The preparation and properties of iron-walnut shell powder microelectrolytic spherical fillers.

In order to solve the issues of caking, loss, and effluent color reversion in the application of traditional microelectrolysis, the iron-walnut shell powder microelectrolytic spherical filler was developed in this paper. The filler was prepared by walnut shell powder, iron powder, sodium silicate, and sodium humate activated by ZnCl2 as raw materials and calcined at high temperature. The effects of the mass ratios of Fe to walnut shell powder, sodium silicate content, sodium humate content, calcination temperature, and time on the removal rate of methylene blue by the spherical fillers were investigated, so as to determine the optimal preparation conditions of the spherical fillers. The pore-forming structure and the composition of the spherical fillers were also analyzed by an X-ray diffractometer (XRD), a scanning electron microscope (SEM), and an energy spectrometer (EDS). The results show that the optimal preparation conditions for the spherical fillers of 5 mm are as follows: the mass ratio of iron powder to walnut shell powder treated by 15% ZnCl2 is 1:1, sodium silicate is 15%, sodium humate is 20%, the calcination temperature is 800 °C, and the calcination time is 3 h. Compared with the conventional microelectrolysis, the removal rate of methylene blue by the spherical fillers can finally reach the same level as it did, and the phenomena of the filler hardening and clogging can be avoided.

Effect of water activity and heating rate on Staphylococcus aureus heat resistance in walnut shells.

Water activity (aw) and heating rate have shown important effects on the thermo-tolerance of pathogens in low moisture foods during thermal treatments. In this study, three strains were selected to compare the heat resistance in walnut shell powder and finally the most heat resistant S. aureus ATCC 25923 was chosen to investigate the influence of aw and heating rate using a heating block system (HBS). The results showed that S. aureus ATCC 25923 became more thermo-tolerant at lower aw. The D-values of S. aureus ATCC 25923 increased with decreasing water activity and heating rates (<1°C/min). A significant increase in heat resistance of S. aureus ATCC 25923 in walnut shell powder was observed only for the heating rates of 0.2 and 0.5°C/min but not at 1, 5 and 10°C/min. There was a rapid reduction of S. aureus ATCC 25923 at elevated temperatures from 26 to 56°C at a heating rate of 0.1°C/min. The inactivation under non-isothermal conditions was better fitted by Weibull distribution (R2=0.97 to 0.99) than first-order kinetics (R2=0.88 to 0.98). These results suggest that an appropriate increase in moisture content of in-shell walnuts and heating rate during thermal process can improve the inactivation efficiency of pathogens in low moisture foods.

Use of Walnut Shell Powder to Inhibit Expression of Fe(2+)-Oxidizing Genes of Acidithiobacillus Ferrooxidans.

Acidithiobacillus ferrooxidans is a Gram-negative bacterium that obtains energy by oxidizing Fe(2+) or reduced sulfur compounds. This bacterium contributes to the formation of acid mine drainage (AMD). This study determined whether walnut shell powder inhibits the growth of A. ferrooxidans. First, the effects of walnut shell powder on Fe(2+) oxidization and H⁺ production were evaluated. Second, the chemical constituents of walnut shell were isolated to determine the active ingredient(s). Third, the expression of Fe(2+)-oxidizing genes and rus operon genes was investigated using real-time polymerase chain reaction. Finally, growth curves were plotted, and a bioleaching experiment was performed to confirm the active ingredient(s) in walnut shells. The results indicated that both walnut shell powder and the phenolic fraction exert high inhibitory effects on Fe(2+) oxidation and H⁺ production by A. ferrooxidans cultured in standard 9K medium. The phenolic components exert their inhibitory effects by down-regulating the expression of Fe(2+)-oxidizing genes and rus operon genes, which significantly decreased the growth of A. ferrooxidans. This study revealed walnut shell powder to be a promising substance for controlling AMD.