Low Nitrite Concentrations Research Articles

Effects of different substrate ratios on the enrichment of anammox bacteria at low substrate concentration

Anammox bacteria (AnAOB) can be easily enriched under high temperatures and high substrate concentrations, while the application of the mainstream anammox process in low substrate municipal sewage is still relatively uncommon. Therefore, this study investigated the enrichment of AnAOB under conditions of low ammonia nitrogen and nitrite concentration at 25 °C. Results showed that using inoculated aerobic sludge, four ASBRs (R1, R2, R3 and R4) were successfully initiated with different influent substrate (NO2−-N/NH4+-N) ratios of 1.2, 1.32, 1.4 and 1.5, respectively, with reactor start-up times were 162, 150, 120 and 134 days, respectively. The values of ΔNO2--N/ΔNH4+-N in reactors were stable at 1.17, 1.32, 1.43 and 1.53 respectively. The increase in influent substrate ratios resulted in improved TN removal rates and accelerated consumption of chemical oxygen demand (COD) during the initial start-up stage. The maximum TN removal rates achieved in the four reactors were 76.09%, 79.24%, 82.82% and 82.63%, respectively. The color of sludge gradually changes from yellowish-brown to reddish-brown. Furthermore, the surface of sludge exhibited a porous mineral structure, with crater-like cavities. The dominant anammox species in the system was identified as Candida Brocadia (3.04%). According to qPCR, the abundance of hzsB in the system is 1.65 × 1012 copies/g VSS, confirming the effective enrichment of AnAOB.

The use of automatic belt feeders in a Penaeus vannamei pilot scale super-intensive nursery and grow-out with biofloc system

This study aimed to evaluate the effect of using automatic belt feeders (BF) on water quality, growth of Penaeus vannamei, and partial budget in super-intensive pilot scale systems with biofloc technology. A nursery phase (2300 shrimp m−2) and a grow-out phase (400 shrimp m−2) were carried out with the following feeding management strategies, all with three repetitions: T1: by hand, T2: by hand + BF12h; T3: BF24h. In the nursery, a spike in total ammonia concentration was observed in the first weeks of the trial in treatment T1, possibly due to nutrients from uneaten feed. Nitrite was higher in T1 treatment than in T2 and T3. Nitrate was lower in the treatment T1 than in T2 and T3. At the grow-out trial, nitrite was higher in treatment T1 than in T2 and T3. These results indicated a slower nitrification process in T1 and more efficient in treatments where automatic feeders were used since an accumulation of nitrate was observed throughout the trials and low concentrations of nitrite were observed both in the nursery and the grow-out. In the nursery and the grow-out, the T3 treatment had a higher final weight and a lower feed conversion ratio. Furthermore, the T3 treatment had a higher yield than the T1 treatment. Treatment T3 had the highest net benefit/cost, considering the entire production cycle (nursery and grow-out). Our results strongly indicate that using automatic belt feeders allows an improvement in water quality, promotes shrimp growth, improves yield, reduces feed use, and improves the net benefits in P. vannamei super-intensive nursery and grow-out with biofloc systems.

Method Validation Study of Dipstick Urinalysis as a Screening Tool for Sodium Nitrite Toxicity.

The incidence of suicide by intentional nitrite ingestion has increased since 2017. Limited options exist for commercial laboratory analysis for nitrite/nitrate. This study investigates the use of urine dipsticks for screening at autopsy for potential toxicity with sodium nitrite and, less commonly, alkyl nitrite. Archived samples of blood, urine, vitreous fluid, and gastric contents from 4 sodium nitrite/nitrate cases, 3 alkyl nitrite cases, and 4 control cases were tested using dipsticks. A rapid, strong positive result for nitrite was in the vitreous fluid of all 4-sodium nitrite/nitrate cases, along with 2 positive urine and 1 positive gastric. The 2 alkyl nitrite inhalation toxicity cases had no positive results. One alkyl nitrite ingestion case had a positive urine. The 4 controls had negative urine: equivocal results in 2 vitreous, and 1 positive gastric. Urine dipsticks are a useful adjunct to laboratory testing for nitrite toxicity and provide a rapid, cost-effective tableside result that may guide the need for further testing. Vitreous fluid and urine appear to be the most reliable specimens, although testing of gastric liquid may be useful to corroborate oral ingestion. Dipsticks may not be a reliable adjunct for testing for alkyl nitrite toxicity via inhalation route, likely due to the much lower nitrite concentration compared to nitrite ingestion cases.

Evaluation of combined addition of nitrite and chloride on the corrosion behavior of steel bars in modified magnesium oxysulfate cement paste

Magnesium oxysulfate (MOS) cement, a new breed of eco-friendly and carbon-efficient material, boasts exceptional corrosion resistance, especially in harsh environments such as high salt and high humidity. Understanding how it affects the corrosion of steel bars is crucial for its widespread application in coastal concrete engineering. Nitrite-based inhibitors are known for their rust-preventing qualities in cementitious materials. However, more research is needed to determine if nitrite remains effective in MOS cement mixed with chloride salts. This study focuses on the combined effect of chloride and nitrite salts on the corrosion of steel bars in MOS cement. Methods like corrosion area rate, weight loss rate, natural potential, and electrochemical station are employed to study the corrosion behavior of steel in MOS cement. Microscopic techniques help unravel the influence mechanism of phase composition and microstructure on these materials. Furthermore, the study examines how chloride and nitrite contents affect the concentration of free nitrite and chloride ions in MOS cement paste. The analysis model is also established to compare simple linear adsorption, Langmuir adsorption, and Freundlich adsorption. The results indicate that chloride accelerates steel corrosion, while nitrite slows it down in the environment of mixed chloride and nitrite. In low-chloride environments, nitrite content has minimal impact on steel corrosion, but its effect becomes more pronounced in high-chloride settings. The MOS cement mixed with chloride and nitrite primarily consists of Mg(OH)2, MgCl2, MgCO3, MgO, and the 5Mg(OH)2·MgSO4·7 H2O (517 phase). The phase content of passive film on the surface of steel bar is composed primarily of Fe2O3, FeO, Fe, and FeOOH in descending order. As nitrite content increases, the absorption and concentration of free nitrite ions in the MOS cement paste gradually rise, exhibiting a linear trend. Based on the fitting calculations for three distinct adsorption relationships, notably, due to the limited adsorption capacity of MOS cement for nitrite, there's a considerable difference between the simple linear adsorption relationship and the two nonlinear adsorption models in high nitrite environments. However, in low nitrite concentrations, the difference among these three fitting adsorption relationships is little. This research can provide theoretical basis for enhancing the corrosion resistance and durability of coastal concrete engineering with high chloride exposure.

Effective chloramine management without “burn” in biofilm affected nitrifying tanks using a low dose of copper

This paper highlights the potential to effectively inhibit nitrification and restore chloramine levels using a low copper concentration in a biofilm-affected (surface-to-volume ratio 16 m−1) continuous-flow laboratory-scale chloraminated system. High nitrite and low chloramine containing tanks are always recovered with chlorine “burn” by water utilities. The “burn” is not only costly and operationally complex, but also compromises the water quality, public health, and customer relations. A laboratory system comprising five reactors connected in series was operated. Each reactor simulated conditions typically encountered in full-scale systems. Low amount of copper (0.1–0.2 mg-Cu L−1) was dosed once per day into nitrified reactors. At any given time, only one reactor was dosed with copper. Not only inhibition of nitrification, chloramine decay associated with bulk water, biofilm and sediments also improved. However, the improvement was quicker and more significant when the influent to the reactor contained a high chloramine and a low nitrite concentration. Ammonia oxidising microbes exhibited resilience when exposed to low copper and chloramine concentrations for an extended period. Chloramine decay due to planktonic microbes and chemical reactions in bulk water decreased more rapidly than decay attributed to biofilm and sediments. The concept “biostable residual chlorine” explained how copper and chloramine can inhibit nitrification. Once nitrification was inhibited, the chloramine supplied from upstream effectively continued to suppress downstream nitrification, and this effect lasted more than 50 days even at 22 °C. The findings could be used to develop short-term copper dosing strategies and prevent negative impacts of nitrification and breakpoint chlorination.

Functional polymorphisms of NOS3 and GUCY1A3 affect both nitric oxide formation and association with hypertensive disorders of pregnancy.

Impaired nitric oxide (NO) formation may be associated with endothelial dysfunction and increased cardiovascular disease risk in preeclampsia (PE). Functional single-nucleotide polymorphisms (SNPs) of nitric oxide synthase 3 (NOS3) (rs3918226) and guanylate cyclase 1, soluble, alpha 3 (GUCY1A3) (rs7692387) increase susceptibility to the adverse consequences due to inadequate generation of NO by the endothelium. However, no previous study has examined whether these SNPs affect NO formation in healthy pregnancy and in gestational hypertension (GH) and PE. Here, we compared the alleles and genotypes of NOS3 (rs3918226) and GUCY1A3 (rs7692387) SNPs in normotensive pregnant women (NP, n = 153), in GH (n = 96) and PE (n = 163), and examined whether these SNPs affect plasma nitrite concentrations (a marker of NO formation) in these groups. We further examined whether the interaction among SNP genotypes is associated with GH and PE. Genotypes were determined using TaqMan allele discrimination assays, and plasma nitrite concentrations were determined by an ozone-based chemiluminescence assay. Multifactor dimensionality reduction was used to examine the interactions among SNP genotypes. Regarding NOS3 rs3918226, the CT genotype (p = 0.046) and T allele (p = 0.020) were more frequent in NP than in GH, and GH patients carrying the CT+TT genotypes showed lower nitrite concentrations than NP carrying the CT+TT genotypes (p < 0.05). Regarding GUCY1A3 rs7692387, the GA genotype (p = 0.013) and A allele (p = 0.016) were more frequent in PE than in NP, and NP women carrying the GG genotype showed higher nitrite concentrations than GH or PE patients carrying the GG genotype (p < 0.05). However, we found no significant interactions among genotypes for these functional SNPs to be associated with GH or PE. Our novel findings suggest that NOS3 rs3918226 and GUCY1A3 rs7692387 may affect NO formation and association with hypertensive disorders of pregnancy.

Effects of the putative probiotics Bacillus licheniformis, Bacillus pumilus, and Bacillus subtilis on white leg shrimp, Litopenaeus vannamei, immune response, gut histology, water quality, and growth performance.

A commercially significant species in the aquaculture sector globally, particularly in Egypt, is Litopenaeus vannamei. The experiment's objective was to ascertain how Sanolife PRO-F impacted the growth, water quality, immunological response, and intestinal morphometry of L. vannamei. In the current investigation, which lasted 12 weeks, Sanolife PRO-F was administered to shrimp post-larvae at diet doses of 0 (control), 1 (group one), 2 (group two), and 3 (group three) g/kg diet, respectively. Each experimental group had three repetitions. In the current study, shrimp fed on probiotic-treated diets showed a considerable improvement in growth performance measures and survival rate, and the nonspecific immune response was also enhanced. Shrimp fed probiotic diets had longer and more intestinal villi overall. Shrimp fed on the G2 and G3 diets showed no appreciable differences in growth or intestinal morphology. With the G2 and G3 diet, the water had lower concentrations of nitrite and ammonia. The study's findings indicate that Sanolife PRO-F treatment at 2-3 g/kg feed promotes the growth of shrimp, immunological response, gut health and function, and water quality.

Rapid enrichment of anammox bacteria for low-strength wastewater treatment: Role of influent nitrite and nitrate ratios in sequencing batch reactors (SBRs)

Anaerobic ammonium oxidation (Anammox) bacteria (AnAOB) have a long doubling time, which represents one of the key challenges for starting up anammox-based reactors. This study investigated the effect of varied nitrite/nitrate ratios on the anammox reactor startup process using five lab-scale anammox sequencing batch reactors (SBRs) (R1-R5). Nitrate addition significantly accelerated AnAOB enrichment startup, particularly during nitrite accumulation phase. The total start-up time was shortened by 55–71 days, compared to the reactor without nitrate. In R1 (nitrite/nitrate=10:0), anammox contributed the highest nitrogen removal percentage (91%), while R2 (nitrite/nitrate=7:3), with nitrate added, exhibited the highest anammox activity (53.84 mg NH4+-N/g VSS/day) in the steady-state phase. As nitrate proportions increased (R3-R5), anammox activity gradually declined due to limited available COD required for the conversion of NO3- to NO2-. Furthermore, it was found that nitrate-added improved the sludge settleability, with lower SVI30. 16S rRNA gene revealed that Ca. Brocadia was the predominant AnAOB in R1, R2 and R3, where nitrite was the primary NOx--N species (≥50%) in the influent. While in the reactor with low concentration of nitrite (R4: nitrite/nitrate=3:7), Ca. Kuenenia was the dominant AnAOB. This study successfully established a complex and balanced ecosystem with multi-species coexistence, where AnAOB served as the primary functional group on nitrogen removal, supported by denitrification bacteria and dissimilatory nitrate reduction to ammonium (DNRA) bacteria. This study proposes a rapid start-up strategy for the anammox process, which overcomes the bottleneck of long start-up time and helps to promote the application of anammox in wastewater treatment.

Influencing factors on the activity of an enriched Nitrospira culture with granular morphology

ABSTRACT Nitrospira is a common genus of nitrite-oxidising bacteria (NOB) found in wastewater treatment plants (WWTPs). To identify the key factors influencing the composition of NOB communities, research was conducted using both sequencing batch reactor (SBR) and continuous flow reactor under different conditions. High-throughput 16S rRNA gene sequencing revealed that Nitrospira (18.79% in R1 and 25.77% in R3) was the dominant NOB under low dissolved oxygen (DO) and low nitrite ( NO 2 − -N) concentrations, while Nitrobacter (21.26% in R2) was the dominant NOB under high DO and high NO 2 − -N concentrations. Flocculent and granule sludge were cultivated with Nitrospira as the dominant genus. Compared to Nitrospira flocculent sludge, Nitrospira granule sludge had higher inhibition threshold concentrations for free ammonia (FA) and free nitrous acid (FNA). It was more likely to resist adverse environmental disturbances. Furthermore, the effects of environmental factors such as temperature, pH, and DO on the activity of Nitrospira granular sludge were also studied. The results showed that the optimum temperature and pH for Nitrospira granular sludge were 36°C and 7.0, respectively. Additionally, Nitrospira granular sludge showed a higher dissolved oxygen half-saturation constant (Ko) of 3.67 ± 0.71 mg/L due to its morphological characteristics. However, the majority of WWTPs conditions do not meet the conditions for the Nitrospira granular sludge. Thus, it can be speculated that future development of aerobic partial nitrification granular sludge may automatically eliminate the influence of Nitrospira. This study provides a theoretical basis for a deeper understanding of Nitrospira and the development of future water treatment processes.

An Integrated Model Combining Mass Transfer and Chemical Reaction for Co-Decontamination Extraction Step of PUREX Process in a Pulsed Extraction Column

ABSTRACT The accurate prediction of the extraction behaviors of various solutes in PUREX reprocessing process is crucial for the operation and implementation of the actual process. In this paper, an integrated model is developed to predict the extraction behaviors of U, Np, Pu, and HNO3 in the co-decontamination step (1A extraction step) in a pulsed extraction column. The model couples several physical and chemical processes, such as countercurrent flow, mass transfer, and chemical reaction. The mass transfer coefficients and the distribution ratios of U(VI), Pu(IV), Np(IV), Np(V), Np(VI), HNO3 and HNO2 can be obtained using this model. In particular, the redox and disproportion reactions of Np are considered in the model, and the flow direction of Np can be judged under various process conditions and the corresponding influential factors can be analyzed. The judgment is based on the yield calculated from the relative concentration profiles of Np(VI), Np(V), and Np(IV) in the two phases. For neptunium to inter 1AP step, it is necessary to select high nitric acid concentration, low nitrite concentration and especially high flow ratio. For neptunium to inter 1AW step, low nitric acid concentration, high nitrite concentration and low flow ratio are needed. Compared with the experimental data, the relative errors of the distribution ratios of various solutes are less than 30%, and the relative errors of the concentrations of U(VI) and Pu(IV) at the outlet of the organic phase are less than 10%, and our model is indicated to be reliable and applicable for co-decontamination step in the PUREX reprocessing process.

Reduced nitrite accumulation at the primary nitrite maximum in the cyclonic eddies in the western North Pacific subtropical gyre.

Nitrite, an intermediate product of the oxidation of ammonia to nitrate (nitrification), accumulates in upper oceans, forming the primary nitrite maximum (PNM). Nitrite concentrations in the PNM are relatively low in the western North Pacific subtropical gyre (wNPSG), where eddies are frequent and intense. To explain these low nitrite concentrations, we investigated nitrification in cyclonic eddies in the wNPSG. We detected relatively low half-saturation constants (i.e., high substrate affinities) for ammonia and nitrite oxidation at 150 to 200 meter water depth. Eddy-induced displacement of high-affinity nitrifiers and increased substrate supply enhanced ammonia and nitrite oxidation, depleting ambient substrate concentrations in the euphotic zone. Nitrite oxidation is more strongly enhanced by the cyclonic eddies than ammonia oxidation, reducing concentrations and accelerating the turnover of nitrite in the PNM. These findings demonstrate a spatial decoupling of the two steps of nitrification in response to mesoscale processes and provide insights into physical-ecological controls on the PNM.

Combined effects of high hydrostatic pressure and chemical pre‐treatment on physico‐chemical properties of beef, using FTIR and diffuse reflectance spectroscopy

AbstractHigh pressure processing (HPP) was combined with a previous short chemical treatment to stabilize the color of beef tissue. Beef samples were treated with a solution containing ascorbic acid, sodium chloride, and a very low concentration of sodium nitrite. The effects of pressure levels (0.1–600 MPa) and preservative solution on: (i) color properties based on diffuse reflectance spectroscopy (DRS), which determines the relative concentrations of muscle pigments, (ii) protein denaturation and changes in the secondary structures by DSC and FTIR‐ATR, were determined.At high pressures, the disappearance of DSC peaks due to protein denaturation, a decrease in the proportion of α‐helix and an increase in the percentage of disordered structures, were evidenced. DRS spectra and Kublelka‐Munk theory equations demonstrated that nitrosilmyoglobin was a more stable chromophore, decreasing discoloration of the tissue. These techniques contribute to the knowledge of the physico‐chemical properties of the tissue submitted to combined preservation processes.Practical ApplicationsThere is an increasing demand from consumers for high‐quality beef products, with significant emphasis placed on color and safety attributes. Extending the shelf life by applying high hydrostatic pressure treatment (HHP) improves food safety and will produce a positive impact on both the industry and consumers. HHP is a non‐thermal preservation technology with generally minimal effects on sensory qualities and nutritional content; however, the direct application of this technology on beef leads to the production of a product with an unacceptable pale coloration. Therefore, it must be remarked that a pre‐treatment stage by immersing the pieces in a preservative solution is essential to improve the color of beef products treated by HHP. In this regard, from a technological point of view, it is very important to know the combined effects of both stages (short chemical treatment and high‐pressure) on the quality of beef products.

Aspek Teknis Budidaya dan Profitabilitas Pembesaran Ikan Nila (Oreochromis niloticus) di Fish Factory Iwa-ke Oishi, Bogor, Jawa Barat

The grow-out phase in tilapia culture (Oreochromis niloticus) is a vital business segmentation because it is the final supply chain for fish at consumption size for the general market. This study aims to analyze the managerial aspect, and business profitability in tilapia grow-out culture at the Iwa-ke Oishi Fish Factory in Bogor, West Java. The experiment collected primary data (water quality measurement) and secondary data (interview). The tilapia grow-out culture was done by six farmers who were responsible for happas and ponds that they managed. The results showed that managerial aspects include work units, each of which has a specific role, for example, aquapartners responsible for fish culture activities and investors who provide venture capital. The two roles were linked through a profit-sharing scheme with Fish Factory Iwa-ke Oishi as the collaboration coordinator. Tilapia cultured had good growth performance, as seen from a high survival rate (70.0-82.8%), supported by good water quality with low concentrations of nitrite and nitrite during the culture period (1.5 mg/day). L and 0 mg/L, respectively). Financially, this activity was profitable and promising (payback period of 0.9 years). However, the profit margin could be improved by reducing the variable costs, such as utilizing natural biota as additional feed for tilapia to decrease the feeding cost.

Regulation of the nitrite, biogenic amine and flavor quality of Cantonese pickle by selected lactic acid bacteria

Nitrite and biogenic amines (BAs) are widely found in fermented vegetables, while there is no research about the nitrite and BAs of Cantonese pickle. Therefore, the nitrite and BAs contents of 20 commercial Cantonese pickles were analyzed. Among these Cantonese pickles, the nitrite levels of samples 9 (23.95), 11 (58.68) and 19 (46.64 mg/kg) exceeded the limit standard, and the total BAs concentration of sample 12 (1143.29 mg/kg) above the recommended safety limit. Then three lactic acid bacteria (LAB) with the higher abilities of degrading nitrite and BAs were selected from the pickle samples with low nitrite and BAs concentration, which were identified as Lactiplantibacillus plantarum S1, L. plantarum S14 and Limosilactobacillus fermentum G9, respectively. Furthermore, in order to evaluate the application potential of screened LAB in the control BAs and nitrite in Cantonese pickle, the influences of these three LAB on nitrite, BAs, organic acids, and volatile compounds of Cantonese pickles were investigated. Compared to natural fermentation group, the nitrite-peak of inoculation fermentation groups were smaller (<16 mg/kg), and their BAs contents were always at lower levels (<51 mg/kg). Moreover, these selected LAB could enrich the concentration and type of organic acids and volatile substances in Cantonese pickle. Therefore, it could be concluded that these three LAB were potential for controlling nitrite and BAs in Cantonese pickle.

Double-edged sword effects of dissimilatory nitrate reduction to ammonium (DNRA) bacteria on anammox bacteria performance in an MBR reactor

Dissimilatory nitrate reduction to ammonium (DNRA) bacteria imposing double-edged sword effects on anammox bacteria were investigated in an anammox-membrane bioreactor (MBR) experiencing an induced crash-recovery event. During the experiment, the anammox-MBR was loaded with NH4+-N:NO2−-N ratios (RatioNH4+-N: NO2−-N) of 1.20–1.60. Initially, the anammox-MBR removed over 95% of 100 mg/L NH4+-N and 132 mg/L NO2−-N (RatioNH4+-N: NO2−-N = 0.76, the well accepted stoichiometric RatioNH4+-N: NO2−-N for anammox) in the influent (Stage 0). Then, we induced a system crash-recovery event via nitrite shock loadings to better understand responses from different guilds of bacteria in anammox-MBR, loaded with 1.60 RatioNH4+-N: NO2−-N with 100 mg/L NO2−-N in the influent (Stage 1). Interestingly, the nitrogen removal by anammox bacteria was maintained for about 20 days before starting to decrease significantly. In Stage 2, we further increased influent nitrite concentration to 120 mg/L (1.33 RatioNH4+-N: NO2−-N) to simulate a high nitrite toxicity scenario for a short period of time. As expected, nitrogen removal efficiency dropped to only 16.8%. After the induced system crash, anammox-MBR performance recovered steadily to 93.2% nitrogen removal with a 1.25 RatioNH4+-N:NO2−-N and a low nitrite influent concentration of 80 mg/L NO2−-N. Metagenomics analysis revealed that a probable causality of the decreasing nitrogen removal efficiency in Stage 1 was the overgrowth of DNRA-capable bacteria. The results showed that the members within the Ignavibacteriales order (21.7%) out competed anammox bacteria (17.0%) in the anammox-MBR with elevated nitrite concentrations in the effluent. High NO2−-N loading (120 mg N/L) further caused the predominant Candidatus Kuenenia spp. were replaced by Candidatus Brocadia spp. Therefore, it was evident that DNRA bacteria posed negative effects on anammox with 1.60 RatioNH4+-N: NO2−-N. Also, when 120 mg/L NO2−-N fed to anammox-MBR (RatioNH4+-N: NO2−-N = 1.33), canonical denitrification became the primary nitrogen sink with both DNRA and anammox activities decreased. They probably fed on lysed microbial cells of anammox and DNRA. In Stage 3, a low RatioNH4+-N: NO2−-N (1.25) with 80 mg/L NO2−-N was used to rescue the system, which effectively promoted DNRA-capable bacteria growth. Although anammox bacteria's abundance was only 7.7% during this stage, they could be responsible for about 90% of the total nitrogen removal during this stage.

Fatal Nitrite Intoxication by Pickling Salt: Four Autopsy Cases

Pickling salt, also known as curing salt, is a mixture of sodium chloride and sodium nitrite, which is used for color agent and a means to facilitate food preservation. Recently, online purchase of pure sodium nitrite has been restricted, and pickling salts have been used as replacements in cases of suicidal nitrite intoxication. From November 2020 to December 2021, there were four autopsy cases of nitrite poisoning caused by pickling salt, and 10 autopsy cases of nitrite poisoning by pure sodium nitrite. Due to the low nitrite concentration in pickling salts, serum nitrite and nitrate concentration, and methemoglobin levels were relatively low in pickling salts cases. Especially, low methemoglobin levels may cause confusion in the postmortem diagnosis of fatal nitrite intoxication, so caution is required.

Regulation of Nir gene in Lactobacillus plantarum WU14 mediated by GlnR.

Nitrogen (N) is an essential element in the biosynthesis of key cellular components, such as proteins and nucleic acids, in all living organisms. Nitrite, as a form of nitrogen utilization, is the main nutrient for microbial growth. However, nitrite is a potential carcinogen that combines with secondary amines, which are breakdown products of proteins, to produce N-nitroso compounds that are strongly carcinogenic. Nitrite reductase (Nir) produced by microorganisms can reduce nitrite. Binding of GlnR to the promoter of nitrogen metabolism gene can regulate the expression of Nir operon. In this study, nitrite-resistant Lactobacillus plantarum WU14 was isolated from Pickles and its protease Nir was analyzed. GlnR-mediated regulation of L. plantarum WU14 Nir gene was investigated in this study. New GlnR and Nir genes were obtained from L. plantarum WU14. The regulation effect of GlnR on Nir gene was examined by gel block test, yeast two-hybrid system, bacterial single hybrid system and qRT-RCR. Detailed analysis showed that GlnR ound to the Nir promoter region and interacted with Nir at low nitrite concentrations, positively regulating the expression of NIR. However, the transcription levels of GlnR and Nir decreased gradually with increasing nitrite concentration. The results of this study improve our understanding of the function of the Nir operon regulatory system and serve as the ground for further study of the signal transduction pathway in lactic acid bacteria.

Model-based identification and testing of appropriate strategies to minimize N2O emissions from biofilm deammonification.

Based on a one-year pilot plant operation of a two-step biofilm nitritation-anammox pilot plant, N2O mitigation strategies were identified by applying a newly developed biofilm modeling approach. Due to adapted plant operation, the N2O emission could be diminished by 75% (8.8% → 2.3% of NH4-Noxidized_AOB). The results (measurement and simulation) confirm the huge importance of denitrification as an N2O source or N2O sink, depending on the boundary conditions. A significant reduction of N2O emissions could only be achieved with a one-step deammonification system, which is related to low nitrite and HNO2 concentrations. Increased oxygen concentrations in the bulk phase are not related to decreased emissions. N2O formation by ammonium-oxidizing bacteria (AOB) just shifts deeper into the biofilm; zones with low oxygen concentrations are not avoidable in biofilm systems. Low oxygen concentrations in the bulk phase, however, result in a reduction of the total net N2O formation due to increased activity of heterotrophic bacteria directly at the source of N2O formation (outer biofilm layer). For the model-based identification of mitigation strategies, the standard modeling approaches for biofilms were expanded by including the factor-based N2O formation and emission approach. The new model 'Biofilm/N2OISAH' was successfully validated using data from pilot-scale measurement campaigns. Altogether, the investigation confirms that the employed digital model can strongly support the development of N2O mitigation strategies without the need for specialized measurement inside the biofilm.

Cultivation of Nitrifying and Nitrifying-Denitrifying Aerobic Granular Sludge for Sidestream Treatment of Anaerobically Digested Sludge Centrate

In this study, three 1.2-L aerobic granular sludge sequencing batch reactors (AGS-SBRs) were used to cultivate nitrifying and nitrifying-denitrifying granules (w/supplemental carbon) and investigate sidestream treatment of synthetic-centrate and real-centrate samples from Ashbridges Bay Treatment Plant (ABTP) in Toronto, Ontario, Canada. Results showed that although the cultivation of distinct granules was not observed in the nitrifying reactors, sludge volume index (SVI30) values achieved while treating real and synthetic centrate were 72 ± 12 mL/g and 59 ± 11 mL/g (after day 14), respectively. Ammonia-nitrogen (NH3-N) removal in the nitrifying SBRs were 93 ± 19% and 94 ± 16% for real and synthetic centrate, respectively. Granules with a distinct round structure were successfully formed in the nitrifying-denitrifying SBR, resulting in an SVI30 of 52 ± 23 mL/g. NH3-N, chemical oxygen demand (COD) and phosphorus (P) removal in the nitrifying-denitrifying SBR were 92 ± 9%, 94 ± 5%, and 81 ± 14% (7th to 114th day), respectively with a low nitrite (NO2-N) and nitrate (NO3-N) concentration in the effluent indicating simultaneous nitrification-denitrification (SND) activity. High nutrient removal efficiencies via the nitrification and SND pathways shows that AGS technology is a viable process for treating sidestreams generated in a WWTP.

Impact of nitrite on partial nitrification in aerobic sewage treatment reactors under mainstream conditions

Stable partial nitrification is still difficult to achieve under mainstream conditions. High and low nitrite concentrations were established in two identical, completely mixed, continuous aerobic reactors in parallel to determine the effect of nitrite on partial nitrification under mainstream conditions. Influent ammonium (NH4+-N) concentrations of 50 ± 3 and 10 ± 2 mg/L were used to create high and low nitrite concentrations. Partial nitrification in the two reactors was established through an influent NH4+-N loading of 0.12 kg/(m3·d) and dissolved oxygen (DO) levels of 0.1–0.3 mg/L. In a low nitrite-type reactor, the specific activity of nitrite-oxidizing bacteria (NOB) was 0.061 ± 0.005 kg/(kg volatile suspended solids [VSS]·d), which was lower than that in the high nitrite reactor (0.085 ± 0.010 kg/(kg VSS·d)). Real-time quantitative PCR showed a significant correlation between the percentage of NOB in the bacterial communities and nitrite levels in the reactor. Compared to the NOB percentage in the high nitrite reactor (0.074 %), a lower percentage (0.049 %) occurred in the low nitrite reactor. A supplementary mathematical simulation indicated that a low nitrite concentration was critical for NOB repression at DO concentrations of 0.2–0.3 mg/L. Finally, the feasibility of the low nitrite strategy was demonstrated in a PN-ANAMMOX reactor with effluent recycling. Ammonium conversion efficiencies > 40.6 % and nitrite accumulation efficiencies > 43.1 % could be achieved at recycling ratios of 250–300 %, which created low nitrite concentrations (below 1.5 mg/L) in the aerobic zone.