Accelerated biodegradation of nitrophenols in the rhizosphere of Spirodela polyrrhiza

We investigated the biodegradation of 2-nitrophenol （2-NP）, 4-nitrophenol （4-NP）, and 2,4-dinitrophenol （2,4-DNP） in the rhizosphere of Spirodela polyrrhiza plants by conducting degradation experiments with three river water samples supplemented with each nitrophenol （NP）. We then isolated NP-degrading bacteria both from the S. polyrrhiza roots and from the river water. In the river water samples, removal of the three NP was accelerated in the presence of S. polyrrhiza plants. The three NPs persisted in an autoclaved solution with sterile plants suggests that NP removal was accelerated largely by bacterial NP biodegradation rather than by adsorption and uptake by the plants. We isolated 8 strains of NP-degrading bacteria： 6 strains from the S. polyrrhiza roots and 2 strains from river water without the plants. The 2-NP- and 2,4-DNP-degrading bacteria were isolated only from the S. polyrrhiza roots. The 4-NP- degrading bacteria different from those isolated from the river water samples were also found on S. polyrrhiza roots. The 2-NP- and 4-NP-degrading strains isolated from the roots utilized the corresponding NP （0.5 mmol/L） as the sole carbon and energy source. The 2,4-DNP-degrading strains isolated from the roots showed substantial 2,4-DNP-degrading activity, but the presence of other carbon and energy sources was required for their growth. The isolated NP-degrading bacteria from the roots must have contributed to the accelerated degradation of the three NPs in the rhizosphere of S. polyrrhiza. Our results suggested that rhizoremediation with S. polyrrhiza may be effective for NP-contaminated surface water.

Effect of sinusoidal waveform and frequency on space charge characteristics of polyimide

The charge phenomena under sine and half‐wave sine voltages within the frequency range of 500 Hz are studied here.Based on the pulsed electro‐acoustic method,the traditional circuit design under high-frequency voltages is first analysed.It is found that the selection of a 186 pF protection capacitor and a 333 kΩprotection resistor can ensure that the actual voltage applied to the sample is consistent with the expected input.Based on this design,experimental results show that the polarity of the charge accumulated in the depth of the sample is determined by that of the upper electrode.Comparison results under special voltages with different amplitudes and frequencies indicate that the amount of accumulated charge under sine voltages are larger than those under positive and negative half-wave sine and DC conditions,and the samples under lower-frequency conditions show more charge accumulation.The maximum electric field strengths appear at 90 and 270 degrees of the sine voltage with a frequency of 10 Hz,and their values are 68.55 and 81.82 kV/mm,respectively.Therefore,the charge characteristics are easily affected by the voltage’s waveform and frequency parameters.The results obtained here can provide guidance for the application of insulating materials under special voltage environments.