The degradation of acetaminophen (APAP) in UV/TiO2, UV/H2O2 and UV/PS system was evaluated in study. Hydroxyl radical (OH center dot) was identified in quenching tests to be responsible for acetaminophen degradation in UV/TiO2 and UV/H2O2 systems, whereas sulfate radical (SO4-center dot) was in UV/PS system. The acetaminophen decay exhibited a pseudo-first-order kinetics pattern in different conditions, including initial acetaminophen concentration, oxidant or catalyst dosage, pH(0) and anions (carbonate and chloride). The pseudo-first-order degradation rate constant (k(obs)) in LIV/TiO2, UV/H2O2 and UV/PS systems exhibited an exponential trend as a function of [APAP](0) and followed the order at the same [APAP](0): UV/H2O2 > UV/PS > UV/TiO2. The k(obs) in UV/H2O2 and UV/PS system was determined to be positively proportional to initial oxidant dosage as koos = 0.00584 [H2O2](0)[AP] and k(obs) = 0.00436 [PS](0)[AP] respectively. The maximum k(obs) of (0.58 +/- 0.01) x 10(-2) min(-1) was obtained at pH = 7.0 for UV/H2O2 system, whereas the minimum k(obs) of (0.13 +/- 0.01) x 10(-2) min(-1) was found at pH = 7.0 for UV/PS system. For UV/TiO2 system, the k(obs) decreased slightly from (0.72 +/- 0.02) x 10(-2) min(-1) to (0.50 +/- 0.01) x 10(-2) min(-1) as pH increased from 3.0 to 11.0. The electrical energy per order (EE/O) values considering the chemical cost in three systems was demonstrated: UV/TiO2 (0.0256 kWh/m(3)/order) > UV/PS (0.0184 kWh/m(3)/order) > UV/H2O2 (0.00146 kWh/m(3)/order). According to the results in the study, co-existing anions affect the degradation in various degrees for three systems, thus co-existing anions should be seriously taken into consideration on the selection of degradation system. (C) 2014 Elsevier B.V. All rights reserved.