Energy efficient microwave drying of thick layer sewage sludge enabled by SiC reinforcement for low carbon construction material valorization

To reduce the energy consumption in the construction industry, it is crucial to develop emission reduction technologies, as well as exploiting new building materials. Sewage sludge (SS) is a potential feedstock for emerging construction materials, but its extremely high moisture content makes drying a major bottleneck in both energy demand and processing capacity. Thus, a microwave thermogravimetric system was designed and evaluated with thick layer SS drying with SiC addition (SiC: SS = 1:4, 1:2, 1:1, 2:1, 4:1, and SS), microwave power (400–800 W), and total loading (30–70 g) using transient temperature/ weight and TGA/ DTG. A dynamic microwave energy coupling effect between SiC and sludge moisture was observed during drying. Adding SiC reduced the drying time from 74.4 to 35.2 min at SiC: SS = 1:2, and produced a broad effective dehydration window with a peak weight loss rate of 0.131 wt.%/s. Microwave power showed a clear optimum: the time to reach 150 °C decreased from 47.0 min at 400 W to 28.9 min at 600 W, but it increased at higher power with higher moisture removal (20.6 wt.% at 700 W), indicating vapor pressure buildup and thick layer mass transfer limitations. Total sample loading regulated drying through the combined effects of nominal microwave input power density and mass transfer resistance. Overall, the optimal condition was SiC: SS = 1:2 with 500 W and 60 g, balancing drying time and final moisture. Based on these results, the energy-efficient SS pretreatment is a promising method for low carbon building material production.