前氧化處理程序對天然有機物組成及消毒副產物生成之影響

Abstract

天然有機物是一種複雜且不均質的混合物，也是生成消毒副產物主要的前驅物質。為了減少消毒副產物的生成，可藉由高級氧化方式將水中的天然有機物去除。本研究選擇UV-H2O2 光催化程序以及臭氧氧化程序兩種不同的高級氧化方式來去除水中的有機物，並進一步比較其與傳統處理流程對有機物之去除效率。由於天然有機物是由多種不同性質的物質所組成，而每種物質生成消毒副產物的能力以及對氧化劑的反應性皆有所差異。欲進一步了解天然有機物之特性，本研究利用樹脂將其分離成四個主要的成分：非常疏水性酸性物質 (very hydrophobic acid; VHoA)、稍微疏水性酸性物質 (slightly hydrophobic acid; SHoA)、親水性帶電物質 (hydrophilic charged; HiC)、親水性中性物質 (hydrophilic neutral ; HiN)，希望能觀察不同有機成分在經氧化反應後之變化情形和其生成消毒副產物潛能之關係。 天然有機物各成分之組成比例，依照水源的不同而有所差異。來自金門太湖之水體中溶解性有機碳濃度高達13.6 mg/l，其中親水性的部份佔了50%，顯示人為汙染嚴重且存在優養化問題。在經由UV-H2O2光催化程序或臭氧氧化後，疏水性的物質 (VHoA, SHoA)隨著反應時間逐漸降解為親水性的物質 (HiC, HiN)，而最主要被去除的部份為非常疏水性酸性物質。這兩種氧化方法皆能有效的破壞大分子物質之化學鍵結，但相較於臭氧氧化，UV-H2O2光催化程序能礦化較多存在水中的天然有機物。由於金門原水中所含親水性中性物質含量相當的高且組成較為複雜，能被降解的量大都於來自疏水性酸的貢獻，故隨著氧化時間的增加，此部份溶解性有機碳濃度下降。此結果和其他的水體有不同的趨勢。 相較於其他的傳統處理流程，混凝和慢濾程序對於有機物有較高的去除率，而所去除的大多為非常疏水性酸性物質。在經前加氯處理後水中溶解性有機碳濃度有上升的情形，主要來自於一些在水中不易溶解的物質及藻類被氯氧化之結果，而這類物質大多屬於非常疏水性酸性物質和親水性帶電物質。 由本研究中可推論光催化程序臭氧氧化及傳統處理流程主要去除的皆為水中非常疏水性的酸性物質，而這些物質也是形成三鹵甲烷最重要的前驅物質。

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.