Scaling behaviors of unconditioned and conditioned water treatment residuals (WTRs) based on rheological and microscopic characterization

Abstract

The evolutions of limiting viscosity (η∞), yield stress (τy), cohesion energy of WTR networks (Ec), storage modulus (G′), or critical strain (γc) for linear viscoelastic (LVE) range with the TSS content of raw water treatment residuals (WTRs) can be properly described by a power-law relationship. For conditioned WTRs, a power-law dependence of η∞, G′, τy, or critical strain γc for LVE range on the TSS content was observed. A scaling theory was developed to describe the relationships between τy and Ec of WTR networks with particle concentration Φ using fractal geometry. Then the weak-link regime was found in the raw and conditioned WTR flocs/aggregates matrix, and the corresponding mass fractal dimensions (Df) were 1.81 and 2.62 as derived from lgη∞–lgTSS relation, while were 2.69 and 2.66 from double-logarithm plots of G′ against TSS content. Microscopic image analysis revealed that the conditioned WTRs present boundary/surface and mass fractal properties, and the Df values were approximate to those determined from the rheological tests. The SAS rheological tests indicated that polymer conditioning at optimum dosage did not increase the porosity of WTR flocs/aggregates.