Effects of UV/PS and UV/H2O2 pre-oxidations on the formation of trihalomethanes and haloacetonitriles during chlorination and chloramination of free amino acids and short oligopeptides

• UV/PS presented better performance on controlling HAN formation than UV/H2O2.
• UV/PS somewhat increased THM formation from AA chlorination, but UV/H2O2 did not.
• UV/PS and UV/H2O2 did not obviously alter the DBP formation prior to chloramination.
• More bromine was incorporated into DHANs than into THMs from combined AAs.
• UV/PS decreased the formation of brominated DBPs, but UV/H2O2 did not.

Free amino acids (AAs) can form trihalomethanes (THMs) and haloacetonitriles (HANs) during chlorination in drinking water treatment plants, but they account for a small fraction of dissolved organic nitrogen (DON) pool in natural waters. In contrast, combined AAs contribute to a greater identifiable DON portion, but the information on the formation and control of THMs and HANs from them is limited. Ultraviolet/hydrogen peroxide (UV/H2O2) and ultraviolet/persulfate (UV/PS), two typical UV-based advanced oxidation processes (UV-AOPs), are both promising drinking water technologies for the reduction of trace organic contaminants. The objective of this study is to examine the effects of the two UV-AOP pre-treatments on the formation of carbonaceous and nitrogenous disinfection by-products (C- and N-DBPs), which were indicated by THMs and HANs, respectively, during post-chlorination and chloramination of tyrosine (Tyr) in free and combined forms. Results showed that direct UV photolysis, PS pre-oxidation alone or H2O2 pre-oxidation alone did not significantly impact the THM and HAN formation during subsequent chlorination. However, the two UV-AOP pre-treatments could somewhat alter the DBP formation. In general, under the identical doses (UV irradiation dose and molar oxidant dose), UV/PS pre-treatment better controlled the HANs than UV/H2O2 during AA post-chlorination, though UV/PS might slightly promote the formation of chloroform. In contrast, the two UV-AOP pre-treatments did not obviously affect the THM and HAN formation when post-chloramination was applied. In addition, a marked difference was observed in the speciation of DBPs formed from free AAs and short oligopeptides in the presence of bromide. For free Tyr, more brominated THMs were formed than brominated HANs; but for short oligopeptides, more bromine was incorporated into HANs than THMs.

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