Inclusion Of Nitrite Research Articles

Including Nitrite as an Intermediate in Simultaneous Nitrification/Denitrification Membrane-Aerated Biofilm Reactor Models

Abstract Our understanding of biofilm function has been greatly increased with the aid of one-dimensional biofilm models. However, to date, there has been no evaluation of how the inclusion or exclusion of nitrite within nitrification/denitrification biofilm models may impact simulated prediction of the biofilm community composition and effluent water quality. As such, several variations of commonly assumed nitrification and denitrification models with a common set of kinetic parameters were simulated in a one-dimensional membrane-aerated biofilm model to identify the differences in simulation output with respect to simultaneous nitrification and denitrification. Our results indicated that the inclusion of nitrite as an intermediate affected the biofilm community composition, microbial activity, and effluent water quality. Even under circumstances when the predicted water quality results were similar, significant differences persisted in the microbial activity. For example, chemical oxygen demand (COD) re...

Modelling aerobic granular SBR at variable COD/N ratios including accurate description of total solids concentration

The operation of a sequencing batch reactor (SBR) with aerobic granular biomass was successfully simulated using a one-dimensional biofilm model. The biological processes considered were described based on the activated sludge model (ASM) platform with two main modifications: (i) simultaneous growth and storage of organic substrates by heterotrophic bacteria; and (ii) inclusion of nitrite as intermediate compound in the nitrification and denitrification processes. Three different operational conditions were evaluated, characterized by different chemical oxygen demand to nitrogen (COD/N) ratios in the influent of: 0, 1.25 and 5.5 kg kg −1, representing a purely autotrophic media and two heterotrophic media, respectively. An accurate description of the experimental concentrations of COD, ammonium, nitrite, nitrate, dissolved oxygen (DO) and alkalinity along the cycles was obtained. Total solids concentration inside the reactor (5.0, 2.0 and 1.0 kg VSS m −3 for (COD/N) ratio of 5.5, 1.25 and 0 kg kg −1, respectively) and biofilm density ( 23 kg m granule − 3 ) were correctly described with the model. To obtain an accurate description of both solids concentration and biofilm density different densities were defined for the particulate compounds and a porosity profile along the granule was imposed. Oxygen penetration depths obtained with the model were 0.35 × 10 −3, 0.30 × 10 −3 and 0.12 × 10 −3 m for (COD/N) ratio of 5.5, 1.25 and 0 kg kg −1, respectively. The values were in agreement with those used in the description of the porosity profiles.

Microbial sulphate reduction during anaerobic digestion: EGSB process performance and potential for nitrite suppression of SRB activity

The present study investigated mesophilic anaerobic treatment of sulphate-containing wastewater in EGSB reactors and assessed the inclusion of nitrite in the reactor influent as a method for control of biological sulphate reduction. Two EGSB reactors, R1 and R2, were operated for a period of 581 days at varying volumetric loading rates, COD/SO4(2-) ratios and influent nitrite concentrations (R2 only). COD removal efficiencies of > 93% were achieved in both reactors at influent sulphate concentrations of up to 3,000 mg l(-1). A two-fold increase in the influent sulphate concentration, giving an influent COD/SO4(2-) ratio of 2, resulted in a reduction in reactor COD removal efficiency to 84% and 89%, in R1 and R2, respectively. Despite inclusion of nitrite in the R2 influent at concentrations up to 500 mg NO2-N l(-1), sulphate reduction proceeded similarly in R2 and R1, suggesting the ineffectiveness of nitrite as a potential inhibitor of SRB

Nitrosating activity in Escherichia coli

Nitrosation activity was measured in Escherichia coli isolates and a range of nitrite reductase ( nir) mutants. Activity was only detected in intact cells and could be inhibited by a number of treatments such as sonication and osmotic shock. Aerobically-grown cells had highest nitrosation activity compared to oxygen-limited ones. Inclusion of nitrite in growth media induced high activities of nitrite reductase and for some isolates, nitrosation. Analysis of nir mutants identified two which were unable to nitrosate. This result suggested that NADH-dependent nitrite reductase was implicated either directly or indirectly in nitrosation.

Epidemiological research in stomach cancer: progress over the last ten years

In this paper the progress of epidemiological research in stomach cancer during 1980-1990 is reviewed in respect to regional variation, etiology, and formation of carcinogens. The evaluation of 4 cohort and 16 case-control studies revealed a consistently inverse relationship of stomach cancer risk with raw vegetables, fruit, and wholemeal bread consumption and with vitamin C and carotene intake. Milk, cooked vegetables and vitamins A and E were not consistently found to be related to stomach cancer risk. Positive associations of increasing consumption with stomach cancer risk were occasionally found for processed or particularly prepared meat and fish, and for nitrite. Dietary nitrate intake did not appear to be related to stomach cancer risk in these studies. This latter observation is also supported by metabolic studies in high- and low-risk areas for stomach cancer. Consistently among studies, increased risk for stomach cancer was also found for later availability of refrigeration facilities in the household, non-centralized water supply (especially well water), and high salt intake. Prospective studies agreed in an increased risk for stomach cancer for cigarette smoking, but not for alcohol drinking, whereas case-control studies showed divergent results on these factors. Recent metabolic studies in high- and low-risk areas for stomach cancer or in groups with precursor lesions, with the N-nitrosoproline test as a marker for endogenous nitrosation, revealed inconsistent results. Higher nitrite concentration and increased pH in stomach juice were found to be associated with precursor conditions for stomach cancer. It is still not clear whether intake of preformed carcinogens or endogenous formation in the stomach with or without the inclusion of nitrite is the most important source of tumor-initiating or -promoting substances. Preservation or preparation of meat and fish may play an important role in this process, and vitamin C may be an inhibiting substance.

Sensory and Quality Characteristics of Poultry Frankfurters Containing Nitrite or Sorbate

Three treatments of poultry frankfurters, made with mechanically deboned poultry (MDP), were evaluated for sensory and quality characteristics over a 6-week refrigerated-storage period. The treatments consisted of the addition of: 1) 156 ppm sodium nitrite, 2) 40 ppm sodium nitrite and .26% potassium sorbate, and 3) .26% potassium sorbate. Sensory evaluations utilized triangle tests, hedonic evaluations, and magnitude estimations of flavor and texture. Color was rated with a Gardner color difference meter. Rancidity levels were ascertained by the 2-thio-barbituric acid (TBA) test.In the triangle tests, panelists were able to differentiate between nitrite and nitrite-sorbate frankfurters, as well as between nitrite and sorbate-treated frankfurters, but not between nitrite-sorbate and sorbate frankfurters. On the hedonic scale of 1 to 9 for frankfurter flavor, all treatments were rated as 5, neither like nor dislike. In the magnitude estimation tests for flavor, no differences were found among any of the treatments. However, in color tests under normal lighting, the nitrite-treated frankfurters were judged to have twice the amount of typical frankfurter color as did the nitrite-sorbate and sorbate frankfurters. From magnitude estimation tests of texture, it was found that the inclusion of nitrite at either the 40 or 156 ppm level in frankfurters had improved texture over the ones without nitrite.Gardner color difference meter scores corresponded to the panelists evaluation for triangle tests on color. There were no differences in lightness (L) and yellowness (b) values; however, nitrite frankfurters had highest a values, the most red color. The nitrite frankfurters had low TBA values throughout the study (<. 5 mg/kg sample). The samples with sorbate or nitrite-sorbate exhibited significantly higher TBA values than the samples with nitrite only after 4 and 6 weeks storage at 4 C, possibly due to the oxidation promotion by sorbate.

INFLUENCE OF pH ON Clostridium botulinum CONTROL BY SODIUM NITRITE AND SORBIC ACID IN CHICKEN EMULSIONS

ABSTRACTThe influence of hydrogen‐ion concentration on the effectiveness of sodium nitrite and/or sorbic acid to control Clostridium botulinum growth during elevated temperature abuse (27°C) of mechanically deboned chicken meat frankfurter‐type emulsions was examined. Toxin production, spore germination (loss of heat resistance) and outgrowth, residual nitrite levels, and total microbial growth (aerobic CFU) were determined at specified times during the incubation period. The effect of sorbic acid (0.2%), alone or in combination with nitrite (40, 156 μg/g), in significantly (p &lt; 0.05) inhibiting spore germination, growth, and toxin production was pH dependent. This effect was not observed at pH values above 6.20 and it increased with decreasing pH. Inclusion of nitrite in the formulation increased the effective pH for sorbic acid inhibition of toxin production. The rapid rate of germination and outgrowth in both control and nitrite‐containing treatments was not influenced by pH in the range examined (5.93‐6.93). When sorbic acid was included in the formulation, there was a slower nitrite depletion during storage. This effect was also pH dependent and it was not observed at higher pH values (7.15). Total microbial growth was affected by decreasing pH, but not by the inclusion of nitrite and/or sorbic acid in the formulation.

Clostridium botulinum CONTROL BY SODIUM NITRITE AND SORBIC ACID IN VARIOUS MEAT AND SOY PROTEIN FORMULATIONS

ABSTRACTClostridium botulinurn inoculated frankfurter‐type mixtures formulated with different meats (mechanically deboned chicken. meat, beef, and pork) and/or soy proteins (textured, concentrate, and isolate) were incubated at 27°C. The effects of sodium nitrite and/ or sorbic acid on botulinal spore germination, outgrowth, and toxin production were determined at specified time intervals during the incubation period. Also, residual nitrite depletion and in some instances total microbial growth were measured. Sorbic acid alone (0.2%) or in combination with nitrite (80 pg/g) retarded spore germination and outgrowth, and delayed toxin production. These effects were of larger magnitude in mixtures formulated with both nitrite and sorbic acid and were greater in beef, pork, and soy proteins compared to mechanically deboned chicken meat. Nitrite (80 μg/g) alone was only slightly effective in delaying toxin production and of significance only in pork. The highest nitrite level (156 μg/g)) tested in a meat‐soy mixture was significantly inhibitory to toxin development. Botulinal germination, outgrowth, and toxin production were slower in all‐soy, control (nitrite/sorbic acid‐free) formulations than in all‐meat, control samples. Residual nitrite depletion was slower in soy formulations, especially of the textured form, compared to all‐meat treatments. Inclusion of nitrite and/or sorbic acid in the formulation did not significantly change the rate and extent of total microbial growth in meat‐soy formulations.