【作者】 王哲；

【导师】 陈忠林；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2015， 博士

【摘要】 面对日益严重的水环境污染,常规的饮用水处理工艺某些时候已难以满足要求。以膜过滤技术和高级氧化技术为代表的新型饮用水处理技术开始受到人们的关注。膜过滤技术和高级氧化技术均因成本过高而难以大规模应用。其中,膜过滤技术中的膜成本和高级氧化技术中的催化剂成本是制约技术发展的关键。因此需要开发出廉价而高效的膜和催化剂。本文以廉价的硅酸盐水泥和石英微粉为原料,在室温环境下制备出一种低成本、平板型硅酸盐复合基微滤膜。考察了制膜过程中各工艺参数对膜的影响,进而优选出制膜的最佳工艺条件。通过扫描电镜分析、孔径分析、能量色散X射线光谱分析等手段,研究了硅酸盐复合基微滤膜的膜孔形成机制,并对膜的结构、组成和应用性能等进行了深入的表征和分析。本文还将制备的硅酸盐复合基微滤膜作为一种新型催化剂来催化臭氧降解水中有机污染物。考察了臭氧-膜联用工艺去除水中对氯硝基苯(p-CNB,p-chloronitrobenzene)的效能和机理。通过对膜制备过程中成型压力、颗粒粒径、水与硅酸盐水泥比例(w/c)、造孔剂和熟化方式等的考察,确定了制膜的各工艺参数为:成型压力6 MPa,石英粒径40.6-50.0μm,硅酸盐水泥粒径14.6μm,w/c 0.4,20℃、95%相对湿度的空气中熟化12天。依此条件制备的硅酸盐复合基微滤膜可以实现2.3μm的平均孔径,34%的孔隙率,13 m3?m-2?h-1?bar-1的纯水通量和4 MPa的抗弯强度。该条件下膜的孔径只呈现出双峰分布的特点。通过降低制膜所用石英与硅酸盐水泥的比例(q/c)至2.0,成功将膜的孔径分布由双峰分布改善为单峰分布。并依据该过程中膜孔的变化情况,分析出膜内微米级通透孔的形成机制。硅酸盐复合基微滤膜内的通透孔按成因大体可概括为三类。第一类是孔径7-8μm的膜孔,主要通过膜内石英颗粒的堆积作用而形成;第二类膜孔的孔径大体分布在1-3μm,是膜内占最大比例的膜孔,这类孔主要来源于硅酸盐水泥颗粒的堆积作用。第三类膜孔的尺寸大多在1μm以下,其孔的形成主要来源于膜内大量生长的针状钙矾石对大孔径膜孔的切割作用。通过将膜内q/c的值控制在2.0,不仅优化了膜的孔径分布,还使膜的抗弯强度提升到5-6 MPa,此时膜的平均孔径仅为1μm,膜孔隙率和纯水通量的结果也能满足要求。以筛选出的制膜条件制备硅酸盐复合基微滤膜,并对膜的结构和性能进行了深入的研究。对膜的结构表征发现,膜内的硅酸盐水泥在发生水化反应后,主要的水化产物为水合硅酸钙聚合物,在膜内呈胶凝状分布。其他产物还包括平板状的氢氧化钙,针状或薄片状的钙矾石等。硅酸盐复合基微滤膜的膜孔包含微米级孔和介孔两部分,其中微米级膜孔的孔体积在膜内占绝对优势。膜内微米级膜孔的平均孔径为1μm,介孔的平均孔径为13.5 nm。对膜性能的研究发现,硅酸盐复合基微滤膜具有与传统陶瓷膜相近的气液通量,对5×107个/L浓度的小球藻和10 NTU浊度的无机颗粒均可实现80%以上的去除。其中对小球藻的去除更有优势。但在膜污染方面,膜的藻类污染却比无机污染更难被清除。进一步的性能表征发现,硅酸盐复合基微滤膜可以承受500℃的热处理和0.01mol/L的碱腐蚀,在水环境中使用可保证水质的安全和膜的稳定。将制备的硅酸盐复合基微滤膜用于催化臭氧降解水中的有机污染物p-CNB。结果发现,在连续流实验中,臭氧-膜联用工艺可以有效去除水中p-CNB。与单独臭氧氧化工艺相比,在联用工艺中超过1.5 mg/L的溶解态臭氧被分解,致使p-CNB的去除率提高了50个百分点,而膜本身对p-CNB的吸附去除却可以忽略不计。电子顺磁共振波谱(EPR)实验和叔丁醇影响实验证明,臭氧-膜联用工艺对单独臭氧氧化过程的强化源于体系内羟基自由基的产生,膜孔表面存在的碱性水化产物和金属氧化物可能是促进羟基自由基生成和提升p-CNB去除率的关键因素。臭氧-膜联用工艺可以在多种水质条件下保证p-CNB的有效降解,且降解产物的毒性均小于p-CNB,这说明本文制备的硅酸盐复合基微滤膜除了具备截留能力外,还是一种廉价、高效的臭氧催化剂。此臭氧-膜联用工艺可作为一种应对水体突发有机污染的廉价应急处理技术。更多还原

【Abstract】 Water pollution is becoming a much severer issue. Traditional drinking water treatment process has been unable to meet the requirement of water quality. Therefore, researchers has paid more attention on some new drinking water treatment processes, such as membrane filtration and advanced oxidation process. However, the membrane filtration technology and the advanced oxidation process are not suitable for large-scale water treatment processes because of their high cost. The cost of membrane and catalyzer in these technologies are critical factors. Thus, developing some novel membranes and catalyzers with high efficiency and low cost is necessary.A new plate silicate composite based microfiltration membrane was fabricated using low-cost cement and quartz under room temperature. Multiple membrane fabrication parameters were studied and an optimum condition was screened out. Moreover, pore formation mechanisms of the membrane was confirmed using scanning electron microscope(SEM), pore size analysis and energy dispersive X-Ray spectroscopy(EDX). After that, the membrane was characterized from the point of membrane structure, membrane composition and application performance. Also, the fabricated membrane was used to catalyze dissolved ozone and degrade p-chloronitrobenzene(p-CNB) in aqueous conditions. In this process, the p-CNB degradation efficiency and mechanisms were studied.By a deep analysis of membrane fabricaiton processes, some membrane fabrication parameters were fixed. For example, 6 MPa of membrane forming pressure, 40.6-50.0 μm of quartz particle size, 14.6 μm of cement particle size, 0.4 of water-to-cement ratio, 12 days of membrane curing under 20℃ and 95% of relative humidity. Based on above conditions, a silicate composite based microfiltration membrane could be produced with 2.3 μm of mean pore size, 34% of porosity, 13 m3?m-2?h-1?bar-1 of water flux and 4 MPa of bending strength. However, it must be pointed out that membrane pore size distribution was imperfect under this conditions. The fabricated membrane just showed a bimodal pore distribution.By decreasing quartz-to-cement ratios(q/c) to 2.0 in the membrane fabrication process, the membrane pore size distribution was successfully optimized from a bimodal distribution to a unimodal distribution. Based on above pore size changement, pore formation mechanisms of the membrane was confirmed. In the membrane, three types of pores(I, II and III) were formed:(1) The formation of type I pores(with 7-8μm of pore size) was mainly attributed to the stacking of quartz particles;(2) The formation of type II pores was mainly attributed to the stacking of cement particles. Type II pores occupied most of pores in the membrane and mostly had a pore size of 1-3 μm;(3) Type III pores were less prevalent than type II pores and mostly had a pore size of below 1 μm. The formation of type III pores was attributed to the division of bigger pores by the thin needle-like ettringite. In the membrane producing process, using 2.0 of q/c not only optimized the pore size distribution, but also increased membrane bending strength to 5-6 MPa. Moreover, the target membrane had a mean pore size of 1 μm. Membrane porosity and water flux could also be accepted.A deep characterization of the optimized membrane was carried out from the point of membrane structure and performance. By characterizing membrane sructure, polymeric calcium silicate hydrate was proved to be the main composition of multilple cement hydration byproducts, which excited in gel state in the target membrane. Other cement hydration byproducts were also observed, such as plate calcium hydroxide, needle-like ettringite and sheet-like ettringite. A detailed pore analysis confirmed that membrane pores were in two size grade: micron scale pores and nano scale pores. The micron scale pores were dominant in the membrane with a mean pore size of 1μm. The nano scale pores had a mean pore size of 13.5 nm. By analysizing membrane performance, the fabricated membrane was found to obtain an acceptable gas and water flux, compared with traditional ceramic membrane. Membrane rejection study confirmed that more than 80% of Chlorella vulgaris and inorganic particles were stopped by the membrane used. And the removal of Chlorella vulgaris showed better. However, membrane fouling from the Chlorella vulgaris were more difficult to clean, compared to the inorganic fouling. A further study of membrane performance presented that the silicate composite based membrane could bear 500℃ of heat treatment and 0.01 mol/L of alkaline corrosion. It had the ability of operation to ensure water security and membrane stability.The fabricated silicate composite based membrane was futher applied to catalyze dissolved ozone and degrade p-chloronitrobenzene(p-CNB) in aqueous conditions. Results indicated that, the hybrid ozone-membrane process successfully increased the degradation efficiency of p-CNB compared with the ozone-alone process under continuous flow. The ozone-membrane process decomposed 1.5 mg/L of dissolved ozone and increased the p-CNB removal by 50% with little adsorption. The results of electron paramagnetic resonance(EPR) and tert-butanol affection experiments confirmed that p-CNB degradation followed the mechanism of hydroxyl radical oxidation during the ozone-membrane process. The alkaline hydration products and metal oxides appeared on the surface of membrane pores possibly promoted the hydroxyl radical generation and enhanced the p-CNB degradation. The hybrid process was observed to maintain the ability of removal p-CNB efficiently in different water sources. Moreover, The toxicity of the degradation byproducts were also less than p-CNB. Therefore, the membrane used was an low-cost but efficacious catalyzer for ozonation process. And the hybrid ozone-cementitous membrane process could be used as a kind of emergency treatment technology to deal with some sudden organic pollutions in water.更多还原