In situ determination of solidosity profiles during activated sludge electrodewatering

Two non-invasive techniques were evaluated for the on-line measurement of sludge solidosity profiles during both pressure and electrodewatering operations. In a first approach, a radioactive tracer adsorbed onto the sludge solids was monitored by a gamma camera. Although this technique appeared very flexible in use, the lack of resolution highly limited its usefulness for (electro)dewatering experiments. Improvement in gamma camera resolution by the development of new detectors might, however, increase the future applicability of this technique. In a second technique, nuclear magnetic resonance measurements on a specially designed electrodewatering unit were made. Hereby, reliable on-line measurements of the solidosity profiles of activated sludge during electrodewatering could be made, with a resolution of less than 1 mm. Thus, the mechanisms of electroosmotic- and pressure-driven cake dewatering could be illustrated. Given the measurement time required for measuring one sludge profile, both techniques appeared mainly suited for slowly varying processes, such as activated sludge expression, and not for fast changing processes, such as the initial phases of sludge filtration.