Date of Award

Spring 1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

Dorairaja Raghu

Second Advisor

William R. Spillers

Third Advisor

Raj P. Khera

Fourth Advisor

Hsin Neng Hsieh

Fifth Advisor

N. M. Ravindra

Abstract

The study of Water Treatment Plant (WTP) residuals is of recent origin and very little information is available in literature regarding these residuals. These waste materials have high solids contents, even in the mechanically dewatered condition, making it difficult to handle. These, along with stringent environmental regulations have forced the water utilities to look for new disposal options for these residuals. For this purpose as well as for evaluating suitable options for the beneficial reuse of residuals, it is essential to characterize WTP residuals.

As the dewatered residuals are plastic, the researcher may be prompted to treat these materials as clays. But, unlike clays, these residuals lose all their plasticity and behave like granular materials upon drying and weathering. Furthermore, available literature indicates that the compaction characteristics for these materials are different depending upon whether the test is carried out from the 'wet to dry" condition or from "dry to wet" condition. Therefore, WTP residuals are different from clays, due to the presence of organics, and high concentrations of chemicals. It is postulated that the above changes in behavior of residuals are brought about by the change in structure, resulting in increased cementation and increase in grain size. This reinforces the need for characterizing these materials.

In this research, geotechnical tests were performed on six residual samples and geoenvironmental tests were carried out three on residuals to determine the causes and mechanisms responsible for the changes in behavior of residuals. Grain size analysis conducted by sieve, hydrometer analyses and particle size analyzer indicated that particle sizes increased substantially upon weathering and drying. Electron micrographs, elemental maps, X-Ray diffraction and X-Ray Fluorescence spectra were obtained. The results indicated that the particle size increase could be attributed to aggregation due to organic matter and cementation due to metal oxides such as calcium oxide. It was also observed that no leaching of metals occurred due to drying, freeze, and thaw effects.

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