After pesticides (1,2-dibromo-3-chloropropane (DBCP) and 1,2,3-trichloropropane (TCP)) were found in Central Oahu's drinking water in the early 1980s, granular activated carbon (GAC) was installed to treat the groundwater. For both economic and environmental reasons, detailed studies on how to reuse the exhausted GAC began in 1997.; The ultimate goal of this on-going carbon research is to find the best scenario to reuse the spent GAC. This carbon study can be divided in five main sections including natural organic matter (NOM) characterization, investigation of factors affecting the NOM and pesticide removal, novel circulation fixed-bed (CFB) chemical regeneration pilot column study, examination of the alteration of GAC properties during the chemical regeneration processes, and development of a mathematical model for chemical regeneration of spent GAC.; An average NOM concentration of 0.092 mg as C/L was determined for Central Oahu's groundwater during this study. It was determined that the three major NOM fractions were hydrophobic acid NOM, transphilic NOM, and hydrophobic acid and neutral NOM. The dominant interaction forces between NOM and GAC were determined to be der Waals forces, electrostatic and ionic. Suitable regenerants to remove TCP and DBCP and NOM from spent GAC include 100% acetone and NaOH. NOM removal improved with increases in extraction temperature, time of extraction, and frequency of fresh NaOH solution replacement. The most promising chemical regeneration sequence is as follows: 100% acetone, warm water rinse, NaOH solution, water rinse, HCl solution, water rinse. Circulation fixed-bed (CFB) chemical regeneration pilot column studies achieved excellent removal of TCP and DBCP but only partial removal of NOM. Approximately 50% of adsorption capacity can be recovered via chemical regeneration of spent GAC.; Foreign particles including salt crystals, very fine soils and silts, and microorganisms were found on spent/regenerated GAC surfaces using Scanning Electron Microscopy. White deposits increased when regeneration temperature was increased. Zero-point charge pH investigations revealed the accumulation of acidic NOM on carbon surfaces. Fourier-Transform Infrared spectroscopy indicated that carboxylic, amide, and hydroxyl functional groups were accumulating in GAC pores. A bimodal diffusion mathematical model successfully simulated the NOM extraction phenomena.
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