Disclosed is a system for renovating process water, especially during the production of paper. Said system comprises at least one process water renovation unit, at least one of which is provided with an anaerobic reactor spiked with anaerobic microorganisms as well as a lime elimination unit. Also disclosed is a method for renovating process water, particularly during the production of paper, which encompasses at least one process water renovation step in which at least some of the process water continuously delivered to the process water renovation step is subjected to a purification step in an anaerobic reactor that is spiked with anaerobic microorganisms and to a deliming step.