Esben Auken

In Denmark and several other countries drinking water originates from groundwater treated in open sand filters. Due to iron oxidation, the upper 30 cm of the filter clogs over time, so for optimal performance, the open sand filters must be backwashed periodically. However, often the waterworks has insufficient knowledge about the clogging process and the backwash is not performed efficiently. In this project, we try to optimize the backwash process by monitoring the clogging process, by time-domain induced polarization (TDIP) measurements. The setup consisted of 14 electrodes installed at various depth along a 2D profile within the filter, and full-waveform IP data, sampled at 3750 Hz, was recorded on a daily basis. The environment inside the water-filter proved to be very noisy, so special care in the signal processing was necessary. In particular, harmonic de-noising was essential to retrieve reliable IP data. We present the preliminary results from this study.