Drying of industrial sludge using microwave: Heating performance, mass loss, and energy analysis

Drying is an important prerequisite for sludge to be further utilized. In this study, microwave heating technology was applied for drying sludge and the influences of drying temperature (110, 130, 150, 170, 190 °C), residence time (2, 5, 8, 11, 14 min), and microwave power (500, 600, 700, 800, 900 W) on the heating performance, mass loss, and energy consumption were detailed. The results showed that the heating rate decreased rapidly at 80–90 °C and increased quickly at 130–140 °C and higher microwave power can improve the heating rate. The mass loss was in the range of 29.82–63.02 wt% and it increased with drying temperature and residence time increasing while decreased firstly and then increased with increasing microwave power. The specific energy consumption was 30.87–52.47 kJ/g and it increased with the increase of drying temperature but declined originally and then increased when residence time and microwave power rose. As compared with conventional electrical drying, microwave drying showed better performance: shorter heating time (4.92 min vs 95.5 min), higher mass loss (51.52 wt% vs 24.47 wt%), and higher energy efficiency (37.27 kJ/g vs 642.51 kJ/g), thereby being a better drying technology and a feasible method for the efficient drying of industrial sludge.