Application of a method to quantify carbonate precipitated on granular activated carbon (GAC) used in potable water treatment

A method for quantifying carbonate precipitated on granular activated carbo n is described. Acidification of the sample causes carbon dioxide to evolve which is absorbed by sodium hydroxide and subsequently acidified and measu red using a CO2 analyser. The method is applied to granular activated carbo n, used in potable water treatment, to determine the extent of scaling caus ed by the precipitation of carbonate. The method was found in our laborator ies to be highly consistent and reliable. Details of the method testing are included. The results of a 15 month field study conducted at a surface wat er treatment works in a hard water area are presented and discussed. The da ta show that carbonate had accumulated on the granular activated carbon, ho wever, alter a number of years in operation, loss processes were also evide nt. A significant difference (P < 0.01) in the amount of carbonate was reco rded between the upflow and downflow cells of th: biflow adsorber. Large ca lcareous deposits over the surface of carbon particles were revealed by sca nning electron microscopy. As a consequence of extended service-life of gra nular activated carbon, the use of acid washing to remove accumulated carbo nate and improve the effectiveness of subsequent regeneration is discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.