Four advanced oxidation processes (UV/TiO(2), UV/IO(4)(-), UV/S(2)O(8)(2-), and UV/H(2)O(2)) were tested for their ability to mineralize naphthenic acids to inorganic carbon in a model oil sands process water containing high dissolved and suspended solids at pH values ranging from 8 to 12. A medium pressure mercury (Hg) lamp was used, and a Quartz immersion well surrounded the lamp. The treatment goal of 5 mg/L naphthenic acids (3.4 mg/L total organic carbon (TOC)) was achieved under four conditions: UV/S(2)O(8)(2-)(20 mM) at pH 8 and 10, and UV/H(2)O(2) (50 mM) at pH 8 (all with the Quartz immersion well). Values of electrical energy required to meet the treatment goal were about equal for UV/S(2)O(8)(2-) (20 mM) and UV/H(2)O(2) (50 mM) at pH 8, but three to four times larger for treatment by UV/S(2)O(8)(2-) (20 mM) at pH 10. The treatment goal was also achieved using UV/S(2)O(8)(2-) (20 mM) at pH 10 when using a Vycor filter that transmits light primarily in the mid and near UV, suggesting that that treatment of naphthenic acids by UV/S(2)O(8)(2-) using low pressure Hg lamps may be feasible. (C) 2011 Elsevier B.V. All rights reserved.