To Chlorinate or Not to Chlorinate

世界上大多数国家都保留有消毒剂残留，以控制饮用水分配系统(DWDS)内的浮游微生物污染和/或再生长。相反，一些欧洲国家禁止这种做法，因为残留物会产生消毒副产品，这些副产品是具有致癌作用的受管制毒素。关键的是，消毒剂残留物对生物膜的影响尚不清楚，包括它们在为病原体创造有利环境方面的作用。生物膜生长在所有表面上；它们是嵌入细胞外聚合物中的微生物细胞的基质。由于生物膜在很大程度上主导了DWDS的有机成分，因此有必要对DWDS消毒和生物膜相互作用的过程和影响进行明确的调查，以便能够理解和平衡消毒残留策略的所有风险和好处。这种平衡对于安全饮用水的持续供应是至关重要的，但只需最少的能源和化学物质的使用。中心的挑衅性主张是，消毒剂残留物促进具有抗性的生物膜，作为病原体的有利栖息地，允许病原体繁殖并零星地动员到水体中，然后对公众健康构成威胁。这个项目将首次研究和模拟消毒剂残留策略对生物膜的影响，包括病原体的庇护、增殖和动员，以填补DWDS知识中的这一重要空白。由于这一基础设施的老化性质，我们的DWDS中的病原体的潜在来源正在增加，例如，通过减压事件期间的泄漏入口。进入的量很小，因此直接暴露的风险很小，但可能会将病原体播种到生物膜中，有可能扩散和随后释放。一个完整的、迭代的物理实验和建模连续体对于实现拟议研究的雄心壮志至关重要。我们将利用微生物学、国际上独有的中试规模实验设施、种群生物学和微生物风险评估模型的最新发展，了解饮用水配水系统的消毒残留物、生物膜、病原体和水力学之间的相互作用。这项研究将结合全球知名的数学建模、饮用水工程、定量微生物风险评估和分子微生物生态学方面的专业知识，以交付这一雄心勃勃的、具有变革性的项目。如果核心命题得到证实，那么英国和大多数发达国家目前的做法可能是通过使用消毒剂残留物来增加健康风险。这项研究产生的证据将是全面风险评估的核心。一个可能的结果是，通过检验这一假设，我们将证明在什么条件下生物膜的选择压力是不可接受的，这样做可以了解并优化不同处理水特性的消毒残留物类型和浓度。虽然研究的重点是消毒剂残留物和病原体的影响，但这项研究也将使人们更广泛地了解饮用水分配系统中的生物膜行为、生物膜与水质之间的相互作用和影响，并与其他领域相关。这项研究的影响将是通过充分了解急性饮用水病原体(目前未知)和慢性消毒剂副产品(已知和不断增加)之间的权衡，在保护公众健康的同时最大限度地减少化学和能源消耗。由于水质与公众健康之间的内在联系，最终的受益者将是公众、社会和经济。

The majority of countries around the world maintain a disinfectant residual to control planktonic microbial contamination and/or regrowth within Drinking Water Distribution Systems (DWDS). Conversely, some European countries prohibit this practice because the residuals react to create disinfection by-products, which are regulated toxins with carcinogenic effects. Critically, the impact of disinfectant residuals on biofilms is unknown, including their role in creating a preferential environment for pathogens. Biofilms grow on all surfaces; they are a matrix of microbial cells embedded in extracellular polymeric substances. With biofilms massively dominating the organic content of DWDS, there is a need for a definitive investigation of the processes and impacts underlying DWDS disinfection and biofilm interactions such that all the risks and benefits of disinfection residual strategies can be understood and balanced. This balance is essential for the continued supply of safe drinking water, but with minimal use of energy and chemicals.The central provocative proposition is that disinfectant residuals promote a resistant biofilm that serves as a beneficial habitat for pathogens, allowing pathogens to proliferate and be sporadically mobilised into the water column where they then pose a risk to public health. This project will, for the first time, study and model the impact of disinfectant residual strategies on biofilms including pathogen sheltering, proliferation, and mobilisation to fill this important gap in DWDS knowledge.The potential sources of pathogens in our DWDS are increasing due to the ageing nature of this infrastructure, for example, via ingress at leaks during depressurisation events. Volumes of ingress and hence direct exposure risks are small but could seed pathogens into biofilm, with potential for proliferation and subsequent release. An integrated, iterative continuum of physical experiments and modelling is essential to deliver the ambition of the proposed research. We will make use of the latest developments in microbiology, internationally unique pilot scale experimental facilities, population biology and microbial risk assessment modelling to understand the interactions between the disinfection residuals, biofilms, pathogens and hydraulics of drinking water distribution systems. This research will combine globally renowned expertise in mathematical modelling, drinking water engineering, quantitative microbial risk assessment, and molecular microbial ecology to deliver this ambitious and transformative project.If the central proposition is proven, then current practice in the UK and the majority of the developed world could be increasing health risks through the use of disinfectant residuals. The evidence generated from this research will be central to comprehensive risk assessment. A likely outcome is that by testing the hypothesis, we will prove under what conditions the selective pressures on biofilms are unacceptable, and in so doing understand and enable optimisation of disinfection residuals types and concentrations for different treated water characteristics. Although focused on the impacts of disinfectant residuals and pathogens, the research will also generate wider knowledge of biofilm behaviour, interactions and impacts between biofilms and water quality within drinking water distribution systems in general and relevant to other domains.The impact of this research will be to deliver a step change in protecting public health whilst minimising chemical and energy use through well informed trade-offs between acute drinking water pathogen (currently unknown) and chronic disinfectant by-product (known and increasing) exposure. The ultimate beneficiaries will be the public, society and economy due to the intrinsic link between water quality and public health.