Degradation of p-nitrophenol (PNP) by electrolysis, ozonation, and their combined processes (electrolysis-O-3) was investigated. While electrolysis degraded PNP completely in 6 h, it produced considerable amounts of polymer by-products (similar to 20% of the total organic carbon (TOC) of the original solution). By comparison, ozonation and electrolysis-O-3 degraded PNP much faster (in similar to 30 min) and produced no detectable polymers. TOC analyses showed that the combined eletrolysis-O-3 process mineralized PNP and its degradation intermediates much more effectively (98% TOC removal at 1.5 h) than the individual electrolysis and ozonation processes (58% and 75% at 6 h, respectively). Combining electrolysis with ozonation can thus not only inhibit polymer formation during electrochemical degradation of PNP, but also enhance pollutant mineralization significantly. The results indicate that the combination of electrolysis and ozonation can provide a simple and effective way to improve the performance and efficiency of existing electrolysis and ozonation systems for phenolic wastewater treatment. (C) 2014 Elsevier B.V. All rights reserved.