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The goal of this research was to investigate the simultaneous occurrence of nitrification and denitrification by activated sludge exposed to volatile fatty acids (VFAs) during aerobic wastewater treatment using a single-stage reactor. A mixture of VFAs was spiked directly into a continuous-stirred tank reactor (CSTR) to assess subsequent impacts on nitrite removal, nitrate formation, CO(2) fixation, total bacterial density, and dominant nitrite oxidizing bacteria (NOB) concentration (i.e., Nitrospira). The activity of the periplasmic nitrate reductase (NAP) enzyme and the presence of nap gene were also measured. A rapid decrease in the nitrate formation rate (>70% reduction) was measured for activated sludge exposed to VFAs; however, the nitrite removal rate was not reduced. The total bacterial density and Nitrospira concentration remained essentially constant; therefore, the reduction in nitrate formation rate was likely not due to heterotrophic uptake of nitrogen or to a decrease in the dominant NOB population. Additionally, VFA exposure did not impact microbial CO(2) fixation efficiency. The activity of NAP enzyme increased in the presence of VFAs suggesting that nitrate produced as a consequence of nitrite oxidation was likely further reduced to gaseous denitrification products via catalysis by NAP. Little, if any, nitrogen was discharged in the aqueous effluent of the CSTR after exposure to VFAs demonstrating that activated sludge treatment yielded compounds other than those typically produced solely by nitrification.

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Studies on the removal of toxic metals from water by genetic engineering applications are becoming more and more diverse. Especially by the expression of cysteine and thiol rich proteins such as metallothioneins in bacterial cells, a high rate of removal of metal ions from the environment is ensured. In this study, we evaluated the removal and reduction of hexavalent chromium Cr(VI)from aqueous solutions with the recombinant strains obtained by cloning the human metallothioneinsMT2A and MT3 into Escherichia coli Jm109.E. coli MT2A was the most effective strain in both Cr(VI) removal (89%in 25 mg/L Cr(VI) application) and Cr(VI) reduction (76%in 25 mg/L Cr(VI) application).Cr(VI) adsorbed per dry cell (at 25 mg/L) were 17 mg/g, 22 mg/g and 19 mg/g for Jm109, MT2A and MT3, respectively. Scanning electron microscope (SEM) images showed that the morphological structures of Cr(VI)treated cells were signi cantly damaged compared to control cells. Scanning transmission electron microscope (STEM) images showed black spots in the cytoplasm of cells treated with Cr(VI).From the shifts in the Fourier transform infrared spectroscopy analysis (FTIR) spectra of the cells treated with Cr(VI) compared to the control cells, it was determined that the groups interacting with Cr were amino, hydroxyl, methyl and sulfhydryl. When all these experimental data were evaluated together, it was concluded that all three species were effective in removing Cr(VI) from aqueous solutions and MT2A strain could be used as the most effective biotechnological tool.

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Studies on the removal of toxic metals from water by genetic engineering applications are becoming more and more diverse. Especially by the expression of cysteine and thiol rich proteins such as metallothioneins in bacterial cells, a high rate of removal of metal ions from the environment is ensured. In this study, we evaluated the removal and reduction of hexavalent chromium Cr(VI)from aqueous solutions with the recombinant strains obtained by cloning the human metallothioneinsMT2A and MT3 into Escherichia coli Jm109.E. coli MT2A was the most effective strain in both Cr(VI) removal (89%in 25 mg/L Cr(VI) application) and Cr(VI) reduction (76%in 25 mg/L Cr(VI) application).Cr(VI) adsorbed per dry cell (at 25 mg/L) were 17 mg/g, 22 mg/g and 19 mg/g for Jm109, MT2A and MT3, respectively. Scanning electron microscope (SEM) images showed that the morphological structures of Cr(VI)treated cells were significantly damaged compared to control cells. Scanning transmission electron microscope (STEM) images showed black spots in the cytoplasm of cells treated with Cr(VI).From the shifts in the Fourier transform infrared spectroscopy analysis (FTIR) spectra of the cells treated with Cr(VI) compared to the control cells, it was determined that the groups interacting with Cr were amino, hydroxyl, methyl and sulfhydryl. When all these experimental data were evaluated together, it was concluded that all three species were effective in removing Cr(VI) from aqueous solutions and MT2A strain could be used as the most effective biotechnological tool.

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