The degradation of triclosan (TCS) by MnFe2O4/PMS was investigated. The system was able to remove TCS in less than 20 min. Recycled MnFe2O4 was found to be more efficient than fresh MnFe2O4 for TCS degradation as a result of the alteration of Mn sites by peroxymonosulfate (PMS), leading to an extra degradation pathway where no oxidants are required. A modified treatment process is originally proposed in this study by preactivating the catalyst with PMS prior to the succeeding reactions, as the toxicity test showed that PMS may have a lethal effect on aquatic animals. The results showed that the preactivated catalyst provides satisfactory results with the total removal of TCS in 20 min at neutral pH, whereas the modified process minimizes the direct addition of PMS to the bulk solution and therefore the potential toxicity to the aquatic life forms.