Date of Award

Fall 1989

Document Type

Thesis

Degree Name

Master of Science in Environmental Science - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Leonard Dauerman

Second Advisor

Richard B. Trattner

Third Advisor

John R. Schuring

Abstract

The off-site regeneration of granulated activated charcoal(GAC), spent as a result of stripping of organics from aqueous waste streams, represents a burdensome cost both because of the actual cost of regeneration and legal liability associated with shipping a hazardous waste off-site: that liability is reflected in huge potential costs associated with mishaps enroute for the self-insured or high premiums paid to the casualty insurance companies for those generators that are insured by third parties. Thus there is a need for the development of a process to effect on-site regeneration of spent GAC cost-effectively.

This thesis mainly focuses on the technical feasibility of microwave treatment to effect regeneration of GAC. This study has shown that microwave treatment of spent GAC can effect the on-site regeneration in a potentially cost-effective process. The regeneration of GAC with an adsorbed organic compound was studied. The compound was a toxic dye, namely, methylene blue. This is a polyaromatic compound containing chlorine, sulfur, and nitrogen atoms. It is a chloride salt. it is non-volatile and decomposes at 190°C. Our experiments showed that GAC with methylene blue adsorbed can be regenerated up to 100%; thus, even when a non-volatile compound is adsorbed on GAC, microwave technology can effect regeneration. The regeneration is effected utilizing microwave technology in a manner consistent with its application on-site, scaled-up. The regenerability of spent GAC was investigated for three successive cycles of adsorption and regeneration. The results showed a good regeneration capacity, even at the end of fourth adsorption and, on an average, 98.2% removal of the adsorbed organic was achieved by microwave treatment.

The process appears to proceed by the following stages: water in the GAC pores are directly heated up by the microwaves leading to volatilization; the steam, thus formed, forces the air out of the pores creating an inert atmosphere; the GAC, a strong microwave energy absorber, heats the organic to its pyrolysis temperature; the pyrolyzed organic fuses into the GAC skeleton. This mechanism explains the observed results.

More importantly, this mechanism suggests that the most intractable soil contaminants, namely, dioxins and PCBs, can be treated by microwave technology. Assuming that soil and GAC behave similarly, it is possible that the aforementioned contaminants which are polyaromatic compounds will pyrolyze. This investigation is suggested, but not undertaken, in this thesis.

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