P5

MEASUREMENT OF pH DISTRIBUTION IN SOIL SAMPLES FOR REMEDIATION OF TNT USING MICROELECTRODE

The measurement system consisted of a test column, a light source, a working microelectrode and a Ag/AgCI reference electrode [tip diameter (I.D.) = lmm], and a stereomicroscope situated on a vibration isolation table with a Faraday cage. Outside of the Faraday cage, a 3-D motorized micromanipulator was used to position the tip of the microelectrode. The signals were measured with a chemical microsensor. The spatial variability of soil pH was examined based on the signal recorded with a Fisher Recordall.

The tip diameter of the pH-sensitive microelectrode was preferable to be 50 ~ 100 (m. With a smaller tip size, the tip of a microelectrode would be broken easily by the coarse particles in the soil as the microelectrode penetrated the soil sample. If the tip diameter of a microelectrode is larger than 200 (m, the electrode would damage the structure of the tested samples.

The pH of the tested soil ranged from 3.7 to 9, depending on the concentration of TNT within the soil samples and the location of the measuring point. The pH decreased and variability increased with depth. In all cases, pH spatial variances in the vertical were larger than in the horizontal. This study illustrated that pH of a soil sample can be successfully measured using a microelectrode and the soil heterogeneity and spatial dependence of pH in microscale existed.

Key words: microelectrode, pH, remediation, microscale environment