Photolysis of free chlorine to hydroxyl radical by sunlight and ultraviolet irradiation for enhanced disinfection of chlorine-resistant waterborne pathogens

1236303DoddFree有效氯（FAC）仍然是世界范围内饮用水实践中使用最广泛的消毒剂。它便宜，易于作为消毒剂使用，便携，并且通常对实现各种水生微生物病原体的灭活非常有效。然而，众所周知，作为细小隐孢子虫、鸟分枝杆菌和贾第鞭毛虫等重要病原体的主要消毒剂，它是相对无效的。这导致了更有效的替代消毒剂的广泛采用，但通常需要更多的资金、设备和能源密集型替代消毒剂，如紫外线和臭氧。最近的研究结果表明，在常规氯化过程中，利用阳光或单色紫外线将FAC光解为羟基自由基、原子氧和臭氧等高活性氧化剂，实际上可以以相当低的成本实现氯抗性微生物病原体的失活。在这种方法中，FAC和光化学生成的氧化剂可以协同作用，产生比单独使用氯更大的各种水生病原体的失活效果。本研究将利用化学和微生物学工具的组合来量化在FAC光解增强的常规氯化过程中耐氯病毒、细菌和原生动物病原体的失活。这项工作的主要目的将是评估利用阳光的光化学增强氯化过程。然而，由于单色和多色紫外光源在饮用水处理中的应用频率越来越高，研究也将集中在其潜在的应用上。项目团队将开发并优化实验和分析程序，以量化光化学强化氯化过程中病原体的失活，首先利用水传播病原体枯草芽孢杆菌孢子和MS2噬菌体的两种常见替代品，然后利用耐氯人类病原体M. avium、柯萨奇病毒B5 （CVB5）和细小疟原虫。随后，这些程序将用于检查pH值、水温、碱度和基质氧化剂需求等关键参数对每种病原体在模拟阳光、自然阳光和缓冲实验室试剂水系统中各种人工紫外线光源下的灭活效率的影响，以及从普吉特海湾地区市政供水设施获得的真实水基质。将特别强调病原体灭活的动力学模型的发展，考虑到测量的水质参数和光谱辐照度数据。最后，将量化光化学强化氯化作用（如三卤甲烷、卤乙酸、ClO3-、ClO4-和BrO3-）过程中可能产生的有机和无机dbp的形成势。除了建立在光化学强化氯化过程中模拟抗氯病原体灭活的理论框架外，该项目还将提供适用于全面水处理（包括可变照射波长、强度、温度、pH和碱度）的各种条件下的M. avium、CVB5和C. parvum灭活的广泛数据集。这项研究可以支持光化学增加常规饮用水氯化工艺的规模，以最小的设备和工艺改造。这种方法的应用可能比现有的氯基消毒方法的替代品有实质性的好处。首先，绝大多数水处理设施都使用氯化。第二，与利用臭氧或人工紫外线的工艺相比，利用太阳辐射特别是作为光源可以节省大量的成本和能源。此外，如果一个设施已经有了紫外线处理，那么这个过程可以很容易地适应于光化学强化氯化，只需在紫外线反应器的上游添加FAC。此外，在发达国家和发展中国家的使用点应用过程中，由于预期成本低且易于实施，在确保对氯抗性病原体进行消毒方面，阳光强化氯化可能特别有用。

1236303DoddFree available chlorine (FAC) remains the most widely used disinfectant in drinking water practice worldwide. It is cheap, easily utilized as a disinfectant, portable, and in general highly effective for achieving the inactivation of a wide variety of waterborne microbial pathogens. However, it is known to be relatively ineffective as a primary disinfectant of such important pathogenic agents as Cryptosporidium parvum, Mycobacterium avium, and Giardia lamblia, This has led to widespread adoption of more effective, but often substantially more capital-, equipment-, and energy-intensive alternative disinfectants such as UV light and ozone. Recent findings suggest that inactivation of chlorine-recalcitrant microbial pathogens may actually be achievable at considerably lower expense by utilizing sunlight or monochromatic UV light to photolyze FAC to such highly-reactive oxidant species as hydroxyl radical, atomic oxygen, and ozone during conventional chlorination. In such an approach, FAC and photochemically-generated oxidants may act in tandem to yield substantially greater inactivation of various waterborne pathogens than would be achievable using chlorine alone. This investigation will utilize a combination of chemical and microbiological tools to quantify inactivation of chlorine-resistant viral, bacterial, and protozoan pathogens during conventional chlorination processes enhanced by FAC photolysis. The primary objective of this work will be to evaluate the use of sunlight for photochemical enhancement of chlorination processes. However, the investigation will also focus on potential applications of monochromatic and polychromatic UV light sources, on account of their growing frequency of application in drinking water treatment. The project team will develop and optimize experimental and analytical procedures for quantifying pathogen inactivation during photochemically-enhanced chlorination by first utilizing two common surrogates for waterborne pathogens B. subtilis spores and MS2 bacteriophage, followed by the chlorine-resistant human pathogens M. avium, Coxsackievirus B5 (CVB5), and C. parvum. These procedures will subsequently be utilized to examine the influence of such critical parameters as pH, water temperature, alkalinity, and matrix oxidant demand on inactivation efficiency for each pathogen under simulated sunlight, natural sunlight, and various artificial UV light sources in buffered laboratory reagent water systems, as well as in real water matrixes acquired from municipal water utilities in the Puget Sound region. Particular emphasis will be placed on development of kinetic models for pathogen inactivation that take into account measured water quality parameters and spectral irradiance data. Finally, formation potentials of organic and inorganic DBPs likely to be generated during application of photochemically-enhanced chlorination (e.g., trihalomethanes, haloacetic acids, ClO3-, ClO4-, and BrO3-) will be quantified under a variety of scenarios relevant to full-scale application. In addition to establishing a theoretical framework for modeling chlorine-resistant pathogen inactivation during photochemically-enhanced chlorination, this project will provide an extensive dataset for M. avium, CVB5, and C. parvum inactivation under a wide variety of conditions applicable to full-scale water treatment (including variable irradiation wavelength, intensity, temperature, pH, and alkalinity). This research could support the photochemical augmentation of conventional drinking water chlorination processes at full-scale, with minimal equipment and process retrofit. Application of such an approach could have substantial benefits over existing alternatives to chlorine-based disinfection processes. First, chlorination is used in the vast majority of water treatment facilities. Second, utilization of solar radiation in particular as a light source could net significant cost and energy savings in comparison to processes utilizing ozone or artificial UV light. In addition, if a UV process is already in place at a facility, that process could quite easily be adapted for photochemically-enhanced chlorination simply by dosing FAC upstream of the UV reactor(s). Furthermore, sunlight-enhanced chlorination could prove exceptionally useful for ensuring disinfection of chlorine-resistant pathogens during point-of-use applications in developed and developing societies, on account of its expected low costs and ease of implementation.