In this paper, the degradation of azo dye Acid Orange 7 (AO7) by three common peroxides (persulfate (PS), peroxymonosulfate (PMS) or hydrogen peroxide (H2O2)) under various activation conditions, i.e., heat (25-80 degrees C), UV light (254 nm), or anions (SO42-, NO3-, CO32-, HCO3-, HPO42-, and Cl-), was investigated. The order of AO7 degradation efficiencies by heat activation is PS >> PMS > H2O2. PS oxidation activated by heat (>50 degrees C) is an effective degradation technology, while PMS and H2O2 are hardly activated. When assisted by UV, peroxides could all be activated and degrade AO7 quickly. The order is PS > H2O2 > PMS. We activated peroxides, for the first time, by using some anions and compared the subsequently degradation efficiencies of AO7. It was found that PMS could be activated by some anions, but PS and H2O2 cannot. The activation efficiencies of PMS by SO42- and NO3- are negligible, whereas remarkable by HCO3-. HPO42-, Cl-and CO32-. For HCO3-, HPO42- and C-l-, the activation efficiencies become higher with the increase of anion concentration. For CO32-, however, the activation efficiency is higher at lower concentration. (C) 2010 Elsevier B.V. All rights reserved.