Understanding the Transient Microwave Drying Performances of Industrial Sewage Sludge Towards Green Fuel and Energy

Kaihan Xie; Zhihong Liu; Man Zhang; Wenke Zhao; Yaning Zhang

doi:10.53941/gefr.2025.100013

Abstract

Drying treatment, as a critical initial processing step, enables the transformation of industrial sewage sludge into green fuels, addressing dual environmental and energy challenges. A designed microwave drying thermogravimetric experimental system was developed to investigate the effects of sludge weight (20, 25, 30, 35, and 40 g) and microwave power (400, 450, 500, 550, and 600 W) on the drying performances through analysis of transient temperature and weight. Results identified three distinct drying stages: (I) rapid preheating dominated by sensible heat absorption of free water; (II) constant-temperature stage where microwave energy primarily converted to latent heat for free water removal; (III) slower bound-water removal stage. Crucially, drying performance peaked at 30 g sludge weight. Increasing microwave power significantly enhanced efficiency, reducing total drying time by 37.4% when power rose from 400 W to 600 W. Maximum drying efficiency (81.9 wt.% moisture removal) occurred at 500 W, demonstrating a non-linear power-efficiency relationship. These findings provide essential mechanistic insights and operational parameters to optimize industrial sludge to energy processes.

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