Tailoring activated carbons for enhanced removal of natural organic matter from natural waters

Several pathways have been employed to systematically modify two granular activated carbons (GACs), F400 (coal-based) and Macro (wood-based), for examining adsorption of dissolved natural organic matter (DOM) from natural waters. A total of 24 activated carbons with different physical and chemical characteristics was produced. The impact of carbon treatment on the DOM adsorption was examined by conducting isotherm experiments at a neutral pH using the modified carbons and a DOM isolated from the influent to Myrtle Beach drinking water treatment plant in South Carolina (USA). Adsorption of the DOM by two activated carbon fibers, with relatively uniform pore size distributions, showed that only pores with widths larger than 1 nm were accessible to the DOM macromolecules. Increases in the carbon supermicropore and mesopore volume (i.e., > 1 nm) increased the DOM uptake, if the surface chemistry was favorable. The isotherms normalized on a surface area basis showed the significance of carbon surface chemistry on the DOM uptake. At neutral pH, adsorption of negatively charged DOM molecules was favored by basic and positively charged surfaces, while the DOM uptake was minimized when the surface had acidic characteristics. High temperature ammonia treatment of oxidized carbons considerably enhanced the DOM uptake, mainly due to the increase in accessible surface area and surface basicity. Iron-impregnated carbons indicated an enhanced affinity of iron-laden carbon surface toward the DOM species, if the surface was not negatively charged.