Nitrite Inhibition Research Articles

Nitrite modulates aminoglycoside tolerance by inhibiting cytochrome heme-copper oxidase in bacteria

As a bacteriostatic agent, nitrite has been used in food preservation for centuries. When used in combination with antibiotics, nitrite is reported to work either cooperatively or antagonistically. However, the mechanism underlying these effects remains largely unknown. Here we show that nitrite mediates tolerance to aminoglycosides in both Gram-negative and Gram-positive bacteria, but has little interaction with other types of antibiotics. Nitrite directly and mainly inhibits cytochrome heme-copper oxidases (HCOs), and by doing so, the membrane potential is compromised, blocking uptake of aminoglycosides. In contrast, reduced respiration (oxygen consumption rate) resulting from nitrite inhibition is not critical for aminoglycoside tolerance. While our data indicate that nitrite is a promising antimicrobial agent targeting HCOs, cautions should be taken when used with other antibiotics, aminoglycosides in particular.

A novel strategy for accelerating the recovery of a Fe(II)-inhibited anammox reactor by intermittent addition of betaine: Performance, kinetics and statistical analysis

In this manuscript, Fe(II) inhibition of anammox and its recovery were investigated, and the performance, kinetics and statistical features were comprehensively studied simultaneously. Anammox was suppressed and completely inhibited by the addition of 109.29 and 378.57 mg/L Fe(II), respectively, via uncompetitive inhibition. Nitrite inhibition of anammox was best fitted by the Edwards model and Aiba model. EDTA-2Na wash (0.5, 1.0, 1.5, and 2.0 mM) had a limited effect on anammox recovery, while the addition of 2.0 mM betaine accelerated anammox recovery. Prolonged betaine addition caused an unintended reduction of anammox activity, though it self-recovered after the withdrawal of betaine. The modified Boltzmann model most accurately simulated the processes of anammox recovery using the EDTA-2Na wash, betaine regulation and self-recovery, and the modified Stover-Kincannon model was able to assess the results of anammox recovery. The one-sample t-test was successfully applied to determine the effects of these three recovery strategies on inhibited anammox, which were short-term disinhibition or long-term recovery effects. The above-mentioned results demonstrate that an intermittent addition of betaine, which is a better alternative to frequently-used but poorly-degradable EDTA, may be a useful and environmentally friendly recovery strategy for Fe(II)-inhibited anammox reactor.

Caffeine and catechin towards prevention of drug induced oxidation of hemoglobin: A spectroscopic study.

Administration of low doses of nitrates over prolonged periods in patients suffering from coronary heart disease may lead to chronic methemoglobinemia, a disease caused by oxidation of hemoglobin. Previous reports have shown that natural products like curcumin, vitamin E, vitamin C, resveratrol, etc., are capable of inhibition of nitrite induced oxidation of hemoglobin. Hence in this study we aimed to investigate the preventive role of antioxidants present in our diet, like caffeine and catechin hydrate which are commonly found in coffee and tea towards methemoglobin (met-Hb) formation. Our study revealed that when the hemolysate was pre-incubated with equimolar concentration of caffeine and its metabolite with respect to nitrite, the rate of the nitrite induced oxidation of HbA decreased from (7.33±0.54)×10-5min-1 to (7.09±1.05)×10-5min-1 and (2.98±0.06)×10-5min-1 respectively. Hence it was evident that the metabolite of caffeine, 1-methyluric acid, exhibited better efficiency at physiological concentration than its precursor. On the contrary, only 4mM catechin hydrate could enhance the rate of methemoglobin formation even in absence of nitrite and the rate of the reaction was (6.088±0.31)×10-5min-1 which is comparable with that of 400μM nitrite.

Nitrite inhibition of microalgae induced by the competition between microalgae and nitrifying bacteria

Outdoor microalgae cultivation systems treating anaerobic membrane bioreactor (AnMBR) effluents usually present ammonium oxidising bacteria (AOB) competition with microalgae for ammonium uptake, which can cause nitrite accumulation. In literature, nitrite effects over microalgae have shown controversial results. The present study evaluates the nitrite inhibition role in a microalgae-nitrifying bacteria culture.For this purpose, pilot- and lab-scale assays were carried out. During the continuous outdoor operation of the membrane photobioreactor (MPBR) plant, biomass retention time (BRT) of 2 d favoured AOB activity, which caused nitrite accumulation. This nitrite was confirmed to inhibit microalgae performance. Specifically, continuous 5-d lab-scale assays showed a reduction in the nitrogen recovery efficiency by 32, 42 and 80% when nitrite concentration in the culture accounted for 5, 10 and 20 mg N·L−1, respectively. On the contrary, short 30-min exposure to nitrite showed no significant differences in the photosynthetic activity of microalgae under nitrite concentrations of 0, 5, 10 and 20 mg N·L−1.On the other hand, when the MPBR plant was operated at 2.5-d BRT, the nitrite concentration was reduced to negligible values due to increasing activity of microalgae and nitrite oxidising bacteria (NOB). This allowed obtaining maximum MPBR performance; i.e. nitrogen recovery rate (NRR) and biomass productivity of 19.7 ± 3.3 mg N·L−1·d−1 and 139 ± 35 mg VSS·L−1·d−1, respectively; while nitrification rate (NOxR) reached the lowest value (13.5 ± 3.4 mg N·L−1·d−1).Long BRT of 4.5 d favoured NOB growth, avoiding nitrite inhibition. However, it implied a decrease in microalgae growth and the accumulation of nitrate in the MPBR effluent. Hence, it seems that optimum BRT has to be within the range 2–4.5 d in order to favour microalgae growth with respect to AOB and NOB.

Inhibition factors and kinetic model for anaerobic ammonia oxidation in a granular sludge bioreactor with Candidatus Brocadia

Varying pH and high levels of nitrite have major inhibitory effects on anaerobic ammonium oxidizing bacteria (AnAOB) and are known to interfere with the anaerobic ammonia oxidation (Anammox) process. In this study, we evaluated the effect of pH and nitrite on Anammox process performance through a predictive kinetic model. A series of batch experiments were performed in a stably operating Anammox sequencing batch reactor system with “Candidatus Brocadia” as the dominant AnAOB taxon (>95%), by varying the nitrite concentration from 40 to 378 mg/L and the pH from 6.7 and 8.5, while maintaining the NH4+-N concentration at 54.6 ± 5.6 mg/L. Dual substrate kinetics including a pH inhibition function was able to predict Anammox activity at higher NO2−-N concentrations, with a nitrite inhibition constant of 210 mg/L. A synergistic negative effect on Anammox activity was observed when combining pH and nitrite stressors. Anammox activity was completely lost at low (6.7) and high (8.5) pH conditions, but resumed after adjusting to an optimal pH (7.5 ± 0.2). We found that AnAOB bacteria are susceptible to both high nitrite concentrations and fluctuating pH levels. Based on experimental evidence and modeling, pH mediates nitrite inhibition in the Anammox process due to the accumulation of free nitrous acid. Our model can predict the outcome of different operating scenarios and help select optimal operational strategies for Anammox implementation.

Discovery of novel cage-like heterocyclic hybrids as anti-inflammatory agents through the inhibition of nitrite, PGE2 and TNF-α

Novel cage-like indolizine-acenaphthene-pyridinone heterocyclic hybrids were synthesized in good yields through [bmim]Br mediated tandem 1,3-dipolar cycloaddition-annulation sequence. The anti-inflammatory activity of these hybrids was performed using carrageenan-induced hind paw oedema, croton oil-induced ear oedema and cotton pellet-induced granuloma models. Four of these cage-like heterocyclic hybrids viz. 4b, 4d, 4e and 4j showed substantial anti-inflammatory activities against acute and chronic inflammatory models and also showed significant inhibition of PGE2, TNF-α, and nitrite levels in carrageenan-induced hind paw oedema.

Individual and combined effect of salinity and nitrite on freshwater Anammox bacteria (FAB)

Anaerobic ammonium oxidation (Anammox) based technology has potential for nitrogen removal from wastewater with high salinity, but both salt and nitrite (a substrate for Anammox) have negative effect on microbial activity. In order to achieve Anammox in saline wastewater treatment, it is essential to understand the combined effect of these two components. In this study, the individual and combined effect of salinity and nitrite on fixed film freshwater Anammox bacteria (FAB, mainly belonging to the Ca. Brocadia genus), enriched on carriers from a 1500 L pilot scale one-stage (PN/Anammox) moving bed bioreactor (MBBR), were systematically investigated by 57 pre-designed batch tests. The combined inhibition of nitrite and salinity was determined by comparing with additive and independent inhibition models. With salinity only, the specific Anammox activity (SAA) decreased with increasing salinity: 14.6 mS/cm (about 9.1 g NaCl/L) of salinity caused 50% inhibition (IC50). With nitrite only, SAA started to decrease when nitrite concentration was above 450 mg N/L (threshold) and decreased with increased nitrite (IC50 = 666 mg N/L) thereafter. Significantly, when both salinity and nitrite were elevated, both the threshold and IC50 of nitrite were reduced, with inhibition enhanced. Analysis showed that at high salinity (>14.6 mS/cm) and nitrite concentration (>666 mg N/L), inhibition was close to that predicted by simulation of additive and independent inhibition models. Within a salinity range of 4–14.6 mS/cm and nitrite concentration range of 50–666 mg N/L, the combined inhibition was more severe than prediction (p < 0.05) based on the additive and independent inhibition models and therefore it was determined to be synergistic inhibition.

Anammox reactor optimization for the treatment of ammonium rich digestate lagoon supernatant - Step feeding mitigates nitrite inhibition

A laboratory-scale anammox integrated fixed-biofilm activated sludge sequencing batch reactor (IFAS-SBR) was operated for 339 days as the post treatment of a nitritation reactor treating ammonium rich digestate lagoon supernatant. By shortening the hydraulic retention time (HRT) from 2.5 d to 1.7 d, the inorganic nitrogen (N) loading rate increased from 0.38 ± 0.00 kg m3 d−1 to 0.61 ± 0.02 kg m−3 d−1; this led to a slight enhancement in the anammox activity. While the activity of anammox bacteria was inhibited by the interim accumulation of NO2−-N (141.2 – 219.2 mg L−1) in the reactor when the HRT was further reduced to 1.2 d, changing the reactor feeding strategy mitigated the nitrite inhibition and restored anammox activity. The presence of organic carbon in lagoon supernatant facilitated the growth of heterotrophic denitrifiers in the reactor; however, this had little impact on N reduction (93.2 ± 3.8% by anammox). Additional batch experiments and sequencing batch reactor cycle tests compared anammox bacterial specific activities under different operating strategies. The dynamics of anammox bacteria and heterotrophic denitrifiers along with the operating strategy changes were documented by qPCR analyses. Our study underlines the importance of optimizing operating strategies within anammox reactor operation for treating ammonia rich digestate lagoon supernatant.

Synthesis, characterization and biological applications of selenoureas having ferrocene and substituted benzoyl functionalities

In this article we have comprehensively reported the synthesis, complete chemical characterization (FTIR, multinuclear NMR, single crystal XRD, CHNS, AAS) and biological applications of seventeen ferrocene incorporated selenoureas. Biological applications include comparative DNA binding studies (with, cyclic voltammetry), antioxidant activities (DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging), anti-inflammatory activities (nitrite inhibition), phase I enzyme inhibition activities (aromatase inhibition), phase II enzyme induction studies (quinone reductase induction) and cytotoxic studies against neuroblastoma (MYCN2 and SK-N-SH), liver cancer (Hepa 1c1c7) breast cancer (MCF-7) and human cervical carcinoma HeLa cells (ATCC® CCL-2). All the compounds showed decent structure dependent biological applications.

A sulfur and nitrogen cycle informed model to simulate nitrate treatment of reservoir souring

Nitrate treatment has been widely used in various seawater injection projects to treat biologic sulfate reduction or reservoir souring. To design a promising nitrate treatment plan, it is essential to have a comprehensive understanding of reactions that represent the microbial communities of the reservoir and mechanisms through which the souring process is inhibited. We employ a new approach of evaluating different reaction pathways to design reaction models that reflect governing microbial processes in a set of batch and flow experiments. Utilizing the designed models, we suggest dissimilatory nitrate reduction to ammonium is the main reaction pathway. Additionally, we illustrate nitrite inhibition is the major mechanism of nitrate treatment process; independent of nitrate reduction being autotrophic or heterotrophic. We introduce an inhibitory nitrate injection concentration that can inhibit souring regardless of nitrite inhibition effect and the distance between injection and production wells. Furthermore, we demonstrate that the ratio of the nitrite-nitrate reduction rate can be used to estimate nitrate treatment effectiveness. Our findings in regard to importance of nitrite inhibition mechanism and the inhibitory nitrate concentration are in accordance with the field observations.

Nitrite effect on the phosphorus uptake activity of phosphate accumulating organisms (PAOs) in pilot-scale SBR and MBR reactors

Batch tests were performed to investigate the nitrite effect on the P-uptake of biomass grown in pilot-scale SBR and MBR systems. The results showed that the nitrite has an inhibitory effect on the aerobic P-uptake of the SBR and the MBR biomasses. The degree of inhibition was observed to be 65 % and 37 % at 10 mg NO2-N/l for the SBR and the MBR respectively. Both biomasses were found capable of using nitrite as electron acceptor as effectively as nitrate. Moreover, for the SBR biomass the anoxic P-uptake rate using nitrite was found even higher (60%) than the P-uptake rate with nitrate. From a modelling point of view, the current models require appropriate extensions to describe these various effects of nitrite. Hence, an extension of the ASM2d model has been provided. Prevention of nitrite build-up in full-scale EBPRs will eliminate the nitrite inhibition problem. Alternatively one can adopt a proactive approach in which the aerobic P-uptake phase is replaced with an anoxic P-uptake phase using only nitrite as electron acceptor. Such an approach offers considerable cost savings and enhanced nitrogen and phosphorus removal. This, however, requires further research for experimental validation and testing.

Manganese Oxide Biomineralization Provides Protection against Nitrite Toxicity in a Cell-Density-Dependent Manner.

Manganese biomineralization is a widespread process among bacteria and fungi. To date, there is no conclusive experimental evidence for how and if this process impacts microbial fitness in the environment. Here, we show how a model organism for manganese oxidation is growth inhibited by nitrite, and that this inhibition is mitigated in the presence of manganese. We show that such manganese-mediated mitigation of nitrite inhibition is dependent on the culture inoculum size, and that manganese oxide (MnOX) forms granular precipitates in the culture, rather than sheaths around individual cells. We provide evidence that MnOX protection involves both its ability to catalyze nitrite oxidation into (nontoxic) nitrate under physiological conditions and its potential role in influencing processes involving reactive oxygen species (ROS). Taken together, these results demonstrate improved microbial fitness through MnOX deposition in an ecological setting, i.e., mitigation of nitrite toxicity, and point to a key role of MnOX in handling stresses arising from ROS.IMPORTANCE We present here a direct fitness benefit (i.e., growth advantage) for manganese oxide biomineralization activity in Roseobacter sp. strain AzwK-3b, a model organism used to study this process. We find that strain AzwK-3b in a laboratory culture experiment is growth inhibited by nitrite in manganese-free cultures, while the inhibition is considerably relieved by manganese supplementation and manganese oxide (MnOX) formation. We show that biogenic MnOX interacts directly with nitrite and possibly with reactive oxygen species and find that its beneficial effects are established through formation of dispersed MnOX granules in a manner dependent on the population size. These experiments raise the possibility that manganese biomineralization could confer protection against nitrite toxicity to a population of cells. They open up new avenues of interrogating this process in other species and provide possible routes to their biotechnological applications, including in metal recovery, biomaterials production, and synthetic community engineering.

Hydroxytyrosol: The Phytochemical Responsible for Bioactivity of Traditionally used Olive Pits.

The fruits of Olea europaea L. is widely consumed as food, and olive pits are utilized in folk medicine to relieve gastric disturbances. In the present study, the possible anti-inflammatory, analgesic and antioxidant activities of aqueous extracts of black (BP) and green olive (GP) pit prepared at gastric fed state pH were evaluated in vitro. Moreover, the bioactive compound, hydroxytyrosol (HT), was isolated from the extracts for the first time. According to results, GP extract (62.5 to 1000 μg/mL) showed significant anti-inflammatory activity in a dose-dependent manner and HT displayed significant nitrite inhibition at 100 μM with slight analgesic activity. Extracts and HT showed a significant antioxidant activity according to Total Antioxidant Capacity (TOAC), cupric ion reducing antioxidant capacity (CUPRAC), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays. As a conclusion, a proper formulation containing HT might be a potential remedy to relieve gastric disturbances and olive pits, can be utilized as a valuable industrial tool for the low-cost production of HT.How to cite this article: Reis R, Sipahi H, Zeybekoglu G, Celik N, Kirmizibekmez H, Kaklikkaya N, Aydin A. Hydroxytyrosol: The Factor Responsible for Bioactivity of Traditionally used Olive Pits. Euroasian J Hepatogastroenterol, 2018;8(2):126-132.

Microbial community dynamics in an ANAMMOX reactor for piggery wastewater treatment with startup, raising nitrogen load, and stable performance

Bacterial community dynamics of the ANAMMOX reactor of an integrated “UASB + SHARON + ANAMMOX” system for treating piggery wastewater were investigated using the Illumina MiSeq method with samples obtained at ~ 2-week intervals during a 314-day period. With aerobic activated sludge as seeds and low content artificial wastewater (NH4+–N 50 mg/L; NO2−–N 55 mg/L) as influent for the ANAMMOX reactor, nitrogen removal was initially observed on day 38 with a removal rate 1.3 mg N L−1 day−1, and increased to 90.4 mg N L−1 day−1 on day 55 with almost complete removal of ammonia and nitrite, indicating a successful startup of the reactor. Increasing influent load stepwise to NH4+–N 272.7 mg/L/NO2−–N 300 mg/L, nitrogen removal rate increased gradually to 470 mg N L−1 day−1 on day 228, and maintained a stable level (~ 420 mg N L−1 day−1) following introduction of SHARON effluent since day 229. Correlation between microbial community dynamics and nitrogen removal capability was significant (r = 0.489, p < 0.001). Microbial community composition was determined by influent ammonia, influent nitrite, effluent nitrate and some undefined factors. Anammox bacteria, accounting for ~ 98.7% of Planctomycetes, became detectable (0.03% relative abundance) since day 38 and increased to 0.9% on day 58, well consistent with nitrogen removal performance of the reactor. Relative abundance of anammox bacteria gradually increased to 38.4% on day 140 with stepwise increased influent load; decreased to 0.4% on day 169 because of nitrite inhibition; increased to 19.24% on day 233 when the influent load was dropped; kept at ~ 9.0% with SHARON effluent used as influent and dropped to 3.3% finally. Anammox bacteria, only Candidatus Brocadia and Ca. Kuenenia detected, were the most abundant at genus level. Ca. Brocadia related taxa were enriched firstly under low load and detectable during the entire experimental period. Three main groups represented by Ca. Brocadia related OTUs were enriched or eliminated at different loads, but Ca. Kuenenia related taxa were enriched only under high load (NO2−–N > 300 mg/L), suggesting their different niches and application for different loads. These findings improve the understanding of relationships among microbial community/functional taxa, running parameters and reactor performance, and will be useful in optimizing running parameters for rapid startup and high, stable efficiency.

Rapid start-up and performance of denitrifying granular sludge in an upflow sludge blanket (USB) reactor treating high concentration nitrite wastewater.

Denitrifying granular sludge reactor holds better nitrogen removal efficiency than other kinds of denitrifying reactors, while this reactor commonly needs seeding anaerobic granular sludge and longer period for start-up in practice, which restricted the application of denitrifying granular sludge reactor. This study presented a rapid and stable start-up method for denitrifying granular sludge. An upflow sludge blanket (USB) reactor with packings was established with flocculent activated sludge for treatment of high concentration nitrite wastewater. Results showed mature denitrifying granular sludge appeared only after 15days with highest nitrogen removal rate of 5.844kgN/(m3day), which was much higher than that of compared anoxic sequencing batch reactor (ASBR). No significant nitrite inhibition occurred in USB and denitrification performance was mainly influenced by hydraulic retention time, influent C/N ratio and internal reflux ratio. Hydraulic shear force created by upflow fluid, shearing of gaseous products and stable microorganisms adhesion on the packings might be the reasons for rapid achievement of granular sludge. Compared to inoculated sludge and ASBR, remarkable microbial communitiy variations were detected in USB. The dominance of Proteobacteria and Bacteroidetes and enrichment of species Pseudomonas_stutzeri should be responsible for the excellent denitrification performance, which further verified the feasibility of start-up method.

Performance of anammox process treating nitrogen-rich saline wastewater: Kinetics and nitrite inhibition

A sequencing batch reactor (SBR) was operated more than 200 d to treat nitrogen-rich saline wastewater by anammox process. The temperature was controlled at 35 ± 0.5 °C and the mixed liquor suspended solids (MLSS) was around 4000 mg TSS/L. Anammox reactor could gradually acclimate to 100% seawater. However, the long-term effects of 50% seawater not only affected nitrogen removal performance, resulting in a decrease of nitrogen removal rate (NRR) to 0.114 kg N/(m3·d), but also weakened sludge settling ability. The effect resulting from 50% seawater was reversible and the NRR gradually increased to 0.419 kg N/(m3·d) by adding sponge carriers. Analysis of variance (ANOVA) test shown that △NO3−-N/△NH4+-N ratio was significantly different (p < 0.05) under different seawater content. After inhibition resulting from 100% seawater, the response process of anammox could be divided into three periods. At 100% seawater, nitrogen removal performance of anammox reactor was affected when influent nitrite was higher than 150 mg N/L (NO2−-Ninf/NH4+-Ninf = 1.37 ± 0.02). Luong model was suitable to analyze inhibitory effect resulting from nitrite under saline surroundings.

Functionalized spirooxindole-indolizine hybrids: Stereoselective green synthesis and evaluation of anti-inflammatory effect involving TNF-α and nitrite inhibition

Stereoselective synthesis of a small library of novel spiroheterocyclic hybrids including indolizine, oxindole, and substituted piperidine units has been accomplished in [bmim]Br using a [3 + 2] cycloaddition strategy in good yield and were tested for their anti-inflammatory activities. The effects of compounds (4a-o) against inflammation were studied using carrageenan-induced hind paw oedema, croton oil-induced ear oedema, and cotton pellet-induced granuloma models. Among the heterocyclic hybrids, compounds 4d, 4g, and 4o showed significant anti-inflammatory activities against acute and chronic inflammatory models. These compounds also showed significant inhibition of PGE2, TNF-α, and nitrite levels in carrageenan-induced hind paw oedema. Thus it is evident from our study that these novel spiroheterocyclic hybrids 4d, 4g, and 4o displayed significant anti-inflammatory effects that involve the reduction of PGE2, TNF-α, and nitrite levels.

Structural design, synthesis and substituent effect of hydrazone-N-acylhydrazones reveal potent immunomodulatory agents

4-(Nitrophenyl)hydrazone derivatives of N-acylhydrazone were synthesized and screened for suppress lymphocyte proliferation and nitrite inhibition in macrophages. Compared to an unsubstituted N-acylhydrazone, active compounds were identified within initial series when hydroxyl, chloride and nitro substituents were employed. Structure-activity relationship was further developed by varying the position of these substituents as well as attaching structurally-related substituents. Changing substituent position revealed a more promising compound series of anti-inflammatory agents. In contrast, an N-methyl group appended to the 4-(nitrophenyl)hydrazone moiety reduced activity. Anti-inflammatory activity of compounds is achieved by modulating IL-1β secretion and prostaglandin E2 synthesis in macrophages and by inhibiting calcineurin phosphatase activity in lymphocytes. Compound SintMed65 was advanced into an acute model of peritonitis in mice, where it inhibited the neutrophil infiltration after being orally administered. In summary, we demonstrated in great details the structural requirements and the underlying mechanism for anti-inflammatory activity of a new family of hydrazone-N-acylhydrazone, which may represent a valuable medicinal chemistry direction for the anti-inflammatory drug development in general.

EFFECT OF NITRITE ON DENITRIFICATION OF WASTEWATER BY AUTOTROPHIC BACTERIA

Effect of nitrite on denitrification of synthetic wastewater using autotrophic bacteria was evaluated in both batch suspension and continuous packed column runs. Emphasis was placed to clarify the minimum concentrations of nitrite and nitrous acid that inhibit the denitrification rates. Batch suspension runs were conducted by mixing acclimatized denitrification sludge and synthetic wastewater in an Erlenmeyer flask. In continuous runs, denitrification sludge was loaded to a column packed with sulfur and limestone. The nitrite inhibition could be explained satisfactorily by substrate non-competitive inhibition model. The minimum concentration of nitrite which inhibits the nitrate and nitrite removal rate lowered with decreasing pH. In suspension runs, the minimum concentration of nitrous acid which inhibited the nitrite removal rate was 0.043 g-N/m3, while the nitrate removal rates was inhibited below 0.012 g-N/m3. Both in suspension and continuous packed column runs, nitrate removal was more sensitive against nitrite increase compared with nitrite removal. The minimum concentration of nitrite which inhibited nitrate removal rate in continuous packed column runs was lower than that in suspension runs. Keywords:Autotrophic bacteria, denitrification, inhibition, nitrite, sulfur

Effects of influent COD/N ratios on nitrous oxide emission in a sequencing biofilm batch reactor for simultaneous nitrogen and phosphorus removal

The characteristics of N2O emissions from an anaerobic/aerobic/anoxic (A/O/A) sequencing biofilm batch reactor (SBBR) were investigated under different influent COD/nitrogen (C/N) ratios (from 1–4). Results indicated that the C/N ratios affected the quantity of polyhydroxybutyrate (PHB) and residual organic substances after the anaerobic period, resulting in the largest N2O emission during aerobic period occurred at a C/N of 2. Moreover, during the anoxic PHB-driven denitrification period, the rapid decline in the dissolved N2O concentration indicated that the nitrite inhibition threshold for N2O reduction increased with the increased C/N ratios, which means the higher influent C/N ratios could lower the inhibition of nitrite on N2O reduction. Finally, more PHB and residual organic substances were provided to denitrification at a high C/N ratio, resulting in less total N2O emission was achieved at a high C/N ratio in the A/O/A SBBR.