Free ammonia and free nitrous acid inhibition on the anabolic and catabolic processes of Nitrosomonas and Nitrobacter

Abstract

The inhibitory effects of free ammonia (FA) and free nitrous acid (FNA) on the catabolic and anabolic processes of Nitrosomonas and Nitrobacter were investigated using a method that allows decoupling the growth and energy generation processes. Lab-scale sequencing batch reactors (SBRs) were operated for the enrichment of Nitrosomonas and Nitrobacter. Fluorescent In-Situ Hybridization (FISH) analysis showed that the reactors were 82% and 73% enriched with Nitrosomonas and Nitrobacter, respectively. Batch tests were carried out to measure the oxygen uptake rate (OUR) by the enriched cultures at various FA and FNA levels, in the presence (OUR with CO2 ) or absence (OUR without CO2) of inorganic carbon (CO2, HCO*3 and CO 2*3). FA up to 16.0 mgNH3-N.L(-1) was not found to have any inhibitory effect on either the catabolic or anabolic processes of the Nitrosomonas culture, but both these processes were inhibited by FNA. While an FNA level of 0.40-0.63 mgHNO2-N.L(-1) inhibited the energy production capability of Nitrosomonas by 50%, the growth process of the culture was completely inhibited by FNA at a concentration of 0.40 mgHNO2-N.L(-1). Both FA and FNA were found to have strong inhibition on the anabolic processes of Nitrobacter, but with limited inhibitory effects on the catabolism of this culture. The biosynthesis of Nitrobacter was totally inhibited at an FA level of 6.0 mgNH3-N.L(-1) (or above) or an FNA level of 0.02 mgHNO2-N.L(-1) (or above). At the same level of FA, the energy production capability of Nitrobacter was only inhibited by 12%, whereas an FNA level of up to 0.024 mgHNO2-N.L(-1) did not show any inhibition on the energy production of Nitrobacter. Further, these inhibitory effects appears to be much stronger on Nitrobacter than on Nitrosomonas, supporting that FA and FNA inhibition may play a major role in the elimination of nitrite oxidizing bacteria in processes treating wastewater containing a high level of nitrogen.

Comparison of Partial and Full Nitrification Processes Applied for Treating High-Strength Nitrogen Wastewaters: Microbial Ecology through Nitrous Oxide Production

“…The lack of detection of Nitrospira spp. related NOB during partial nitrification is consistent with previous studies 18,30,31 and was likely due to the propensity of Nitrospira spp. to preferentially grow at lower nitrite concentrations.…”

Landfill Leachate Nutrient Removal Using Intermittent Aeration

“…Nitrite accumulation was significantly higher than nitrate at day 1 and the NO 2 − -N/NO x -N ratio increased gradually from 0.2 to 0.7 during the start-up period at day 1. The inhibition of ammonium and nitrite oxidation by free ammonia and nitrous acid is well known Vadivelu et al 2007). The inhibitory effects of substrate concentration, among other factors, such as pH, T, DO and SRT, are strong and complex, due to unionization phenomena.…”

“…Moreover, Bae et al (2001) reported that nitrite accumulation occurred at initial free ammonia concentration of 4.7 mg/L, giving a high NO 2 − /NO X ratio (up to 77 %) in a batch reactor. On the other hand, the works of Vadivelu et al (2007) indicated that nitrite oxidation could be selectively inhibited by free nitrous acid. Nitrite oxidation could be affected more than ammonium oxidation by free ammonia, resulting in accelerating nitrite accumulation in a strong nitrogenous environment.…”

Effect of Aeration Rates on Removals of Organic Carbon and Nitrogen in Small Onsite Wastewater Treatment System (Johkasou)

“…These factors included higher free ammonia [4]- [6], hydraulic retention time (HRT) [7], [8], dissolve oxygen (DO) concentration and inhibitor [9]. However, the efficiency of biological nitrogen removal can be improved by maintaining and monitoring the ORP, pH and DO in the nitrification-denitrification process [10].…”