The impact of ambient-temperature deep drying on the surface characteristics of sewage sludge

Proper sludge treatment is a challenge for the stable operation of municipal wastewater treatment plants, and sludge drying is a crucial step in processing water-containing sludge. The pulverization-assisted convective drying method is a deep ambient-temperature drying technique that can effectively reduce the moisture content (MC) of semi-dried sludge. This study investigates the impact of the pulverization-assisted convective drying method on the surface characteristics of sewage sludge particles. These changes were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The characterization data were further analyzed using the box fractal dimension and power spectral density (PSD) methods. The results indicate that as the blade speed increases, both the box fractal dimension (DB) values of the sludge pore structure and the PSD fractal dimension (DP) values of the sludge surface profile decrease. Additionally, the contact angle tests on the sludge surface revealed a decrease in its hydrophilicity, which facilitates the removal of moisture from the sludge. The texture properties of sludge, which reflect changes in its mechanical performance, provide valuable insights for industrial-scale treatment, as the MC decreases, adhesiveness weakens, and hardness increases.