The cooperative effect of mechanical dewatering and thermal drying for activated sludge deep reduction

Activated sludge is one of the most difficult sludges to dewatering, reduction of moisture content (MC) was very important for the treatment and disposal. In this paper, multiple advanced detecting and analysis methods were used to explore the cooperative mechanism and technology of mechanical dewatering (MDW) and thermal drying (TD) of activated sludge, including moisture distribution, pore structure, fractal dimension and thermal conductivity. Relationship between energy consumption and treatment efficiency during the drying process with different combination modes and parameters of dewatering were also studied. The results indicated that MDW can remove most of the free water (FW) in sludge, and the proportion of binding water (BW) after constant voltage gradient mode (G-PEDW) treatment is 36.64% less than that of MDW, which can reduce energy consumption during the subsequent TD progress. The factors including MC, moisture distribution, pore structure, fractal dimension etc., of the dewatered sludge have important influences on the energy consumption and treatment efficiency of the subsequent TD. Taking into account energy consumption and treatment efficiency comprehensively, the optimal process combination of MDW—TD is that MC of sludge is first reduced to about 60% by MDW, then to about 30% by TD, the whole energy consumption and treatment time can be reduced by 75.94%, 18.75% compared with the single TD mode. This work is helpful to understand the cooperative relationship of the dewatering-drying.