The Effect of Pre-Oxidation on Fractionation of NOM and DBPs Formation
Date Issued
2008
Date
2008
Author(s)
Lin, Hui-Chuan
Abstract
Natural organic matter (NOM) is a complex/heterogeneous mixture and is a major precursor of disinfection by-products (DBPs). Pre-oxidation with various advanced oxidation process (AOP) has been shown to be a good treatment technology to reduce NOM in water and to reduce DBPs. In this study, UV-H2O2 process and ozone treatment were chosen to remove NOM in water and the results were compared with the conventional water treatment processes. Since different NOM fractions had various potential to form DBPs and had different reactivity with oxidants, fractionation of NOM would be helpful to understand the properties of NOM further. The NOM was separated into four components: very hydrophobic acid (VHoA), slightly hydrophobic acid (SHoA), hydrophilic charged (HiC), and hydrophilic neutral (HiN) by a rapid fractionation method. The purpose of this study was to identify the portion of NOM that was more susceptible to certain oxidation process, and to find out the relationship between the NOM fraction and the DBP formation potential. The results showed that composition of NOM fraction were very different between various water sources, and the raw water quality in Kinmen was very special when compared to other source waters. Raw water taken from Kinmen generally had high DOC concentration and 50% of the NOM in Tai-lake raw water was hydrophilic because of severe pollution and eutrophication status. The hydrophobic fractions (VHoA, SHoA) were transformed into hydrophilic ones (HiC, HiN) after UV-H2O2 process or ozonation treatment. Both oxidation methods could effectively break the chemical bonding of NOM, but the UV-H2O2 process had better ability to mineralize NOM. After longer contact time with the oxidants, the DOC concentration of HiN portion increased in all water samples except in Kinmen raw water due to the extremely high DOC value in Kinmen’s raw water. In conventional treatment processes, coagulation and slow filtration had better effectiveness to reduce NOM in water especially for VHoA portion. Pre-chlorination increased the DOC concentration due to the degradation of some insoluble organic matters and the lysis of algae cells. The fractionation analysis showed that most of the organic compounds released are belong to VHoA and HiC fraction. The results of this study concluded that VHoA fraction was the most sensitive portion of NOM to UV-H2O2 process, ozone oxidation and conventional treatment processes. It was also the main contributor to THM formation after chlorination process.
Subjects
Nature organic matter
Disinfection by-product
UV-H2O2 process
Fractionation
Pre-oxidation
Type
thesis
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