Document Type


Date of Award

Fall 1-31-1997

Degree Name

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


Civil and Environmental Engineering

First Advisor

Hsin Neng Hsieh

Second Advisor

Su Ling Cheng

Third Advisor

Robert Dresnack

Fourth Advisor

S. Mitra

Fifth Advisor

Dorairaja Raghu


Disposal of water treatment plant (WTP) have raised great concerns due to the stringent water quality standards and environmental regulations, and limited availability of land for ultimate disposal. The ultimate disposal of water treatment plant residuals by using monofill may be one of the most economical, and feasible options. Design and operation of such a monofill will be simple because of the uniformity of the characteristics of WTP residuals.

The objectives of this project were to determine the environmental characteristics of WTP residuals and to apply these characteristics for the design of monofills and development of the metal leaching model to predict the primary metals movement from WTP residuals in long term.

Samples of WTP residuals were collected from ten treatment facilities. Average solids content of raw residuals was 1.5 % and solids content of dewatered residuals varied from 15% to 82% in this study. It was noted that if the solids content of the residuals were below 15%, the residuals usually failed the paint filter tests. The pH of WTP residuals mainly depends on the coagulant added. The pH of alum and ferric residuals were generally neutral and the pH of lime residuals ranged from 9 to 12. The pH value and buffer capacity of lime residual were high. This is beneficial since it prevents metal from leaching. A high cation exchange capacity (CEC) of WTP residuals (20 to 35 meq/100g) generally connotes potentially a high capacity to maintain contaminants in the residuals.

There is a direct relationship between what were inside the residual and what leached out. Metal contents, pH, and CEC in dewatered residuals are found to be related to types of water sources, impurities of water sources, and chemicals added during water purification and dewatering processes.

The toxicity characteristics leaching procedure (TCLP) analysis for WTP dewatered residuals from ten water treatment facilities were conducted. Analytical results show that the concentrations of the TCLP regulated compounds in all samples were below the regulation limits. This indicates that the WTP residual tested were non hazardous.

There was no significant change in solids content, volatile solids content, and primary metals contents among the fresh, six-month, and one year-old samples taken from minimonofill. The results of field study indicated that most metals and organics remained in WTP residuals and no significant biodegradation noticed.

A mathematical predictive leaching model for major metal ions in WTP residuals are developed using diffusion theory, metals solubility, and adsorption mechanisms. This leach model can be used to predict long term primary metals leaching and to quantify immobilization of these elements for WTP residuals. WTP monofill disposal is better than MSW landfill disposal based on the leachbility studies and leaching model prediction.



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