The degradation and mineralization of 3-indole butyric acid (IBA) in aqueous solution was examined using Fenton and Fenton-like processes. Various operating conditions were evaluated including pH and the concentrations of iron ions (Fe(2+) and Fe(3+)) and hydrogen peroxide (H(2)O(2)). The highest COD removal efficiency was achieved at 0.2 mM/0.6 mM Fe(2+)/H(2)O(2) ratio and 0.2 mM/1.0 mM Fe(3+)/H(2)O(2) ratio at pH 3 for Fenton and Fenton-like processes, respectively. IBA degradation and mineralization exhibited pseudo-first-order kinetics while the depletion of H(2)O(2) and Fe(2+) or Fe(3+) exhibited zero-order kinetics during both processes in all experiments. 97% of IBA degradation proceeded via two distinctive kinetic regimes. The initial phase of the reaction was directly attributable to the Fenton reaction wherein nearly all of the OH(center dot) radicals were generated. This was followed by a slower degradation phase, which can be thought of as a series of Fenton-like reactions within a Fenton process. In the Fenton-like process, the initial phase lasted longer than in the Fenton process because the generation of OH(center dot) radicals proceeded at slower rate; however, 98% degradation of IBA was achieved. The mineralization of IBA was 16.2% and 50% for Fenton and Fenton-like processes, respectively. After 24 h, H(2)O(2) was the limiting reagent for further mineralization of IBA intermediates present in the system. The results of the study showed that Fenton Process may be more useful when only removal of IBA is required and mineralization is unnecessary. But if mineralization of IBA is needed. Fenton-like process gains more important than Fenton Process due to its mineralization efficiency. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.