The key for the cost-efficient application of ion exchange (IE) processes relies on the fact that resins should be effectively regenerated to ensure their operation for the maximum possible working cycles. The main objective of this research work was to examine the effect of the main parameters affecting the regeneration process of several IE resins previously used for the purification of secondary-treated olive mill wastewater (OMW-2ST), comprising regenerant concentration and type, operating temperature and flow rate. For this purpose, the impacts on the regeneration and rinse times as well as the regeneration efficiency were addressed. Results show regeneration time decreased but rinse time increased with regenerant concentration increment for all resins. As a general rule, minor flow rate (2.5 L h(-1)) provided the highest possible regeneration, whereas efficiencies above 96% were noted upon the lowest temperature examined (298 K), which have both important implications on the cost-efficiency of the regeneration and integral effluent treatment process. Finally, 0.6 L HCl 4% and 0.8 L H2SO4 2% solutions achieved complete regeneration of Dowex Marathon C and Dowex MAC 3 resins, whereas 0.7 L and 1 L NaOH 4% ensured complete regeneration of Amberlyst A26 and Amberlite IRA-67 resins, respectively. (C) 2016 Elsevier B.V. All rights reserved.