The influence of UV/H2O2 on organic carbon and nitrogen precursors and disinfection by-products formation in drinking water
Date Issued
2011
Date
2011
Author(s)
Chen, Huei-Wen
Abstract
The presence of various organic contaminants in water sources is of concern due to their direct threats to human health and potential to react with disinfectants to form carcinogenic byproducts including trihalomathanes, haloacetic acids and nitrosoamines in water disinfection process. Ultraviolet light coupled with hydrogen peroxide (UV/H2O2) is a powerful water treatment technology by forming highly reactive hydroxyl radicals. This study examined the relationships between organic matter compositions and disinfection by-product formation potential (DBPFP) by two major aspects. First, laboratory synthetic water with various compositions of organic carbon and nitrogen were treated with UV/H2O2 to evaluate its degradation efficacy. Second, both high-pressure and low-pressure ultraviolet light were applied to evaluate its efficacy for degradation of six selected nitrogenous organic compounds. After UV/H2O2 oxidations, corresponding disinfection byproducts (DBPs) formation potentials were measured.
In laboratory synthetic water, it was found that carbon containing precursors were relatively easier to mineralize by UV/H2O2 treatment than the nitrogen containing compounds. UV/H2O2 processes successfully reduced the precursors of trihalomethanes (THMs) and haloacetic acids (HAAs); however, the treatment efficiency was lower for N-nitrosodimethylamine (NDMA) precursors. It was also observed that the degree of precursor removal was reduced when raw water was contaminated by domestic wastewater effluents. In comparison to untreated water, UV/H2O2 treated water produced a higher ratio of HAAs than THMs after chlorination. This suggests that a higher fraction of hydrophilic compounds was obtained after UV/H2O2 treatment. Raw water impaired by wastewater effluent also altered the formation and species distribution of DBPs, since higher ratio of HAAs and brominated DBPs were observed.
With higher oxidation power and simpler molecular structure, target compounds resulted in better reduction of organic matters and DBP formation potentials (DBPFPs). However, insufficient contact time and oxidant doses could lead to a rise of DBPFPs in the early stages of UV/H2O2 reactions. A greater percentage removal was achieved for organic carbon than organic nitrogen after UV/H2O2 treatment, especially for complex compounds such as diltiazem. During the UV/H2O2 treatment, the intermediate products include tertiary amine, dimethyl amine (DMA) or DMA-like structures, which are N-nitrosodimethylamine (NDMA) precursors after disinfection. Furthermore, it was observed that using dissolved organic nitrogen and DMA to predict NDMA formation potential could lead to biased conclusions because of the complex nature of nitrogenous matters in aqueous environments.
Subjects
DOC
DON
THMFP
HAAFP
NDMAFP
SDGs
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