标题: | 光触媒氧化及不织布薄膜过滤复合系统:分解特性及过滤行为之探讨 Hybrid system of photocatalytic oxidation and non-woven membrane filtration:photodegradation characteristics and filtration behavior |
作者: | 洪仁阳 Horng, Ren-Yang 黄志彬 Huang, Chih-Pin 环境工程系所 |
关键字: | 光触媒;光触媒薄膜复合系统;不织布薄膜;过膜压力;通量;比通量;Photocatalysis;Photocatalytic Membrane Reactor;Non-woven membrane;TMP;Flux;Specific Flux |
公开日期: | 2008 |
摘要: | 悬浮式光触媒氧化系统具有提供大量有效表面积、简化光源配置及无需固定光触媒等优点,但如何有效且经济地分离并回用光触媒,仍是环保界亟待解决的重要课题。本研究从材料选择、系统建立及验证等方面着手,希望发展一种新颖性的光触媒及薄膜复合系统。 本研究以不织布薄膜(或称巨孔薄膜)取代一般使用微孔薄膜的光触媒薄膜复合系统(photocatalytic membrane reactor, PMR),由其材质特性分析进而探讨不织布薄膜之过滤行为。并就不同目标污染物如亚甲基蓝、4-氯酚及二级放流水等进行污染物光分解特性研究及应用可行性验证,以探讨光触媒及不织布薄膜复合系统建立之可能与效能。 首先,藉由不织布材质结构特性分析,并进行最佳不织布薄膜筛选的研究。采用0.2、2.0及20.0 µm等三种不同孔洞之不织布薄膜,并以比通量及滤液残留浊度为指标。实验发现,选用2.0 µm不织布薄膜,使其孔洞大小略等于或小于凝聚后光触媒颗粒(或称二级颗粒)(约2-8 µm)时,能有效地分离光触媒,并同时可以符合上述两项指标需求。 其次,由于不织布薄膜的过滤阻抗(filtration resistance)会受操作条件如光触媒浓度、pH值、空气强度及操作通量等影响,尤其操作通量达3 m3/m2/day或更高时,过滤阻抗更为明显。由于不织布薄膜孔洞较大,且薄膜本身过滤阻抗极低,故其过滤阻抗以多孔性滤饼(cake formation)为主,约占80%,而可逆及不可逆之孔洞阻塞(pore blocking)或孔洞缩小(pore narrowing)之过滤阻抗相对较低,分别各占10%左右。本研究结果显示,上述过滤阻抗经由适当操作条件控制,可维持多孔性滤饼之厚度,进而获得较低的过膜压力及稳定操作通量。 接着,使用亚甲基蓝为目标污染物进行批次及连续实验以探讨光触媒及不织布薄膜复合系统的建立。在批次实验中,由于光分解目标污染物浓度低,可适用Langmuir -Hinshelwood反应动力之拟一阶反应动力之描述。连续实验中,槽中SS浓度随操作流量(或通量)增加而降低,且滤液SS浓度低于侦测极限值,被拦截的光触媒颗粒将在不织布薄膜表面形成多孔性滤饼。当过滤层形成后,配合适当操作条件,可获得相当低过膜压力(约3.5 kPa)及维持稳定操作通量。 最后,以4-氯酚及二级放流水为对象进行复合系统之应用研究,主要诉求为光触媒钝化及积垢物质之去除。在4-氯酚光分解过程中,发现氯离子生成并不会造成光触媒钝化或毒化现象,此与悬浮式光触媒系统可以提供大量表面积及适当操作条件如pH值及溶氧有关。另外,复合系统可以有效去除二级放流水之积垢物质如生物高分子及腐植酸等,进而大幅改善UF薄膜过滤性,有助于提升本复合系统之应用潜力。 综合上述讨论,本研究提出之光触媒氧化及不织布薄膜分离复合系统可有效分离悬浮光触媒颗粒及分解污染物,配合最佳孔洞不织布薄膜选用及其表面形成多孔性滤饼之过滤方式,可以获得低过膜压力与稳定操作通量,进而避免积垢现象发生。 A suspended photocatalytic oxidation system offers lots of active sites for photocatalytic oxidation, simplifies UV light arrangement, and obviates the complexities of fixing a photocatalyst onto a substrate. However, effective and economic separation of photocatalyst from the slurry system is still a problem to be addressed. In this study, a novel photocatalytic membrane reactor (PMR) has been developed based on material selection, system development, and application study. The non-woven membrane (or called macroporous membrane) instead of microporous membranes, e.g. MF or UF, was proposed in a PMR to separate photocatalysts from slurry and to photodegrade model compounds such as methylene blue, 4-chlorophenol, and secondary effluent. Three major parts including material characteristics of non-woven membrane and their filtration behavior, the development of the hybrid system from batch and continuous tests and the application studies of the hybrid system are emphasized in this study. Three different pore sizes of non-woven membrane, 0.2, 2.0, and 20.0 µm, were applied to determine the most optimum filtration performance in terms of specific flux and residual turbidity in permeate. The results showed that when the pore size of the non-woven membrane was equal to or smaller than that of secondary particles of photocatalyst, a high specific flux and low turbidity in permeate were obtained simultaneously. Therefore, a 2.0 µm pore size of the non-woven membrane was selected for further study. The filtration resistance in non-woven membrane was determined by the operating conditions, e.g. concentration of photocatalyst, pH value, air intensity and applied flux. The filtration resistance was more and more significant when applied flux was 3.0 m3/m2/day or more. Because the pore size of the non-woven membrane was large (i.e. 2.0 µm) and the filtration resistance from membrane itself was minor, the filtration resistance was dominated by porous cake formation, about 80%, and the rest of 20% was shared equally by reversible and irreversible pore blocking or pore narrowing. Under the circumstances, the thickness of porous cake formation was controlled by optimum operating conditions to obtain stable applied flux and low TMP. The photodegradation characteristics of methlyene blue and filtration behavior using a 2.0 µm pore size of non-woven membrane were demonstrated in batch and continuous modes. The photodegradation of methlyene blue followed by pseudo-first-order reaction kinetics was proposed, because a low concentration of model compound was used. In continuous mode, the concentration of SS in hybrid system was decreased with increasing flow rate (or applied flux) resulting in the formation pf porous cake layer on the surface of non-woven membrane. Then, TMP was maintained around 3.5 kPa under optimum air intensity to induce a crossflow velocity after cake layer was formed. The inactivation of photocatalyst and the photodegradation performance of organic fouling materials were focused on the application study of this hybrid system, when 4-cholophenol and secondary effluent were used, respectively. The inactivation or toxicity of photocatalyst was no obvious when the chloride ion was formed after photodegradation of 4-chlorophenol, because the tremendous active sites onto the surface of the suspended photocatalyst could offer and suitable operating conditions, e.g. pH value and dissolved oxygen, were performed. Moreover, organic fouling materials, e.g. biopolymer and humic acids, in the secondary effluent were photodegraded using this hybrid system to improve the filtration ability of UF membrane by a batch stirred cell test. Therefore, the proposed hybrid system in which a non-woven membrane could replace microporous membrane in a PMR system was used to separate completely suspended photocatalysts and to photodegrade effectively model compounds. At the same time, low TMP and stable applied flux in this hybrid system was expected to reduce dramatically membrane fouling potential after the optimum pore size of non-woven membrane was selected and the porous cake layer was formed on the surface of non-woven membrane. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT009419806 http://hdl.handle.net/11536/81230 |
显示于类别: | Thesis |
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