Identifying critical operational control points and strategies to minimize microbial risk during drinking water treatment

原生动物病原体仍然是与提供安全饮用水有关的重大公共卫生威胁。由于极端天气事件的频率和强度增加，气候变化预计将加剧这些风险。在北美，大多数依赖地表水的饮用水公用事业利用化学辅助过滤(CAF)作为关键处理过程，这是原生动物进入经过处理的饮用水供应所必需的屏障。对于经过处理的水，传统的监测策略在确保去除原生动物方面是无效的，因为1)原生动物计数的方法不充分，2)CAF去除原生动物的可靠替代品不可用。为了保护公众健康不受水传播疾病的影响，传统的监管方法要求特定的设备“运转良好”。最近，世界卫生组织饮用水质量指南(GDWQ)建议水安全计划(WSP)作为一种显著不同的、更好的系统特定方法来管理饮用水中的病原体风险。在这里，关键控制点(CCP)代表可以应用控制的点、步骤或程序，因此，水安全危害可以被预防、消除或减少到可接受的水平。本文提出了一种基于CCP的方法来确保CAF去除原生动物。这项研究包括1)将定量微生物风险评估(QMRA)与CCP方法相结合，以最小化通过CAF的原生动物通道；2)开发用于快速识别和计数原生动物的图像分析工具。这项工作将有助于推进CAF在饮用水处理过程中的原生动物病原体风险管理。它将贡献新的知识，产生技术创新，并培养能够有效应用新兴科学工具进行风险评估的高素质人才，以制定改进的饮用水处理战略、技术和政策。这项研究的长期好处包括帮助降低与水有关的疾病的社会成本，并使创新的、针对水公用事业的WSP和适应战略能够应对土地干扰和气候变化。

Protozoan pathogens remain a significant public health threat associated with the provision of safe drinking water. Climate change is expected to exacerbate these risks due to increased frequency and intensity of extreme weather events. Most drinking water utilities reliant on surface water in North America utilize chemically-assisted filtration (CAF) as a key treatment process that is a required barrier to protozoan passage into treated drinking water supplies. Traditional monitoring strategies for treated water are ineffective at ensuring protozoan removal because 1) methods for the enumeration of protozoa are inadequate and 2) reliable surrogates for protozoan removal by CAF are not available. To protect public health from waterborne disease, traditional regulatory approaches have required specific equipment that is "well operated." Recently, the World Health Organization Guidelines for Drinking Water Quality (GDWQ) have recommended Water Safety Plans (WSPs) as a notably different, better, system-specific approach for managing pathogen risk in drinking water. Here, critical control points (CCPs) represent a point, step, or procedure at which control can be applied and, as a result, a water safety hazard can be prevented, eliminated, or reduced to an acceptable level. The development of a CCP-based approach for ensuring protozoan removal by CAF is proposed herein. The research includes the 1) integration of quantitative microbial risk assessment (QMRA) with the CCP-approach for minimizing protozoan passage through CAF and 2) development of an image analysis tool for rapid protozoan identification and enumeration. This work will help to advance protozoan pathogen risk management by CAF during drinking water treatment. It will contribute new knowledge, generate technological innovation, and train highly qualified personnel who can effectively apply emerging scientific tools for risk assessment to develop improved drinking water treatment strategies, technologies, and policies. The long-term benefits of this research include helping to reduce the societal costs of water-related illnesses and enabling innovative, water utility-specific WSPs and adaptation strategies in response to land disturbances and changing climate.******