The influences of different chemical pre-oxidants, including sodium hypochlorite (NaClO), chlorine dioxide (ClO2), permanganate (KMnO4), hydrogen peroxide (H2O2), ozone (O3) and ozone/hydrogen peroxide (O3/H2O2), on chloral hydrate (CH) formation were studied for threonine that has the highest special chloral hydrate formation potential (SCHFP). Suitable pre-oxidants and corresponding optimal doses were determined to provide guidance for controlling chloral hydrate (CH) formation during drinking water treatment. The results indicated that the pre-oxidants that could decrease CH formation for one day incubation time (CH1d) were H2O2, ClO2, KMnO4 and NaClO, and the corresponding suitable doses were 3, 0.5, 0.6 and 0.5 mg·L-1, and the corresponding CH1d removal rates were 61.54%, 47.63%, 29.77% and 10.94%, respectively. The pre-oxidants that could decrease CH formation potential (CHFP) were KMnO4, NaClO, H2O2 and ClO2, and the corresponding suitable doses were 0.6 mg·L-1, 0.5 mg·L-1, 3 mg·L-1 and 0.5 mg·L-1, and the corresponding CHFP removal rates were 41.01%, 33.38%, 8.36% and 2.40%, respectively. In addition, O3 and O3/H2O2 were not suitable for controlling CH in the conventional treatment process because they could increase CH1d and CHFP.
Keywords: chemical pre-oxidation; chloral hydrate (CH); disinfection by-products (DBPs); precursor; threonine.