Modification of zeolite (clinoptilolite) surface with a quaternary ammonium, hexadecyl trimethyl ammonium (HDTMA), to improve the removal efficiency of fulvic acids (FA) in a zeolite fixed bed was investigated. The experiment consisted of modifying zeolite with HDTMA followed by adsorption and desorption of FA in the column. The effects of relevant parameters, such as HDTMA loading levels, FA flow rate and eluant concentration were examined, respectively. Optimization studies show that the surfactant modified zeolite (SMZ) bed with HDTMA loading of 120% of ECEC at a flow rate of 5 BV/h had the best performance and the volume of 23 BV of 30 vol% ethanol solution with the feed flow rate of 5 BV/h was sufficient for complete regeneration of SMZ and desorption of FA. Measurements of Zeta potential of SMZ indicate that a monolayer formation is the most viable packing that enables maximum removal of FA. FA adsorption on SMZ surfaces is largely due to the hydrophobic interaction and hydrogen bonding while FA desorption depends on hydrogen bonding. Partition and mass transfer also play an important role in the adsorption and desorption of FA. (c) 2006 Elsevier B.V. All rights reserved.