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

1236303无氯有效氯(FAC)仍然是全世界饮用水实践中使用最广泛的消毒剂。它价格便宜，易于用作消毒剂，便于携带，通常对各种水传播的微生物病原体实现灭活非常有效。然而，众所周知，作为一种主要消毒剂，它对微小隐孢子虫、禽分枝杆菌和蓝氏贾第鞭毛虫等重要病原体的主要消毒剂效果相对较差，这导致广泛采用更有效但往往更耗资、设备和能源密集型的替代消毒剂，如紫外线和臭氧。最近的发现表明，在传统的氯化过程中，通过利用阳光或单色紫外光将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灭活耐氯微生物病原体。在这种方法中，FAC和光化学产生的氧化剂可以协同作用，产生比单独使用氯更大的灭活各种水传播病原体的效果。这项研究将利用化学和微生物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灭活。这项工作的主要目标将是评估太阳光在光化学强化氯化过程中的使用。然而，由于单色和多色紫外光光源在饮用水处理中的应用频率越来越高，调查还将侧重于它们的潜在应用。该项目组将首先利用枯草杆菌芽胞和MS2噬菌体的两种常见替代品，然后是耐氯的人类病原体M.avium、柯萨奇病毒B5(CVB5)和微小杆菌，开发和优化实验和分析程序，以量化光化学增强氯化过程中病原体的灭活。这些程序随后将被用来检验诸如pH、水温、碱度和基质氧化剂需求等关键参数对每个病原体在模拟阳光、自然阳光和缓冲实验室试剂水系统中的各种人造紫外光光源下的灭活效率的影响，以及在从普吉特海湾地区的市政自来水公司获得的真实水基质中的影响。将特别重视发展病原体灭活动力学模型，其中考虑到所测量的水质参数和光谱辐照度数据。最后，在与全面应用相关的各种情况下，将量化在应用光化学增强氯化过程中可能产生的有机和无机DBPs(例如，三卤代甲烷、卤代乙酸、ClO_3~-、ClO_4~-和BrO_3~-)的形成潜力。除了建立光化学增强氯化过程中抗氯病原体灭活的理论框架外，该项目还将提供广泛的数据集，用于在适用于全规模水处理的各种条件(包括可变的照射波长、强度、温度、pH和碱度)下灭活禽类分支杆菌、CVB5和微小弧菌。这项研究可以支持常规饮用水氯化工艺的光化学强化，只需最少的设备和工艺改造。与现有的氯基消毒程序的替代品相比，应用这种方法可能会有很大的好处。首先，绝大多数水处理设施都使用氯化处理。其次，与使用臭氧或人造紫外光相比，利用太阳辐射特别是作为光源可以节省大量成本和能源。此外，如果设施中已经安装了紫外光工艺，只需在紫外光反应器上游投加FAC，该工艺就可以非常容易地用于光化学强化氯化(S)。此外，由于阳光强化氯化消毒预计成本较低且易于实施，因此在发达国家和发展中国家的使用点应用期间，可特别有助于确保对耐氯病原体进行消毒。

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.