A potential online quantifier of sludge dewaterability developed from the similitude of water and electricity: Understanding the water release resistances as the medium

Chemical conditioning is a common but chemicals consuming procedure for improving sludge dewatering performance. However, real-time monitoring of dewaterability for accurate regulation of conditioner dosage is still tricky. One of the pending questions causing this challenge is that the key mechanisms affecting water release are not fully revealed. This study traced the entire process of water release in sludge flocs to investigate and clarify the possible release resistances, including the viscous resistance derived from binding effect of contact interface, and the interfacial resistance originating from morphology of pore wall, as well as the resistance arising from structure of flocs. Key resistances in an individual nanopore were determined using the state-of-art principles in confined water flow. Then the investigation was expanded to the multi-porous flocs scale. Based on the water release behavior and inspired by the similitude of water and electricity, an online quantifier derived from electrical impedance spectroscopy (EIS) analysis was developed to achieve real-time determination of dewaterability in a probe-like type. Our results showed that both viscous resistance of pores and structural resistance of flocs affected the water release, the contribution of flocs structural resistance cannot be neglected. Moreover, strong linear correlations (r & GE; 0.943, p < 0.01) were obtained between the online quantifier, named normalized spectral dimension, and the sludge dewaterability in two typical sludge conditioning processes. The optimal dosages were successfully revealed by normalized spectral dimension in an established semi-automatic conditioning and online dewaterability monitoring system. These observations may promote the development of smart sludge treatment technologies.

Automated summary

This study investigated the key mechanisms affecting water release in sludge flocs and developed an online quantifier, based on electrical impedance spectroscopy analysis, to determine dewaterability in real-time. The results showed that both floc structural resistance and viscous resistance of pores affected water release. The developed online quantifier, called normalized spectral dimension, exhibited strong linear correlations with sludge dewaterability in two typical sludge conditioning processes. The findings may contribute to the development of smart sludge treatment technologies.