Facilitating component separation and cascade resource utilization of sewer sludge using alkaline plant ash

Recently, increasing attention has been paid to the field of sewer sludge. This study aims to address the separation of organic and inorganic substances in sewer sludge using plant ash. After pretreatment, the VSS reduction rate reached 30%, and the SCOD increased to 161.66-198.33 mg/L, which was 4.62-5.67 times that of the control group. The Zeta potential dropped to -19.97 mV, increasing the repulsive force on sludge particle surfaces to promote organic stripping. The stripping of proteins, polysaccharides, and humic acids into the liquid phase resulted in increases of 4.5, 2.5, and 2.9 times compared to the control group. Large molecules were degraded into small ones with disruption of α-helix of proteins. After dehydration and conditioning, the moisture content, CST and SRF were reduced to 71.30%, 19.3 s and 0.83 × 10¹² m/kg respectively. Plant ash facilitates the removal of organic matter from sewer sludge through the coupled effects of three pathways: alkaline-induced structural disruption, ion exchange-mediated EPS dissociation, and osmotic pressure-induced cell rupture and organic component dispersion. Based on dehydration conditioning, the resources of liquid and solid phases were conceived in different ways for recycling and utilization. The findings suggest that component separation by plant ash could be beneficial for the ex-situ treatment of sewer sludge, which will promote resource-saving of urban drainage systems with low cost and simple operation.