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Metal-reducing bacteria play an important role in the release and mobilization of arsenic from sediments into groundwater. This study aimed to investigate the influence of nitrate on arsenic bio-release. Microcosm experiments consisting of high arsenic sediments and indigenous bacterium Bacillus sp. D2201 were conducted and the effects of nitrate on the mobilization of As/Fe determined. The results show arsenic release is triggered by iron reduction, which is regulated by nitrate. Increasing the nitrate concentration from 0 to 1 and 3 mM decreased Fe(III) reduction by 62.5% and 16.9% and decreased As(V) bio-release by 41.5% and 85.5%, respectively. Moreover, the results of step-wise Wenzel sequential extractions indicate nitrate addition prevents the transformation of poorly crystalline iron oxides to well crystalline iron oxides. Overall, nitrate appears to have a dual effect, inhibiting both iron reduction and arsenic release by incubation strain D2201. This study offers new insights regarding the biogeochemistry of arsenic in groundwater systems.

Microwave impedance microscope (MIM) is a near-field microwave technology which has low emission energy and can detect samples without any damages. It has numerous advantages, which can appreciably suppress the common-mode signal as the sensing probe separates from the excitation electrode, and it is an effective device to represent electrical properties with high spatial resolution. This article reviews the major theories of MIM in detail which involve basic principles and instrument configuration. Besides, this paper summarizes the improvement of MIM properties, and its cutting-edge applications in quantitative measurements of nanoscale permittivity and conductivity, capacitance variation, and electronic inhomogeneity. The relevant implementations in recent literature and prospects of MIM based on the current requirements are discussed. Limitations and advantages of MIM are also highlighted and surveyed to raise awareness for more research into the existing near-field microwave microscopy. This review on the ongoing progress and future perspectives of MIM technology aims to provide a reference for the electronic and microwave measurement community.

This study describes a method based on the measurement of a reflection coefficient to determine the dielectric constant of a sample by near-field microwave. A mathematical relation between the reflection coefficient and the parameters of a lumped circuit was derived referring to an impedance model of the probe−sample interaction. Theoretical analysis was performed to verify the equivalent model of the interaction between the probe and the sample which is equivalent to the parallel connection of multiple capacitors in a lumped circuit. By considering an equivalent model between the probe and the sample in the near field, the [inline-formula] parameter measured by the instrument was converted into the impedance parameter between the needle tip and the sample in the near field, and the impedance parameter was used to obtain the equivalent capacitance of the sample, and the dielectric constant of the sample under testing can be deduced. Different samples under near-field probes were modelled in a high-frequency structure simulator. Using a known dielectric constant, the reflection coefficient can be calculated from the coaxial probe model, and compared with the simulation results. The feasibility of the near-field probe in determining dielectric properties is verified.