Aqueous chlorination of algal odorants: Reaction kinetics and formation of disinfection by-products

Bench-scale kinetics tests were conducted to evaluate the formation of disinfection by-products (DBPs), as well as the odorant degradation, during chlorination of representative algal odorants. β-Cyclocitral degradation better followed a pseudo first order kinetics pattern, while the decomposition behaviors of β-ionone and heptanal were better described by the pseudo second order kinetics. Trihalomethanes (THMs) were commonly found during chlorination of β-cyclocitral, β-ionone and heptanal, but dimethylsulfide and dimethyl trisulfide did not contribute to the THM formation. In contrast, haloacetic acids (HAAs) were undetectable in all the samples. During chlorination of β-cyclocitral, β-ionone and heptanal, primary intermediate oxidation products were identified. Particularly, β-ionone was a significant THM precursor. Typically, the formation of chloroform was favored with the increasing pH from 2 to 12. In the tests to chlorinate raw water collected from the Taihu Lake, China, odorants in Microcystis aeruginosa could contribute to the chloroform formation. β-Cyclocitral and β-ionone, accounting for 0.021% μg/μg DOC and 0.0027% μg/μg DOC of intracellular organic matter (IOM), produced 0. 98% and 0.78% chloroform of IOM formed, respectively. This study demonstrated that algal odorants played a critical role in the DBP formation during chlorination in water treatment.

► This is the first attempt to quantitate chloroform formation of algal odorants. ► Chlorination of dimethylsulfide and dimethyl trisulfide appeared not to produce THMs and HAAs. ► β-Ionone could produce ∼224 μg chloroform/mg, while β-cyclocitral formed ∼41 μg/mg. ► β-Cyclocitral and β-ionone had a relatively high contribution to chloroform from Microcystis aeruginosa.