Improved performance of gilthead sea bream, Sparus aurata, larvae after ozone disinfection of the eggs

Ozone (O₃) dissolved in seawater (ODS) was evaluated, as an egg disinfectant, on the spawn of captive gilthead sea bream, Sparus aurata, brood stock. Four contact times (CT) were tested (0.6, 1.2, 2.4 and 4.8 mg min L⁻¹) where CT was calculated by multiplying the dissolved O₃ concentration (0.3 mg L⁻¹) by different exposure periods (2, 4, 8, 16 min). There was also a disinfected seawater treatment that contained no O₃ or derived compounds (CT 0) and an untreated seawater control. All ODS treatments reduced egg surface bacterial counts to zero, which was significantly (P<0.05) lower than the CT 0 and the control groups (194 and 1320 plate⁻¹ respectively). Nevertheless, the hatching rate was high in the control and the CT treatments 0, 0.6 and 1.2 (88.7%, 87.3%, 89.5% and 83.7% respectively) while eggs exposed to a CT 2.4 and 4.8 hatched poorly (36.5% and 20.4% respectively), which was likely due, at least in part, to larvae unable to break the egg chorion successfully. Swim‐bladder inflation was significantly higher in the ODS groups (>97%) compared with the control and CT 0 treatments (ca. 70%). The results suggest that a 2‐min exposure of eggs to 0.3 mg O₃ L⁻¹ of ODS (CT 0.6) would improve current protocols in marine larviculture.     

Thermo-FTIR spectroscopic study of the siderophore ferrioxamine B: spectral analysis and stereochemical implications of iron chelation, pH, and temperature

FTIR spectra of the microbial siderophore, ferrioxamine B, and its nonchelated form (iron free; desferrioxamine B) were studied to facilitate in-depth investigation on the undisrupted structure of the siderophore and its interactions with the environment. Effects of iron chelation as well as those of various levels of pH and temperature on the stereochemical structure of the free ligand and the ferric complex were examined. The presence of a number of functional groups in these compounds and the mutual interaction between them resulted in significant shifts and overlapping of their characteristic absorption bands. Thermal and pH treatments combined with a comprehensive use of curve-fitting analysis facilitated bands resolution. Absorption bands of all functional groups were identified. The results imply that the compact and rigid structure of the ferric complex (ferrioxamine B) is sustained by intense and specific intramolecular hydrogen bonds. Dehydration was the main process observed at low temperature (25-60 degrees C). At 105 degrees C the free ligand form (desferrioxamine B) had already begun to decompose, whereas ferrioxamine B exhibited stability. The thermal destruction became acute at the 170 degrees C treatment for both molecules. The secondary amide groups and the hydroxamate groups, which comprise the binding site for the Fe atom in the complex, were found to be the most sensitive to the thermal degradation. Significant pH effects were observed only for desferrioxamine B samples at pH 9, accompanied by partial decomposition, similar to that observed at 105 degrees C. Deprotonation of desferrioxamine B was found to begin with the deprotonation of the NH(3+) group. Characteristics of the rigid conformational structure of the ferric complex and the state of the NH(3+) group, both assumed to play an important role in the recognition and uptake of the siderophore by membranal receptors, were elaborated by means of FTIR and are discussed in detail.     

Thermospectroscopic study of the adsorption mechanism of the hydroxamic siderophore ferrioxamine B by calcium montmorillonite

The behavior of iron-chelating agents in soils is highly affected by interactions with the solid phase. Still this aspect is frequently ignored. In this research the adsorption of the siderophore ferrioxamine B by Ca-montmorillonite, as a free ligand (desferrioxamine B, DFOB) and as a complex with Fe3+ (ferrioxamine B, FOB), was studied, using thermo X-ray diffraction (thermo-XRD) in the temperature range 25-360 degrees C and thermo-FTIR spectroscopy in the temperature range 25-170 degrees C. The effect of pH (4-7.5) on the adsorption was examined. Extensive use of curve-fitting analysis was required due to significant overlapping of the characteristic absorption bands of the various functional groups. Thermo-XRD analysis showed that both DFOB and FOB penetrated into the interlayer space of Ca-montmorillonite. FTIR results indicated strong interactions of DFOB within the interlayer, which involved all functional groups (NH3+, secondary amide groups, and hydroxamate groups). In contrast, the folded Fe complex of FOB retained its molecular configuration upon adsorption, and the basal spacing of the clay increased correspondingly. FOB interacted in the interlayer space of the clay, mainly through the NH of the secondary amide groups and NH3+, while the functional groups bound to the central Fe cation remained unchanged. The suspension pH had no significant effect on both DFOB and FOB adsorption at the examined range. Adsorption protected the adsorbates from thermal degradation compared to the nonadsorbed samples up to 105 degrees C. At 170 degrees C both DFOB and FOB were already partially degraded, but to a lesser extent than the nonadsorbed samples. Degradation of the molecules occurred mainly through the hydroxamic groups, which constitute the Fe-chelating center in the hydroxamic siderophore.     

Increasing the pH of Wastewater to High Levels with Different Gases—CO2 Stripping

The potential of increasing the pH of wastewater to high levels by CO₂ stripping through air, N₂, O₂ and a gas mixture (95% N₂+ 5% CO₂) has been examined in this work. Wastewater collected after the biological treatment from a large-scale plant was monitored for pH in a continuous, computer-controlled laboratory setup. The use of air as the gaseous medium for CO₂ stripping increased the pH to a maximum value of approximately 8.53. Using pure N₂ instead of air increased the pH of wastewater to a final value of 10.3 after 24 h at a flow rate of 1.5 L min^–1. An experimental system dismantling air from its CO₂ content by precipitation as CaCO₃ in a super-saturated lime solution (in a closed circulation operation), increased the pH of wastewater to a final value of 9.4 after 24 h at a flow rate of 0.7 L min^–1. Applying the same closed circulation operation to an artificial carbonate solution instead of wastewater resulted in final pH values of 9.8 after 24 h using a flow rate of 0.7 L min^–1. The results suggest that a closed circulation operation with CO₂-freed air has the potential to increase the pH of wastewater to high levels. The process may be applied for phosphorus precipitation from domestic wastewater not requiring chemicals for a pH increase.     

Comments on the mechanism of soil detachment by rainfall

The mechanisms for the detachment of soil particles by raindrops can be described by a model based on three stages. In the first stage, the soil is still dry and detachment of particles results from collisions of elastic bodies. In the second stage, the soil is fluidized and impacting raindrops cause the splash of drops of the fluidized soil. In the third stage, the fluidized soil is covered by an overland flow and drops of fluidized soil may disintegrate in the overland flow. High hydration energies of soil minerals of small particle size lead to high chemical interactions between raindrop water and soil particles and a consequent decrease of detachment of particles during the first stage. During the second and third stages, high hydration energies of minerals lead to high surface tension of fluidized soil and reduce the splashing of droplets of this fluid. The present model gives an explanation for the observed fact that the rate of particle detachment is greatest in coarse- and medium-sand-size material and is reduced at either larger or smaller particle sizes. It appears that high hydration energies are responsible for the low relative detachability of small particles.