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 carbon is described. Acidification of the sample causes carbon dioxide to evolve which is absorbed by sodium hydroxide and subsequently acidified and measured using a CO2 analyser. The method is applied to granular activated carbon, used in potable water treatment, to determine the extent of scaling caused by the precipitation of carbonate. The method was found in our laboratories 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 water treatment works in a hard water area are presented and discussed. The data show that carbonate had accumulated on the granular activated carbon, however, after a number of years in operation, loss processes were also evident. A significant difference (P<0.01) in the amount of carbonate was recorded between the upflow and downflow cells of the biflow adsorber. Large calcareous deposits over the surface of carbon particles were revealed by scanning electron microscopy. As a consequence of extended service-life of granular activated carbon, the use of acid washing to remove accumulated carbonate and improve the effectiveness of subsequent regeneration is discussed.