An actual mixed chemical wastewater was treated using internal electrolysis. A significant effect was observed, with an average chemical oxygen demand removal efficiency of 20%, a BOD5/COD enhancement efficiency of 80%, and an acute biotoxicity removal efficiency of 60%. These results show that the technology can be efficiently applied to refractory wastewater. The fillings were agglomerated after 50 days of operation. The pressure drop of the reaction sharply increased from 70 cm H2O to more than 100 cm H2O indicating that the fillings were agglomerated, and the performances of the process were simultaneously reduced. Various techniques were used for characterization to determine the mechanism of agglomeration. Scanning electron microscopy (SEM) shows granular matters on the surface of the fillings, which induced agglomeration. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results indicate that the granular matters were ferric hydroxide [Fe(OH)(3)] particles, which exhibited the amorphous crystal structure. XPS and Fourier transform infrared spectroscopy (FTIR) results indicate that the adsorption during the internal electrolysis process was via chemical adsorption, and Fe(OH)(3) could easily adsorb organic molecules containing electron-donating groups such as -CONH2, -COOH, and -CH3. The deposition of Fe(OH)(3) on the surface of the fillings and its subsequent adsorption of organic species were the primary cause of agglomeration in the internal electrolysis technology. (C) 2012 Elsevier B.V. All rights reserved.