Electrical and rheological properties of sewage sludge – Impact of the solid content

• Total solid content impact on sludge rheological and electrical properties was studied.
• Two regimes, liquid-like and solid-like, were evidenced.
• Sludge structure was shown to directly impact its electrical properties.
• Strong relationships were found between electrical and rheological properties.

Sludge treatment is a multistep process during which sludge is mixed, pumped, thickened and dewatered. The total solid content (TSC) increases from a few grams to more than a hundred grams per liter and as underlined by the existing literature, rheological characteristics are key criteria for sludge management. However, these characteristics remain difficult to be determined in-situ and professionals are looking for alternative techniques to evaluate them. In that context, the potential of electrical measurements has been highlighted (Dieudé-Fauvel et al., 2009, 2014). This paper investigates the additional benefits of correlating both rheological and electrical properties for sludge characterization within the range of 1–23%TSC. On a rheological point of view, results are consistent with previous literature. In parallel, electrical impedance spectroscopy allowed us to define an equivalent electrical circuit to model the sludge electrical signature. Results highlight that the circuit parameters follow two regimes according to the range of solid content, similarly to rheological properties. This work opens new insights about sludge characterization and treatment monitoring.