Influence of single- and dual-flocculant conditioning on the geometric morphology and internal structure of activated sludge

Abstract

Polymeric ferric sulfate (PFS) and cationic polyacrylamide (CPAM) were used as flocculants in single- and dual-chemical conditioning to treat activated sludge (AS). The corresponding changes in the AS geometric and internal network structure were determined according to the size, fractal dimensions, and rheological properties of AS flocs/aggregates. Results showed that at similar capillary suction time (CST) level, the flocculant dosage was lower under dual-chemical conditioning than under single-chemical conditioning. At the optimum dosage of PFS-CPAM combination, the corresponding CST and zeta potential were 11.03s and −1.65mV, respectively. In addition, the median diameters were 0.81, 0.89 and 2.73mm, and the two-dimensional (D2) fractal dimensions were 1.98, 1.95 and 1.41 for the AS conditioned with PFS-CPAM, PFS and CPAM at their respective optimum dosage. Moreover, raw and conditioned AS exhibit thixotropic (shear thinning) properties, gel-like and weak-link structures. The mass fractal dimension values were 2.52, 2.65, 2.24, and 2.70 for the raw AS and the AS conditioned with PFS, CPAM, and PFS-CPAM, respectively. These findings indicate that inorganic flocculant conditioning facilitates the compactness of the AS flocs/aggregates. PFS hydrogel and CPAM molecules can serve as backbones of the newly formed AS flocs/aggregates.