Coexistence Of Denitrification Research Articles

Nitrate Bioreduction under Cr(VI) Stress: Crossroads of Denitrification and Dissimilatory Nitrate Reduction to Ammonium.

This study explored the response of NO3--N bioreduction to Cr(VI) stress, including reduction efficiency and the pathways involved (denitrification and dissimilatory nitrate reduction to ammonium (DNRA)). Different response patterns of NO3--N conversion were proposed under Cr(VI) suppress (0, 0.5, 5, 15, 30, 50, and 80 mg/L) by evaluating Cr(VI) dose dependence, toxicity accumulation, bioelectron behavior, and microbial community structure. Cr(VI) concentrations of >30 mg/L rapidly inhibited NO3--N removal and immediately induced DNRA. However, denitrification completely dominated the NO3--N reduction pathway at Cr(VI) concentrations of <15 mg/L. Therefore, 30 and 80 mg/L Cr(VI) (R4 and R6) were selected to explore the selection of the different NO3--N removal pathways. The pathway of NO3--N reduction at 30 mg/L Cr(VI) exhibited continuous adaptation, wherein the coexistence of denitrification (51.7%) and DNRA (13.6%) was achieved by regulating the distribution of denitrifiers (37.6%) and DNRA bacteria (32.8%). Comparatively, DNRA gradually replaced denitrification at 80 mg/L Cr(VI). The intracellular Cr(III) accumulation in R6 was 6.60-fold greater than in R4, causing more severe oxidant injury and cell death. The activated NO3--N reduction pathway depended on the value of nitrite reductase activity/nitrate reductase activity, with 0.84-1.08 associated with DNRA activation and 1.48-1.57 with DNRA predominance. Although Cr(VI) increased microbial community richness and improved community structure stability, the inhibition or death of nitrogen-reducing microorganisms caused by Cr(VI) decreased NO3--N reduction efficiency.

Insight into the mechanisms of denitrification and sulfate reduction coexistence in cascade reservoirs of the Jialing River: Evidence from a multi-isotope approach

The coexistence of denitrification and bacterial sulfate reduction (BSR) processes is commonly observed in natural water systems. However, its formation mechanism remains unclear at a basin scale due to the difficulty of precise identification of these processes. To address this issue, we investigated the spatial-temporal variations in water chemistry and isotopic compositions (e.g., δ13CDIC, δ15NNO3, δ18ONO3, δ34SSO4, and δ18OSO4) in cascade reservoirs (artificial dam lakes) of the Jialing River, SW China in 2016. The results showed that the denitrification and BSR processes coexisted in the studied reservoirs, which was supported by the positive correlation between δ15NNO3 and δ18ONO3 and between δ34SSO4 and δ18OSO4, and by the decreasing concentrations of NO3− and SO42−. Moreover, covariation of Δ13CDIC, Δ15NNO3, and Δ34SSO4 indicated the dominance of heterotrophic denitrification (HD) in the reservoir waters along with the occurrence of bacterial sulfide oxidation (BSO). In addition to SO42− and NO3−, the coexistence of HD and BSR processes were also controlled by the dissolved organic carbon (DOC) in winter and dissolved oxygen (DO) contents in other seasons. Overall, the cumulative effect of cascade reservoirs caused δ15NNO3 and δ34SSO4 to display an upward trend from upstream to downstream in the Jialing River, while δ13CDIC showed an opposite downward trend, which implying that cascade reservoirs may be in favor of the coexistence of the HD and BSR processes. This study therefore concludes that the multi-isotope approach could be a useful technique to ascertain the coexistence mechanism of HD and BSR processes in reservoir water systems.

Nitrogen removal performance in pilot-scale solid-phase denitrification systems using novel biodegradable blends for treatment of waste water treatment plants effluent

In this study, three pilot-scale solid-phase denitrification (SPD) systems filled with poly-3-hydroxybutyrate-co-hyroxyvelate (PHBV), PHBV-Rice hulls (PHBV-RH) and PHBV-Sawdust (PHBV-S) were operated to treat effluent of waste water treatment pangts (WWTPs). The fast start-up and intensified nitrogen removal performance were obtained in PHBV-RH and PHBV-S systems. Besides, the optimal total nitrogen (TN) removal efficiency was obtained in PHBV-S system (91.65 ± 4.12%) with less ammonia accumulation and dissolved organic carbon (DOC) release. The significant enrichment of amx 16S rRNA and nirS genes in PHBV-RH and PHBV-S systems indicated the possible coexistence of anammox and denitrification. Miseq sequencing analysis exhibited more complex community diversity, more abundant denitrifying and fermenting bacteria in PHBV-RH and PHBV-S systems. The co-existence of denitrification and anammox might contribute to better control of nitrogen and dissolved organic carbon in PHBV-S system. The outcomes provide an economical and eco-friendly alternative to improve nitrogen removal of WWTPs effluent.

Evaluation of COD effect on anammox process and microbial communities in the anaerobic baffled reactor (ABR)

Nitrogen removal with different organic carbon effect was investigated using anaerobic baffled reactor (ABR) anammox reactor. Results indicated that organic carbon exert an important effect on nitrogen removal through anammox process. When the feeding COD concentration was lower than 99.7mgL−1, nitrogen removal could be enhanced via the coexistence of denitrification and anammox. Elevated COD could further deteriorate the anammox activity with almost complete inhibition at the COD concentration of 284.1mgL−1. The nitrogen removal contribution rate of anammox was varied from 92.7% to 6.9%. However, the anammox activity was recovered when the COD/TN was decreased from 2.33 to 1.25 with influent nitrite addition. And, the anammox process was again intensified from 27.0 to 51.2%. High-throughput Miseq sequencing analyses revealed that the predominant phylum changed from Chloroflexi to Proteobacteria with the elevated COD addition, which indicated COD concentration was the most important factor regulating the bacterial community structure.

Effect of organic matter on the performance of granular anammox process

The presence of organic matter (OM) is considered to affect anammox process adversely, while practically wastewaters containing ammonia are not free from OM. In this study, the performance of anammox granules in presence of OM was evaluated under different COD to N ratios. Low OM concentration did not affect ammonia and nitrite removal significantly but improved the total nitrogen removal via denitrifiers. High OM could suppress anammox activity, resulting in a lower ammonia removal. PCR tests revealed that there was a reduction in the number of anammox bacteria and denitrifiers quantity increased when 400mg COD/L influent was applied. A COD to N threshold ratio for anammox inhibition, defined when ammonia removal dropped to 80%, was 3.1, higher than that of flocculent sludge. This study revealed that the coexistence of denitrification and anammox was an effective strategy to treat wastewaters containing high levels of nitrogen and OM.