Peracetic acid (PAA) is gaining increased acceptance among chlorine-alternative chemical disinfectants claiming that only harmless disinfection by-products (DBPs) have been identified so far, most of them arising from its spontaneous decomposition. A pilot study has been undertaken, using a 10m(3)/h pilot plant fed by municipal secondary settled effluent, in order to assess possible formation of unhealthy DBPs following its use, namely aldehydes and halogenated phenols. Negligible amount of both DBP classes was found in the experimental conditions investigated. Additionally, halogenating phenol reaction products and aldehydes formation were evaluated by carrying out a laboratory set of model reactions permitting to draw some light on mechanism of potential formation of aldehydes and brominated phenols.