The effect of implemented pulsed electric field (PEF) treatment on the dehydrogenase activity of activated sludge

Abstract

The implementation of sludge disintegration in wastewater treatment processes is a possible strategy of sludge minimisation. Many sludge disintegration technologies are being explored. A new additional method of disintegration is the application of pulsed electric fields (PEF). In the PEF technique short high voltage pulses are applied to generate an electric field in the sample, which builds up an electrical potential difference between the inner and outer side of the membrane. By exceeding a critical potential a perforation of the membrane is evoked (Zimmermann et al. [1]). A benefit of PEF application on subsequent aerobic and anaerobic treatment processes is shown (Koners et al. [2], Kopplow et al [3]). In this research the attention is turned to the release of cell content and change in bio-activity of the sludge after PEF implementation. The most common tests to determine the disintegrative effect is the release of dissolved organic carbon (DOC) or the uptake of chemical oxygen demand (COD). As to determine additionally sludge activity a dehydrogenase assay (DHA) with the oxidoreduction dye resazurin was chosen. The DHA data are not dependent on the metabolism of a nutritive additive like glucose. DHA can be a useful monitoring parameter for sludge activity, though it correlates not always to found respiration activity (Strotmann et al. [4]). According to Ewald et al. [5] DHA with resazurin generally is a quick test for cell viability. The disintegrative effect of PEF implementation was tested by DOC and DHA and compared to each other. The test leads to the conclusion that for each energy input the fraction of inactivated micro-organism keeps in the same range, unaffected of the dry substance content. Consequently PEF implementation is more energy efficient when the content of dry substances is high.