Influencing pathways and toxicity changes of pre-ozonation on carcinogenic NDEA formation from greenhouse gas adsorbent DEAPA in subsequent disinfection processes.

This study was to evaluate the feasibility of controlling carcinogenic nitrosodiethylamine (NDEA) formation from greenhouse gas adsorbent 3-diethylaminopropylamine (DEAPA) by pre-O3 in subsequent chlorination/chloramination processes. The result indicated that the NDEA yields (0.4 %) during chlorination was 1.3 times of that during chloramination (0.3 %); pre-oxidation with 4 mg/L O3 significantly cut down its formation; the reduction rates were up to 67.5 and 48.5 %, respectively. OH scavenger greatly augmented the final NDEA amount from 1.86 to 5.05 µg/L during ozonation, while its roles on subsequent processes differed with disinfection methods as well as O3(g) dosages. Most of co-existed substances inhibited NDEA generation, except NO2-, CO32- and SO42-, which slightly promoted during ozonation. Basing on Gaussian calculation, GC/MS and UPLC-Q-TOF-MS analysis, the influencing mechanisms of pre-O3 on NDEA formation in subsequent disinfection processes were proposed. In addition, the calculated toxicity analysis as well as the whole toxicity was applied to evaluate the possibility of pre-O3 on risk control.

Exploring Br-'s roles on non-brominated NDMA formation during ozonation: Reactive oxygen species contribution and brominated intermediate path validation.

Bromide ions (Br-) affected non-brominated nitroso-dimethylamine (NDMA) formation during ozonation, but the mechanism is still unclear. 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene) di-semicarbazide (TMDS) was chosen to further probe this problem. The results indicated that low levels of Br- (≤20 µM) enhanced NDMA from 3.27 to 7.56 µg/L, while its amount slightly dropped to 6.22 µg/L raising Br- to 100 µM. It was experimentally verified that intermediates 1,1-dimethylsemicarbazide (DMSC) and 1,1-dimethylhydrazine (UDMH) played important roles on promoting NDMA generation, whose contribution rates were 40.2% and 32.2%, respectively. The brominated substances with higher NDMA molar yields were detected. ∙OH reduced NDMA formation without Br-, while it played promotion role with Br-; the corresponding contribution rates were - 26.9% and 29.2%, respectively. No matter with or without Br-, both ∙O2- and lO2 brought a boost to NDMA formation, their contribution ratios were 34.9% and 58.1% without Br-, while raised significantly to 64.6% and 81.5% when Br- existed. Br- not only facilitated NDMA formation, but also benefited the degradation of TMDS. Based on the calculation results and intermediates detected, the influence mechanisms of Br- were proposed. The results would provide theoretical basis and technical guarantee for treating NDMA precursors and bromide co-existing water in the future.