Application of dielectric constant measurement in microwave sludge disintegration and wastewater puriﬁcation processes Petra Veszelovszki Kovács, Balázs Lemmer, Gábor Keszthelyi-Szabó, Cecilia Hodúr and Sándor Beszédes ABSTRACT It has been numerously veriﬁed that microwave radiation could be advantageous as a pre-treatment for enhanced disintegration of sludge. Very few data related to the dielectric parameters of wastewater of different origins are available; therefore, the objective of our work was to measure the dielectric constant of municipal and meat industrial wastewater during a continuous ﬂow operating microwave process. Determination of the dielectric constant and its change during wastewater and sludge processing make it possible to decide on the applicability of dielectric measurements for detecting the organic matter removal efﬁciency of wastewater puriﬁcation process or disintegration degree of sludge. With the measurement of dielectric constant as a function of temperature, total solids (TS) content and microwave speciﬁc process parameters regression models were developed. Our results veriﬁed that in the case of municipal wastewater sludge, the TS content has a signiﬁcant effect on the dielectric constant and disintegration degree (DD), as does the temperature. The dielectric constant has a decreasing tendency with increasing temperature for wastewater sludge of low TS content, but an adverse effect was found for samples with high TS and organic matter contents. DD of meat processing wastewater sludge was inﬂuenced signiﬁcantly by the volumetric ﬂow rate and power level, as process parameters of continuously ﬂow microwave pre-treatments. It can be concluded that the disintegration process of food industry sludge can be detected by dielectric constant measurements. From technical purposes the applicability of dielectric measurements was tested in the puriﬁcation process of municipal wastewater, as well. Determination of dielectric behaviour was a sensitive method to detect the puriﬁcation degree of municipal wastewater. Petra Veszelovszki Kovács Balázs Lemmer Gábor Keszthelyi-Szabó Cecilia Hodúr Sándor Beszédes (corresponding author) Department of Process Engineering, Faculty of Engineering, University of Szeged, Moszkvai krt. 9, H-6725 Szeged, Hungary E-mail: beszedes@mk.u-szeged.hu Key words | dielectric constant, disintegration, microwave, sludge, wastewater INTRODUCTION The degree of particulate organic matter disintegration and hydrolysis of macromolecular components is one of the key issues for the whole efﬁciency of sludge utilization processes. Polymeric and insoluble compounds, such as proteins, fats, carbohydrates, and their derivatives, are decomposed into smaller molecules by hydrolysis, such as amino acids, mono- saccharides, alcohols, or fatty acids. Due to the complex particle structure and the presence of strong cell membranes, it is difﬁcult for sludge to biodegrade directly under aerobic or anaerobic conditions. The main aim of sludge pre-treatment technologies is to disrupt the cell membranes, leading to lysis of the cells of microorganisms, and to accelerate the hydrolysis of macromolecular components. Methods of sludge disinte- gration can be based on mechanical, thermal, and chemical processes or a combination of them. Among the different sludge handling methods, microwave radiation is successfully applied in the process of the hygienization, dewatering, drying, and pre-treatment stages of anaerobic digestion (AD). Treat- ments by microwave irradiation offer advantages such as rapid and direct heating, reduction of energy loss, and better controllability compared to conventional thermal methods. Dielectric heating has a higher energetic efﬁciency than con- ventional heating due to the different way of energy transfer (Leonelli & Mason ). In conventional heating, the electric 2284 © IWA Publishing 2018 Water Science & Technology | 77.9 | 2018 doi: 10.2166/wst.2018.144 Downloaded from http://iwaponline.com/wst/article-pdf/77/9/2284/215232/wst077092284.pdf by guest on 01 February 2023