 -chemical equilibriums and biological reactions rate. The aim of this study was to quantify and model the effect of pH and free nitrous acid concentration on the activity of the AOB present in a lab-scale partial nitritation reactor. For this purpose, two sets of batch experiments were carried out using biomass from this reactor. FISH analysis disclosed that Nitrosomona eutropha and Nitrosomona europaea species were dominant in the partial nitritation reactor (>94%). The experimental results showed that free nitrous acid inhibits the AOB activity. This inhibition was properly modeled by the non-competitive inhibition function and the half inhibition constant value was determined as 1.32 mg HNO 2 -N L -1 . The optimal pH for these AOB was found to be in the range 7.4-7.8. The pH inhibitory effect was stronger at high pH values than at low pH values. Therefore, an asymmetric inhibition function was proposed to represent the pH effect on these bacteria. A combination of two sigmoidal functions was able to reproduce the experimental results obtained.

Modeling the low pH limit of Nitrosomonas eutropha in high-strength nitrogen wastewaters

“…A direct pH term was only required at pH values below pH 6 in our simulations. This finding is in contrast with other studies for high strength nitrogen wastewaters, where sigmoidal or bell-shaped pH terms have been proposed (Antoniou et al, 1990;Claros et al, 2013;Jubany, 2007;Van Hulle et al, 2007). The pH terms in the latter studies decrease the rate of ammonia oxidation strongly between pH 7 and 6.…”

“…To investigate the influence of pH within a range of 5 to 9 and 6 to 9 respectively, Van Hulle et al (2007) and Claros et al (2013) used solutions with total ammonia concentrations between 500 and 1100 mgN$L À1 . It was assumed that this was sufficient to prevent any limitation of NH 3 .…”

Shortcut nitrification/partial nitritation start-up for reject water treatment in a SBR

“…pH can be crucial parameter in nitrification process control, as hydrogen ions concentration has impact on nitrifiers enzyme activity [16]. It is generally accepted that optimal pH range for AOB and NOB are 8.2-0.3 and 7.9-0.4 respectively [17].…”

“…Different approaches on shortcut nitrification/PN were presented in literature, are mostly connected with FA [20][21][22] rather than FNA [16,23] as the selective factor.…”

Estudio Del Proceso De Nitrificación Y Desnitrificación Vía Nitrito Para El Tratamiento Biológico De Corrientes De Agua Residual Con Alta Carga De Nitrógeno Amoniacal

“…El efecto del pH se representó mediante la función asimétrica representada en la Ecuación 4.6, la cual permite ajustar de manera independiente ambos lados del pH óptimo (Claros et al, 2011). En esta expresión las constantes K IH y K H indican el pH al que se alcanza la mitad de la velocidad máxima de crecimiento, mientras que las constantes A H y A IH permiten ajustar la pendiente de la curva de inhibición a ambos lados del pH óptimo.…”