Oxyanion Removal Using Nitrogen Tailored Activated Carbons with Electrochemical Regeneration

Open Access
Author:
Byrne, Timothy Michael
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 03, 2012
Committee Members:
  • Fred Scott Cannon, Thesis Advisor
  • Nicole Robitaille Brown, Thesis Advisor
  • Brian Dempsey, Thesis Advisor
Keywords:
  • oxyanion removal
  • sulfate
  • perchlorate
  • granular activated carbon
  • electrochemical regeneration
Abstract:
Positively charged nitrogen functional groups were introduced onto the internal and external surface of granular activated carbons (GAC) which enhanced perchlorate anion removal from drinking water sources. Nitrogen tailoring involved: a) introducing oxygen groups onto the GAC, b) adding nitrogen groups using thermal ammonia treatment, and c) quaternerizing pyridine groups to create positively charged pyridinium groups. Evolution of surface chemistry and porosity throughout the tailoring procedure was analyzed using x-ray photoelectron spectroscopy (XPS) analysis, argon adsorption porosimetry, surface charge titration, and rapid small scale column test (RSSCT). In order to test the importance of starting material on perchlorate removal, four different parent GAC of different source materials were tailored: coconut, bituminous, hard-wood, and wood. Bituminous GAC offered the best performance after tailoring procedures with up to 5500 bed volumes of removal until initial breakthrough during RSSCT for 30 ppb perchlorate spiked groundwater. The performance was 5-6 times better than the parent commercial activated carbon. Oxidation with nitric acid at different treatment temperatures resulted in surface oxygen atomic percentages of 5-25%, per XPS analysis. Ammonia treatment introduced 2-6% N. In addition, the conversion of pyridine to pyridinium was confirmed by peak fitting analysis of the XPS N1s signals and surface charge titration. Redox functionality of the alklyated groups was explored using cyclic voltammetry. Perchlorate adsorption and desorption by altering the redox state of the GAC was observed by XPS detection of perchlorate presence/absence on the GAC surface. Some capacity was also restored by bulk reduction regeneration after RSSCT and rerun in adsorption RSSCT. Composite of polypyrrole and bituminous and hardwood GAC were also produced by both chemical and electrochemical polymerization for electrically regenerable adsorption of sulfate. The composite significantly increased sulfate removal from solution in both RSSCT and istotherm vs. the pristine GAC. Removal increased with increasing pyrrole concentration during polymerization. Reduction regeneration was achieved with approximately 2/3 adsorbed sulfate released, according to quantification of adsorbed sulfate in the XPS S2p peak. The implications of redox regeneration with a relatively inexpensive media could be highly transformative to the adsorption industry.