Mechanism of thermally activated sodium persulfate–biochar skeleton treatment to improve the dewaterability of waste activated sludge

Abstract

Sludge dewatering is a necessary process in the disposal of waste activated sludge (WAS). In this study, thermally activated sodium persulfate–biochar skeleton pretreatment was performed to improve the dewaterability of sludge, and its internal mechanism was systematically elucidated. The experimental results showed that, under optimal operating conditions, the water content of WAS could be reduced from 89.7% to 61.3% of the raw sludge. Under these conditions, the capillary suction time and specific resistance to filtration were roughly 23.23% and 59.57% of those in the raw sludge, respectively. This study proposes a relationship between organic matter migration and sludge physical structure that explains the dewaterability improvement mechanism. Separate thermal treatment caused organic matter such as proteins, polysaccharides, and humic substances to dissolve, releasing their bound water. Simultaneously, changes in the surface structure (pore size reductions and BET surface area increases) deteriorated the dewaterability of WAS. The reactive oxygen species generated by the thermally activated sodium persulfate further mineralized the organic matter, simplifying the floc surface structure (pore size increases and BET surface area decreases) and finally improving the dewaterability. Under these conditions, the addition of biochar increased the pore size, and further improved sludge dewaterability.