Heraklion 2019: 7th International Conference on Sustainable Solid Waste Management
26-29 June 2019, Heraklion, Greece


The objective of this study was to determine the efficiency of microwave radiation technology as a drying method, and compare the energy consumption with that of electrical heating and investigate the influence of the addition of ionic species such as salt to the drying performance.


Mechanically dewatered sewage sludge samples taken from the mechanical drying outlet of city wastewater treatment plant. Salt was added to the sewage sludge with a percentage of 5% to improve the heating within the microwave energy. Moisture contents, evaporation rates, and drying performances were determined. Hot and cold regions on the dried sludge and the microwave oven, the parameters influencing the drying performance, and energy consumption were determined.


Salt addition resulted in a lower level of moisture loss, although higher temperature levels were obtained at the salt-added sludge than the sludge without salt. Salt addition to the sludge decreased the dielectric constant and increased the dielectric loss factor, thus increased the dissipation factor. It was found that electrical drying consumes more energy than the microwave oven for a certain moisture loss targeted in sewage sludge.


Several parameters can influence the efficiency of the microwave drying process of sewage sludge. An increase in the sludge temperature does not always increase the evaporation rates; changes in the dielectric properties of the sludge influence the microwave drying process. Less energy is required for microwave drying than electrical drying, which makes microwave drying a cheaper alternative when compared to electrical drying in terms of operational costs.