Oxidation reduction potential (ORP) changes were monitored during the course of the remediation of four wastewater matrices by metallic iron (Fe-0) based on a batch fluidized bed reactor. Two of these matrices contained azo dyes (Acid Orange II and Acid Blue 113), another contained pentachlorophenol and the fourth was an authentic dyewaste. For the azo dye Acid Orange II ORP was found to follow the same trend as the dye concentration ([AOII]), decreasing exponentially with time over the course of the remediation. Change in ORP was found to be directly proportional to [AOII] and to follow a logarithmic relationship with [Fe2+](2)[aa](2)[AOII](-1), indicating a Nernstian behaviour. It is concluded that the ratio of remediation products to reactants can be determined directly by monitoring changes in ORP. The electrochemical conditions that influence corrosion were found to control remediation, consistent with the remediation being driven by anaerobic corrosion and predicted from potential-pH Pourbaix diagrams.