【作者】 吴东海；

【导师】 尤宏；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2011， 博士

【摘要】 船舶压载水是现代远洋船舶航海安全和高效营运的保证,但是随之带来的外来有害生物入侵性传播已成为海洋面临的四大威胁之一,成为亟待解决的世界性的环境问题。现有的压载水处理技术都存在着一定的缺点,还没有一种单一方法能满足国际海事组织关于压载水处理的要求。UV/Ag-TiO₂和O₃是两种高效的水体消毒技术,二者联用可生成更多的氧化性自由基,提高处理效果。本文采用UV/Ag-TiO₂/O₃来对水体进行快速灭菌、杀藻,并对其灭活机理进行了探讨,为寻求一种有效的船舶压载水处理工艺提供理论依据。为研究复合工艺的可行性,首先考察了臭氧、紫外及紫外/臭氧各自灭菌性能。结果表明,紫外辐射和臭氧本身都具有较强的杀菌性能,二者的联合使用显著增强了杀菌效果,并在反应的初始阶段表现出了一定的协同作用。臭氧和紫外联用时,臭氧分解加速,生成的?OH相应增加,灭菌后细菌的光复活得到显著抑制。采用在纯钛表面阳极氧化法制备高效、耐冲击TiO₂催化剂,对制备条件进行了考察,并通过光化学沉积法对制备的TiO₂催化剂进行了载银改性,研究了其在UV-C辐射下的光催化灭菌性能和灭菌机理。结果表明,制备出的多孔TiO₂薄膜催化剂由锐钛矿型和金红石型TiO₂组成。随电压升高,金红石型的含量逐渐增多,微孔孔径增大,电流密度的适当增大,以及适当提高电解液浓度有助于提高UV/TiO₂灭菌性能。通过表面光沉积银修饰,可进一步提高薄膜光催化活性,银纳米簇在催化剂表面均匀细密分布。在1.0 mol/L硫酸溶液中,140 V,150 mA/cm2条件下制备的TiO₂薄膜,经3 g/L硝酸银溶液中载银修饰后光催化灭菌效果最佳。UV/Ag-TiO₂灭菌较单独紫外灭菌对细菌杀灭更彻底,细菌光复活减少。通过对过滤系统,臭氧投加方式,光源及光催化反应器的设计和选取,建立了以微孔过滤为前处理的UV/Ag-TiO₂/O₃复合船舶压载水处理系统和装置,并应用该系统对海水中大肠杆菌、粪肠球菌和溶藻弧菌等三种细菌以及杜氏盐藻、前沟藻属甲藻和三角褐指藻等三种海洋微藻进行灭活研究,测定杀灭效果,分析了相关影响因素的作用,并对反应过程中总残余氧化物（TRO）的生成,衰减及其持续灭活作用进行了测定,从而考察UV/Ag-TiO₂/O₃复合技术在处理压载水中的有效性和可行性。结果表明,UV/Ag-TiO₂和O₃均具有较强的杀菌性能,但UV/Ag-TiO₂对微藻灭活效果较差。UV/Ag-TiO₂/O₃复合体系较UV/Ag-TiO₂和O₃单独杀菌、哈尔滨工业大学工学博士学位论文灭藻效果均有较大提高,杀菌时在较短水力停留时间时更明显。紫外光强6.5 mW/cm2,臭氧投加量9.84 mg/L时,水力停留时间3.0 s时即可达到对水体的灭菌要求,对杜氏盐藻,前沟藻属甲藻和三角褐指藻的灭藻率分别可达0.92,0.60和0.57 log。UV/Ag-TiO₂/O₃复合体系中?OH可能对系统杀灭微生物起到了一定的辅助作用。臭氧投加量和紫外辐射强度对复合灭菌、杀藻有重要影响,随着臭氧投加量的增加,复合灭菌、杀藻效果显著提高。紫外辐射强度的增加以及在较高的pH值和较低的水温更有利于复合灭菌,海水中NH3浓度对灭菌效果影响不大。UV/Ag-TiO₂/O₃复合处理对海水的pH值基本没有影响,出水中TRO浓度随臭氧投加量的提高而增加,且在初始阶段衰减很快,而后变缓。较高初始浓度和较低的水温使TRO衰减更慢。20℃时,当初始TRO浓度大于2.89 mg/L时,出水中的残余活菌可在0.5 h内被全部杀灭。为对UV/Ag-TiO₂/O₃工艺的可行性和实用性进行更深入的分析,同时为处理不同水体时工艺参数的选择寻求依据,对UV/O₃和UV/Ag-TiO₂灭菌过程中细菌的死亡机理进行了探讨,并通过建立静态循环实验,减缓反应速率,研究了UV/Ag-TiO₂/O₃杀灭海水中细菌和微藻的机理,从微观的角度考察不同反应体系杀灭微生物的过程,确定各要素的作用。结果表明,单独紫外辐射对细菌细胞结构的破坏较轻,在细菌被杀灭时,细菌细胞表面未出现在明显损伤。UV/Ag-TiO₂较UV对细菌细胞结构的破坏有所加剧,可逐步破坏大肠杆菌细胞表层结构,使胞内物质发生外泄,但相对较缓慢。臭氧可对微生物细胞结构产生明显的破坏,而UV/O₃/Ag-TiO₂作用下的破坏程度更高,细胞膜脂质过氧化产物MDA含量迅速增多,K+和蛋白质大量泄漏,并降解微藻的叶绿素a。由此,在UV/O₃/Ag-TiO₂复合体系中,紫外辐射主要通过对微生物的DNA破坏来杀灭微生物,而臭氧则可对微生物的细胞结构产生不可逆的破坏。当紫外辐射下臭氧和Ag-TiO₂的联合应用,可对微生物进行双重破坏和杀灭,同时反应体系中?OH等活性基团及臭氧和海水反应后生成的氧化性物质均可对微生物的死亡起到一定的辅助作用。本文所建立的UV/Ag-TiO₂/O₃反应系统是一种新型的高级氧化船舶压载水处理体系。能在很短的水力停留时间内有效杀灭水体中的细菌、微藻等微生物,同时处理后出水在压载水舱中具有一定的持续灭活能力。设备体积小,安装容易,操作简单,可以解决船舶压载水处理的瓶颈问题,具有较大的理论意义和广阔的应用前景。更多还原

【Abstract】 Ballast water is water carried by ships to ensure the stability and maneuverability during transit. However, ships transporting ballast water between geographically isolated ports contribute to the spread of many aquatic species beyond their natural range limits, and it has been regarded as one of the four major risk factors that threaten global marine environmental safety. To prevent the introduction of potentially invasive species, ballast water management and treatment are essential.There are several established and under developing technologies available to be used for ballast water treatment. Unfortunately there is not a single method can reach the standard quality due to its own disadvantages. A combination of several methods result in high treatment efficiency compared with individual treatment, and has become the main direction of research to solve the problem of ballast water. The objective of this study was to evaluate the effectiveness of UV/Ag-TiO₂/O₃ treatment in preventing introduction of invasive species during the ballasting/deballasting process. The combination of photocatalyst with ozone system was established. The inactivation efficiency of UV/Ag-TiO₂/O₃ on bacteria and microalgae were studied, and their death mechanisms were investigated.To evaluate the feasibility of the UV/Ag-TiO₂/O₃ process, the bactericidal activities of ozone, UV irradiation and UV/O₃ process were researched firstly. Results indicated that both ozone and UV irradiation were effective for bacteria inactivation, and a significant enhancement for E. coli inactivation efficiency was obtained in the combined UV/O₃ process as compared with each individual unit process, especially in the initial phase of the reaction. In the ozonation under UV irradiation, the ozone was accelerated decomposed, and a larger number of hydrogen peroxide and hydroxyl radicals were produced, thereby accelerated the bactericidal reaction, repressing the bacteria photoreactivation after treatment.Secondly, an efficient and impact resistance photocatalytic nano-porous titanium dioxide film was prepared by anodic oxidation method in sulfuric acid solution, and was loaded sliver by photodeposition method. The effect of anodizing parameters （anodizing voltage, current density and electrolyte concentration） on the photocatalytic bactericidal activity of TiO₂ films was investigated. It showed that the titanium oxide film was mainly composed of anatase and rutile TiO₂. With the increasing of anodizing voltage, the content of rutile TiO₂ increased, and the average diameters of nano-holes enlarged. Propore increase of current density and suitable Ag loading could enhance the photocatalytic activity of TiO₂ film. When prepared at 140 V, 150 mA/cm2 in 1 mol/L sulfuric acid solution, and loaded silver in 3 g/L silver nitrate solution, the Ag-TiO₂ film had the best photocatalytic bactericidal activity. Compared with UV-C irradiation alone, the inactivation of E. coli by the UV/Ag-TiO₂ process was enhanced and the photoreactivation of the bacteria was much repressed.Then, different filtration and ozone dosing modes, light sources, and the photocatalytic reactors were analyzed, and the combination of photocatalyst with ozone system and equipment, which were used for ballast water treatment, were established. The effectiveness of filtration-UV/Ag-TiO₂/O₃ treatment in preventing introduction of bacteria （Escherichia coli, Enterococcus faecalis and vibrio alginolyticus） and microalga （Dunaliella salina, Amphidinium sp. and Phacodactylum tricornutum） in artificial seawater during the ballasting/deballasting process were evaluated.The effects of UV light intensity, ozone dose and raw water quality, were examined in this system, and the formation and decay of the initial total residual oxidant （TRO） was investigated.The results indicated that both UV/Ag-TiO₂ irradiation and ozonation were effective for bacteria inactivation. However, UV/Ag-TiO₂ irradiation was not effective for microalga inactivation and chlorophyll a degradation. Compared with individual unit processes with ozone or UV/Ag-TiO₂, the inactivation of bacteria and microalga by the combined UV/Ag-TiO₂/O₃ process were enhanced, especially in the initial phase of the reaction. With an initial ozone dose of 9.84 mg/L, a UV fluence rate of 6.5 mW/cm2, the required bacteria inactivation ratio would be obtained within a hydraulic residence time （HRT） of 3.0 s. When the HRT increased to 3.0 s, the detected inactivation efficiency of Dunaliella salina, Amphidinium sp. and Phacodactylum tricornutum were 0.92, 0.60 and 0.57 log, respectively. The ?OH that produced in the UV/Ag-TiO₂/O₃ system contributed partly to the disinfection of microorganisms. The ozone dose and UV light intensity had a significant influence on the disinfection efficiency. With the UV intensity and ozone dose increasing, the disinfection efficiency was improved. When the ammonia concentration ranged from 0.1 to 1.0 mg/L, the E. coli inactivation efficiency changed little. When the pH value ranged from 8.0 to 8.6, the disinfection efficiency increased with the pH value, while the temperature increased from 5℃to 20℃, the efficiency of disinfection decreased. Compared with the raw water （pH 8.0）, the pH value of the effluent that after treatment by UV/Ag-TiO₂/O₃ process changed little. The initial total residual oxidant （TRO） concentration was positively correlated with ozone dose, and resulted in faster decay rate for lower initial concentration. All TRO concentrations reduced rapidly at first and attenuate slowly as the duration increased. When the initial TRO concentration increased above 2.89 mg/L by adjusting the ozone dose, complete inactivation of E. coli was achieved within 0.5 h.In order to further investigate the feasibility and practicality of the UV/Ag- TiO₂/O₃ process for ballast water treatment, the death mechanism of bacteria and microalga during UV/O₃, UV/Ag-TiO₂ and UV/Ag-TiO₂/O₃ disinfection were studied. The results implied that UV irradiation was not effective for the destruction of bacteria cell structure. Exposed to the UV/Ag-TiO₂ irradiation, the E. coli cell wall and cell membrane were gradually decomposed, and resulted in the leakage of intracellular potassium ion （K+） and protein, however comparable slowly. Contrastly, the ozonation could make the microorganism’s cell structure destructed seriously, and the combination of photocatalyst with ozone enhanced this effect, the formation of malondialdehyde （MDA） and leakage of intracellular potassium ion （K+） and protein was notable, and the chlorophyll a concentration decreased immediately. Therefore, in the UV/Ag-TiO₂/O₃ system, the UV-C disinfection mainly via destroy the cell DNA, and the decomposition of cell structure, which is irreparable, is one of the important causes for microorganism death during ozonation. Moreover, the combination of ozonation and photocatalysis with Ag-TiO₂ thin film under UV-C irradiation may not only destroy the cell structure, but also induce the cell DNA damage, and resulted in the enhancement of disinfection efficiency.The combination of photocatalyst with ozone system that established in this paper is a new advanced oxidation process system for ballast water treatment. It has high efficiency for removal the target organisms, and the effluent has continuous and extended sterility effect. The size of the equipment is small, and easy to operate. Thus, it can be used to solve the bottleneck problem of the ballast water treatment, and has the theoretical significance as well as the bright application prospect.更多还原