Commonly used pulp bleaching processes mostly employ chlorine-containing agents combined with oxygen bleaching. Totally chlorine-free bleaching processes deliver high pulp qualities, but the processes are more expensive. We have developed an environmentally friendly electrochemical mediator-based (EMB) delignification process which is designed to be cheap in chemical costs because the mediator is recycled in the process. Upon electrochemical oxidation the mediator violuric acid forms a radical with a lifetime on the order of several tens of minutes which oxidizes the lignin. During this step the mediator is recovered and easily separated from the pulp by filtration. The quality of the delignified pulp is remarkable due to the very high selectivity of the violuric acid radical in the oxidation of lignin over cellulose. Due to the extended radical lifetime in water the external radical generation in an electrolyzer enables the integration into existing setups. In a lab-scale demonstrator the EMB process was modeled. It was observed that there is a loss of mediator due to secondary reactions in the process. This much more determines the total costs than the price for the mediator itself. The different side products have been quantitatively analyzed and their origins have been identified. This will enable a further optimization of the EMB process. (C) 2003 The Electrochemical Society.