Green ContextThe development of more environmentally benign alternatives to chlorine in pulp bleaching processes is an important large scale industrial challenge—Redox mediators and more recentlyN-hydroxy compounds have been proposed for this purpose. They generate radicals in the presence of enzymes, and these in turn cause pulp delignification. Unfortunately, significant quantities of these ‘mediators’ are lost in the delignification process. This paper analyses this loss, explains its cause and thus opens the door to improved mediator design. Thus electrochemical mediator-based delignification is shown to be an attractive alternative to existing chlorine-based processes.JHC