| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 90 === Wastewater sludge conditioning is an essential step towards successful sludge management practice. This thesis focuses upon two fundamental characteristics of wastewater sludge subject to polyelectrolyte flocculation, restated, the rheological properties and the mechanical dewatering efficiencies.
In the first part of this work, the rheological characteristics of the wastewater sludge were investigated by using a Haake Rheostress RS 75 rheometer. The shear creep compliance experiments and the dynamic viscosity measurements as well as the small-amplitude-oscillatory-shearing tests were conducted. The shear creep compliance experiments and the small-amplitude-oscillatory-shearing tests indicate the addition of polymer coagulants to the sludge samples will form more rigid structures. The elastic solid-like behaviors were always observed in the samples with addition of polymers. The Voigt model was successfully employed in modeling the viscoelastic retardation behavior of sludge samples in the shear creep compliance tests. Moreover, the dynamic viscosity curves of the sludge samples with/without addition of polymer could be described by the power-law model of Ostwald and de Waele at the medium shear rates, ca. 100 — 300 s-1. Consequently, addition of polymer to the sludge tends to extend the applicable ranges of the shear rates for the power-law model as well as to decrease the power-law index.
The second part of this work aimed at exploring the consolidation dewatering and centrifugal-settling processes for the flocculated wastewater sludge. The results were reported for the dynamic response of sediment cake thickness (an index for cake compaction) under various doses of polymer conditioning, compression-permeability cell configuration and mode of operation (batch and continuous) in a centrifugal settling cell. The reduction in sediment thickness of sludge by consolidation and centrifugation was found to correspond mostly well with the optimal dose determined by the capillary suction time. The relaxation/rebound of cake thickness was observed in both consolidation dewatering and centrifugal dewatering with comparable compaction/relaxation time scale ratios. The experimentally determined dynamic time scale of the cake consolidation dewatering/centrifugal sedimentation agrees reasonably well with the theory by Landman and Russel (1993).
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