A modified Nernst equation was used to describe the decoloring reaction using the Oxidation-reduction potential (ORP) as an on-line monitoring and control parameter of the chemical reaction. In the modified equation, an ''S'' term is defined to indicate the oxidative potential (or decoloring potential) of dyes being studied. The laboratory study utilizes sodium hypochlorite (NaOCl) to reduce the color of wastewater spiked with textile dyes. Five dyes were used in preparing the wastewater samples : methyl red (MR), methyl violet (MV), methyl blue (MB), malachite green (MG) and methyl orange (MO). The color was measured by use of an automatic ADMI (American Dye Manufacturer Institute) measurement system in which a visible spectrophotometer was connected to a personal computer and the samples were scanned from 400 nm to 700 nm with a 10 nm interval each step. During the batch decoloring studies, several factors including ADMI, ORP, temperature and pH were continuously monitored with the computer. In this study, the potential of the decoloring compound of the dyes studies are in the following order : MG>MV>MO>MR>MB, with numeric ratios of 2.08 : 1.78 : 1.78 : 1.28 : 1.00, respectively. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.
