The potential formation of halogenated by-products during peracetic acid treatment of final sewage effluent

The potential generation of halogenated by-products, during the treatment of final effluent using peracetic acid (PAA) is described. Phenol was used as a model compound as it is an excellent acceptor of free radicals, readily undergoing chemical transformation to produce halogenated compounds. Increases in the concentration of monosubstituted chlorophenols following PAA treatment were apparent. The chlorophenols appear to be rapidly generated upon contact with the PAA, although by-product formation did not appear to be dependent on temperature or reaction contact time. The concentration of by-products was however, influenced by PAA dosage, chloride content and the concentration of organic and mineral constitutents in the final effluent. It was demonstrated that PAA was unable to oxidise chloride to hypochlorous acid. It is therefore proposed that the transformation of phenol to chlorophenol occurs through the generation of free radicals, the initiation and promotion of which are dependent on the presence of other organic contaminants in the effluent. The formation of 2- and 4-bromophenol demonstrated that the electrochemistry of PAA is, however, sufficient to oxidise bromide to hypobromous acid and subsequently form brominated organics.