In this work, the biologically pre-treated leachate was subjected to catalytic micro-ozonation using cow dung ash composites loaded with Fe3O4 nanoparticles (nano-Fe3O4@CDA) as the catalyst. The optimal conditions used were nano-Fe3O4@CDA dosage of 0.8 g/L, input ozone of 3.0 g/L, and reaction time of 120 min. This environment yielded the following results: The COD and color number (CN) removal reached 53% and 89%, respectively, and the BOD5/COD increased from 0.05 to 0.32. The catalytic micro-ozonation partially degraded the refractory substances into intermediates with lower molecular weight. The percentage of phenolic compounds decreased sharply from 28.08% to 8.56%, largely due to the opening of the ring as well as to the formation of organic intermediates with a low molecular weight. Based on the results culled from the electron paramagnetic resonance (EPR), it is evident that the nanoFe(3)O(4)@CDA catalyst can accelerate in order to generate (OH)-O-.. This was the main mechanism involved in its excellent ability to degrade refractory pollutants. These results demonstrated the potential use of nanoFe(3)O(4)@CDA as a catalyst in the catalytic micro-ozonation process. (C) 2018 Elsevier Ltd. All rights reserved.