Tailoring and Regeneration of Granular Activated Carbon for Perchlorate Removal
Open Access
- Author:
- Chen, Weifang
- Graduate Program:
- Environmental Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 17, 2004
- Committee Members:
- Fred Scott Cannon, Committee Chair/Co-Chair
Bruce Ernest Logan, Committee Member
Tze Chiang Chung, Committee Member
John Michael Regan, Committee Member - Keywords:
- ammonia
tailoriong
granular activated carbon
regeneration - Abstract:
- ABSTRACT TAILORING AND REGENERATION OF GRANULAR ACTIVATED CARBON FOR PERCHLORATE REMOVAL Ph.D. Candidate: Weifang Chen Thesis Advisor: Fred S. Cannon, Associate Professor The Pennsylvania State University (University Park, PA) Department of Civil and Environmental Engineering Perchlorate contaminates waters in 15 US states that 15 million American could otherwise drink. Although, conventional granular activated carbon (GAC) has a very limited capacity for removing perchlorate, it was found that ammonia thermal tailoring could enhance its bed life. For carbon tailoring, first, a commercially available bituminous GAC was subjected to thermal treatment with ammonia at temperatures of 500-800„aC. Elemental analysis results showed that nitrogen was incorporated into the carbon matrix during the thermal treatment The ammonia treatment caused an increase in positive surface charge density, reflected in a higher pHpzc and pHIEP. This was attributed to the more basic nature of the carbon surface after its treatment in ammonia. Ammonia-tailored carbon achieved as much as a 4-fold improvement in bed life for adsorbing perchlorate as determined by rapid small-scale column tests (RSSCT) using groundwater from City of Redlands with perchlorate concentration 70-78 ppb. The RSSCTs simulated full-scale operation with high reproducibility between runs. Increased perchlorate adsorption corresponded to increased positive surface charges. Ammonia-tailored activated carbons also exhibited an increase in TOC removal. Activated carbon could also be tailored electrochemically while using ethylene diamine as the reagent. Results indicate that electrochemical treatment effectively incorporated nitrogen-containing groups onto carbon surface without damaging the carbon¡¦s surface area and pore volume. The resultant carbons had two times the adsorption capacity for perchlorate as compared with its non-tailored counterpart. An essential factor in applying activated carbon to water treatment is regeneration after exhaustion. The author also tested chemical regenerations by both calcium thiosulfate and a base/acid method in small-scale for perchlorate-exhausted conventional carbon. RSSCT results indicate that base/acid regeneration was an effective way to restore the adsorption capacity of carbon. Full-scale regeneration with base/acid did not restore as much capacity as has bench-scale RSSCTs. It was believed that short-circuiting and carbon damage by the base solution would have been this distinction. Another frequently used regeneration method is thermal regeneration. Thermal regeneration was focused on ammonia-tailored carbon. To address this, the author tested whether ammonia-tailored GAC could be regenerated after the tailored GAC had adsorbed perchlorate. Thermal regeneration tests indicated that reactivations by CO2 and NH3 at 600-800„aC for 10-20 minutes restored the perchlorate adsorption capacity of the tailored carbon. In comparison, steam regeneration at temperature >700 appears to be too harsh and reduction in carbon bed life was observed. As indicated by proximate analysis, the steam reaction removed the nitrogen that the ammonia tailoring had affixed, and this destroyed the surface chemistry characteristics that had been created during the ammonia tailoring process. It was these characteristics that are improving perchlorate adsorption.