THE POTENTIAL FORMATION OF HALOGENATED BY-PRODUCTS DURING PERACETIC-ACID TREATMENT OF FINAL SEWAGE EFFLUENT

The potential generation of halogenated by-products, during the treatm ent of final effluent using peracetic acid (PAA) is described. Phenol was used as a model compound as it is an excellent acceptor of free ra dicals, readily undergoing chemical transformation to produce halogena ted compounds. Increases in the concentration of monosubstituted chlor ophenols following PAA treatment were apparent. The chlorophenols appe ar to be rapidly generated upon contact with the PAA, although by-prod uct formation did not appear to be dependent on temperature or reactio n contact time. The concentration of by-products was however, influenc ed by PAA dosage, chloride content and the concentration of organic an d mineral constituents in the final effluent. It was demonstrated that PAA was unable to oxidise chloride to hypochlorous acid. It is theref ore 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 i n the effluent. The formation of 2- and 4-bromophenol demonstrated tha t the electrochemistry of PAA is, however, sufficient to oxidise bromi de to hypobromous acid and subsequently form brominated organics.