Sodium pyrophosphate-mediated deconstruction of divalent cation bridging for impairing sewer sludge adhesion: in-situ self-cleaning by gravity sewage flow

Abstract

Extracellular polymeric substances (EPS) play a crucial role in maintaining the colloidal structure of sewer sludge, which can lead to significant siltation in sewage systems. In this study, a sodium pyrophosphate (SP)-mediated divalent cation chelation strategy was proposed for disrupting divalent cation bridging and macromolecular material entanglement in EPS structure in sewer sludge to achieve adhesion degradation. At the SP dosage of 0.25 g/g TS, the total amount of extractable EPS was found to have increased 2.17 times significantly, accompanied by disruption and outward migration of gelatinous EPS. Concurrently, the functional groups transfer of macromolecules and the structural transformation of aromatic proteins were initiated. In this instance, the microbial cells were lysed, facilitating the molecular deconstruction and solubilization of aromatic proteins, humic acids and carbohydrates. The deterioration of the EPS network and the breakdown of gelatinous biopolymers resulted in significantly reduced sludge cohesion. As a consequence, the mean adhesion force decreased from 4.00 to 2.37 nN, while the total suspended solids (TSS) concentration in the effluent increased by 48.59 times, indicating substantial sludge dissolution and flotation. The loss of divalent cation bridging further increased the surface electronegativity of the sludge matrix, reducing its resistance to hydraulic erosion. In this case, sewer sludge particles could be transported downstream by gravity scouring of the effluent flow. This study demonstrates the feasibility of SP-mediated EPS disruption as an effective in-situ self-cleaning strategy for sewer system management, providing a sustainable solution for mitigating siltation and improving sewer hydraulic efficiency.

Graphical abstract

Keywords

Sewer sludge / Sodium pyrophosphate / Extracellular polymeric substances / Gelatinous structure

Highlight

	● Sodium pyrophosphate disrupted EPS and reduced sediment adhesion.
	● Sodium pyrophosphate chelated divalent cations, reducing erosion resistance.
	● Microbial cell lysis and biopolymer released in sludge were enhanced.
	● Sodium pyrophosphate treatment reduced costs and environmental disturbances.

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