Concurrent nitrite oxidation and aerobic denitrification in activated sludge exposed to volatile fatty acids

Abstract

The goal of this research was to investigate the simultaneous occurrence of nitrification and denitrification by activated sludge exposed to volatile fatty acids (VFAs) during aerobic wastewater treatment using a single-stage reactor. A mixture of VFAs was spiked directly into a continuous-stirred tank reactor (CSTR) to assess subsequent impacts on nitrite removal, nitrate formation, CO(2) fixation, total bacterial density, and dominant nitrite oxidizing bacteria (NOB) concentration (i.e., Nitrospira). The activity of the periplasmic nitrate reductase (NAP) enzyme and the presence of nap gene were also measured. A rapid decrease in the nitrate formation rate (>70% reduction) was measured for activated sludge exposed to VFAs; however, the nitrite removal rate was not reduced. The total bacterial density and Nitrospira concentration remained essentially constant; therefore, the reduction in nitrate formation rate was likely not due to heterotrophic uptake of nitrogen or to a decrease in the dominant NOB population. Additionally, VFA exposure did not impact microbial CO(2) fixation efficiency. The activity of NAP enzyme increased in the presence of VFAs suggesting that nitrate produced as a consequence of nitrite oxidation was likely further reduced to gaseous denitrification products via catalysis by NAP. Little, if any, nitrogen was discharged in the aqueous effluent of the CSTR after exposure to VFAs demonstrating that activated sludge treatment yielded compounds other than those typically produced solely by nitrification.

Combined Enhanced Biological Phosphorus Removal (EBPR) and Nitrite Accumulation for Treating High-strength Wastewater

“…Eilersen et al (1994) reported that acetate acid and propionate acid can inhibit the activity of NOBs but have no impact on AOBs. Delgado et al (2004) and Oguz (2004) found that under the same concentration of VFAs (~600 mg acetate/L), the inhibition of nitrite oxidation was 1.3 times higher than the ammonia oxidation rate. And they also found that with an initial dose of 150 acetic acid mg/L, nitrite oxidation activity was decreased over 45% but ammonia oxidation activity was only decreased around 20%.…”

Iron Robustly Stimulates Simultaneous Nitrification and Denitrification Under Aerobic Conditions

“…The detection of the NapA gene, which encodes enzyme NAP responsible for NO 3 − -N reduction, has often been applied as the proof of aerobic denitrification in mixed liquor samples. 10 The genes NirK and NirS encode the enzyme responsible for reducing NO 2 − -N to NO. It was indicated from Figure 7(b) that the relative quantities of the NapA, NirK, and NirS genes in Sludge-Fe were 2.24-, 6.87-, and 5.45-fold higher than those of Sludge-C, respectively.…”

“…9 Moreover, the detection of NapA gene, which encodes the NAP enzyme, also suggests that aerobic denitrification can occur. 10,11 In this study, the nitrogen species transformations and the corresponding enzymes in SND process are summarized in Figure 1. 12,13 It can be seen from Figure 1 that large amounts of metalloproteins (such as cytochrome and dehydrogenase) and certain functional nitrification and denitrification enzymes (i.e., AMO, NXR, NAP and NOR) contain iron acting as the active center.…”

Effect of Ammonia Concentration on Shortcut Nitrification and Denitrification

“…Removal of nitrogen pollutant is an important aspect of wastewater treatment [2]. Nitrogen contained in wastewater is a pervasive and serious aquatic problem, known as eutrophication that causes excessive growth of algae and cyanobacteria [3][4]. Wastewater denitrification is gaining increasing attention.…”