ABSTRACT
A common practice used in water, wastewater and hazardous waste site remediation involves the use of granulated activated carbon to treat effluent waters. When the adsorption cycle is complete the contaminant saturated activated carbon is often regenerated. Regeneration commonly involves the use of high temperature steam (~800-900°C) or solvents to extract adsorbed contaminants. This process may be performed onsite or the contaminated carbon can be shipped off-site for treatment, however, both options present difficulties. Stringent emission requirements and large capital equipment investment often make on-site regeneration economically infeasible. Offsite regeneration poses the added risk of contaminant release during transport and is strongly discouraged under EPA regulations. For these reasons there is great interest in obtaining an activated carbon regeneration methodology which can be economically performed on-site while minimizing potential hazards.
The ability of ultrasound to enhance extraction of organic contaminants adsorbed on activated carbon in the presence of organic solvents has been demonstrated. The use of ultrasonic radiation to facilitate the extraction of adsorbed organic contaminants from the surface of soil and sediments into organic solvents has also been investigated and is recognized by EPA as an approved extraction technique (method #3550).. However, there is no evidence in the literature that any work has been done on using ultrasonics to induce de-adsorption in aqueous environments.
This paper presents the preliminary data from an ongoing study into the use of an ultrasonic field of varying pressure amplitude to induce physical and thermodynamic changes in contaminants adsorbed onto the surface of activated carbon. Increasing radiation intensities up to and including the cavitation point of each heterogeneous activated carbon/aqueous solution system are being investigated and physical changes in the activated carbon as well as contaminant transformation due to cavitation induced modifications examined. The aim of the research is to develop a cost-effective methodology to regenerate contaminated activated carbon, perhaps chemo-selectively.
