Strategies for overcoming pH excursions for reactivated granular activated carbon: Air and carbon dioxide treatments

Water treatment facilities report that when reactivated granular activated carbon (GAC) is returned to service pH excursions may occur resulting in high pH of the treated water (e.g., pH > 9), which is a result of a calcium chemistry mechanism. Air treatments of GAC at temperatures of 673 and 723 K were found to create pH stable carbons (pH < 8.5) through the formation of acidic oxygen-containing functional groups on the carbon surface thereby neutralizing the effects of the calcium chemistry mechanism. It is proposed that carbon dioxide (CO₂) treatments at ambient temperature form pH stable carbons via physisorption, and subsequent desorption, of CO₂ forming carbonic acid upon water immersion.