Insight into dewatering behavior and heavy metals transformation during waste activated sludge treatment by thermally-activated sodium persulfate oxidation combined with a skeleton builder-wheat straw biochar.

This work focused on dewatering performance and heavy metals (HMs) transformation during waste activated sludge (WAS) treatment by employing thermally-activated sodium persulfate (SPS) oxidation combined with a biochar made of wheat straw (WS-BC). Results demonstrated that the combined treatment was an efficient way to improve WAS dewatering, especially when SPS and WS-BC dosages were adjusted to 120 and 150 mg/g-volatile solids (VS), respectively. After being treated at 70 °C without pH adjustment, standardized-capillary suction time (SCST) was increased to 5.03, centrifuged weight reduction (CWR) was increased to 86.8% and moisture content (MC) was decreased to 42.6%, indicating an excellent dewatering performance. The underlying mechanism identified were: (1) SPS oxidation disintegrated extracellular polymers (EPS) at high temperature, thereby releasing EPS-bound water; (2) WS-BC acted as a skeleton builder conducive to form porous structure and provide free water release channels in WAS, which was favorable to improve dewatering properties of WAS; (3) thermally-activated SPS oxidation significantly improved the solubilization and reduced the leaching toxicity of HMs in WAS; and (4) the following WS-BC treatment further reduced the leaching toxicity of HMs in WAS. Therefore, the combined technology might be a promising strategy to improve WAS dewatering and reduce HMs risks in WAS.