Effect of Dissolved Oxygen on Oxic/Anoxic Diauxic Lag of P.?denitrificans

Nitrogen is removed in suspended growth wastewater treatment systems by passing mixed liquor from an aerobic zone in which nitrification takes place to an anoxic zone in which denitrification takes place. Following the switch from oxygen to nitrate as terminal electron acceptor, a diauxic lag may occur. The present study tested the hypothesis that lower dissolved oxygen concentrations in the aerobic phase lead to shorter diauxic lags. Bacterial cultures exposed to low dissolved oxygen concentrations (<0.70 mg/L) during the aerobic growth phase had significantly shorter diauxic lags than cultures grown at air saturation. Furthermore, these cultures generally grew faster during the anoxic phase. These results indicate that the effect of dissolved oxygen concentration in aerobic reactors on diauxic lags and anoxic growth rates in anoxic reactors should be considered in the design and operation of nitrogen-removing, suspended growth biological treatment processes.     

Effects of Surface-Bound Fe2+ on Nitrate Reduction and Transformation of Iron Oxide(s) in Zero-Valent Iron Systems at Near-Neutral pH

Nitrate reduction in an iron/nitrate/water system with or without an organic buffer was investigated using multiple batch reactors under strict anoxic conditions. Nitrate reduction was very limited (<10%) at near-neutral pH in the absence of the organic buffer. However, nitrate reduction was greatly enhanced if the system: (1) had a low initial pH ( ～ 2–3); (2) was primed with adequate aqueous Fe2+; or (3) was in the presence of the organic buffer. In Cases (1) and (3), nitrate reduction usually was involved in three stages. The first stage was quick, and H+ ions directly participated in the corrosion of iron grains. The second stage was very slow due to the formation of amorphous oxides on the surface of iron grains, while the third stage was characterized by a rapid nitrate reduction concurrent with the disappearance of aqueous Fe2+. Results indicate that reduction of nitrate by Fe0 will form magnetite; Fe2+ (aq.) can accelerate reduction of nitrate and will be substoichiometrically consumed. Once nitrate is exhausted in the system, no more Fe2+ will be consumed. In the presence of nitrate, Fe2+ (aq) will be adsorbed onto the surface of iron grains or iron oxides; the surface-complexed Fe(II) (extracted by acetate with pH = 4.1) might be oxidized and become structural Fe(III), resulting in a steadily increasing ratio of Fe(III)/Fe(II) in the oxides formed. The transformation of nonstoichiometric amorphous iron oxides into crystalline magnetite, a nonpassive oxide, triggers the rapid nitrate removal thereafter.     

Nitrate attenuation in groundwater: a review of biogeochemical controlling processes

Biogeochemical processes controlling nitrate attenuation in aquifers are critically reviewed. An understanding of the fate of nitrate in groundwater is vital for managing risks associated with nitrate pollution, and to safeguard groundwater supplies and groundwater-dependent surface waters. Denitrification is focused upon as the dominant nitrate attenuation process in groundwater. As denitrifying bacteria are essentially ubiquitous in the subsurface, the critical limiting factors are oxygen and electron donor concentration and availability. Variability in other environmental conditions such as nitrate concentration, nutrient availability, pH, temperature, presence of toxins and microbial acclimation appears to be less important, exerting only secondary influences on denitrification rates. Other nitrate depletion mechanisms such as dissimilatory nitrate reduction to ammonium and assimilation of nitrate into microbial biomass are unlikely to be important in most subsurface settings relative to denitrification. Further research is recommended to improve current understanding on the influence of organic carbon, sulphur and iron electron donors, physical restrictions on microbial activity in dual porosity aquifers, influences of environmental condition (e.g. pH in poorly buffered environments and salinity in coastal or salinized soil settings), co-contaminant influences (particularly the contrasting inhibitory and electron donor influences of pesticides) and improved quantification of denitrification rates in the laboratory and field.     

Study of the KNO3–LiNO3 and KNO3–NaNO3–LiNO3 eutectics as phase change materials for thermal storage in a low-temperature solar power plant

For heat storage applications, the solid–liquid phase changes of the LiNO₃–KNO₃ and LiNO₃–KNO₃–NaNO₃ mixtures of eutectic compositions have been investigated by Differential Scanning Calorimetry (DSC) and with a home built calorimeter working on large samples – typically 500 g. The design of the new calorimeter matches at best the geometry and the thermal transfers in the industrial application. The kinetics of crystallization has been particularly studied. Density measurements of the salts in the liquid state allowed to calculate the volumetric storage capacity.     

The Effect of Nitrates on Thallium Based Oxycarbonate Superconductors

We have synthesised a series of compounds in both the (PbTl)Sr₄Cu₂O₇(CO₃)_1–y(NO₃)_y (0.1y0.5) and TlSr₂Ba₂Cu₂O₇(CO₃)_1–y(NO₃)_y (0.1y0.2) systems. We report the synthesis conditions of these materials, an X-ray diffraction analysis of their structure and the changes induced in superconducting behaviour produced by the introduction of nitrate groups into the starting composition.     

Effects of Selected Good’s pH Buffers on Nitrate Reduction by Iron Powder

The effects of three selected Good’s pH buffers on the performance of an Fe0/nitrate/H2O system were evaluated. The Good’s pH buffer itself did not reduce nitrate directly. Nitrate reduction by iron powder at near-neutral pH was negligible in an unbuffered system, but it was greatly enhanced with the presence of the buffer. A significant amount of aqueous Fe2+ (or Fe3+) was released after adding the Good’s pH buffer into the Fe0/H2O system with or without nitrate. In general, the pH of the buffered solution increased from the initial pH ( = ～ 4.6–5.3, depending on buffer’s pKa) to near-neutral pH. After the initial pH hiking, the pH in the system was more or less stable for a period of time ( ～ 5–10?h, usually concurrent with a fairly stable aqueous Fe2+). The pH then drifted to ～ 7.1 to 8.6, depending on the buffer’s initial concentration, the buffer’s pKa, and the consumption of Fe2+ concurrent with nitrate reduction. While a common assumption made by researchers is that Good’s pH buffers do not directly participate in reaction processes involved in contaminant remediation, this study shows that as side effects, the Good’s pH buffer may react with iron powder.     

The fate of added nitrate used in the manufacture of Emmental cheese

The aim of this study was to observe the dynamics of nitrates and nitrites during the six stages of manufacture of Emmental cheeses. Samples were taken of untreated milk, of pasteurized milk, of milk with nitrates added, of pressed cheese curd, of whey, of maturing cheese and of the final product. The samples were drawn from a commercial operation in a cheese factory in the eastern part of Slovakia. The mean NaNO₂ content in untreated and in pasteurised milk was 0.2 and 0.1 mg kg^-1, respectively and the mean NaNO₃ content was 0.9 and 0.9 mg kg^-1 respectively. Nitrates were added to the milk to prevent 'blowing' of hard cheese by micro organisms. In milk with nitrate added the mean content was 81.2 mg kg^-1 NaNO₃; the maximum value being 90.0 mg kg¹ NaNO₃. After pressing, the mean value of nitrate was found to be 20.6 mg kg^-1 NaNO₃. A considerable quantity of nitrates passed into the whey, where the mean nitrate content was 67.0 mg kg^-1 NaNO₃. The final product had a markedly decreased content of nitrates (3.3 mg kg^-1 NaNO₃) and nitrites (0.2 mg kg^-1 NaNO₂) when compared with the values in cheese during maturation (11.3 mg kg^-1 NaNO₃; 0.4 mg kg^-1 NaNO₂).     

Effect of degree of cutting of leek on physicochemical characteristics of Greek traditional sausages

Fresh-cut leek is one of the principal ingredients of Greek traditional sausages. In this study the effect of the degree of cutting of leek on the physicochemical traits of Greek traditional sausages was investigated. Leek was cut to three different degrees (coarse, medium and fine), before being mixed with meat, salt and seasonings; the mixture was placed in natural casings and stored for six days at 15–18 °C. Sausages lost about 25% of their initial weight by the end of storage. While pH decreased in all treatments, it was significantly more so (to pH 4.1) in sausages with fine-cut leek, from as early as the second day of storage. During storage all sausages showed a decrease in lightness and a change in colour from yellow to red. The internal atmosphere of the sausages with fine-cut leek showed peak CO₂ concentrations of 30% while those with coarse and medium-cut leek showed peak CO₂ concentrations of 20% by day one of storage and equibrated to 5%. Ethylene in the internal atmosphere of sausages with fine and medium-cut leek peaked by day one at 5.5 μl l⁻¹ but to only 2 μl l⁻¹ for those with coarse-cut leek. Sausage nitrate content and antioxidant capacity did not show major differences between treatments. Fine-cut leek contributed to sausage stability and quality more rapidly than medium or coarse-cut leek.