Lead in Drinking Water: Reducing/Replacing Phosphate Dosing

饮用水中的铅(铅)已被证实是对公众健康的威胁，它仍然具有破坏性的后果，例如，美国弗林特当局的一系列错误导致当地人口大规模中毒。目前，自来水供应商有法律义务确保饮用水中的铅含量不超过一定浓度。合规性通常是通过pH控制和磷酸盐投加的组合来实现的，其目的是产生高度不溶的铅磷酸盐的表面膜，以限制溶解的铅的量(即铅的溶解性)。然而，水样表明，这种化学处理远远不是完美的，有时会超过法定的溶解铅限制。此外，越来越多的人担心，目前的磷酸盐处理制度很快将在经济上变得不可行，将需要替代解决方案；现有的磷酸盐剂量水平只是基于经验知识，很少或根本没有开展工作来探索变化的好处/坏处。基于以上原因，PHD项目的目标是检验以下假设：机械地理解DW管道中铅垢的演化/铅溶解路线将使减少/替换磷酸盐投加量的决策基于知识。与这一领域中进行的其他工作形成鲜明对比的是，这项工作不会关注退役的铅水管，这些管道有着复杂和模棱两可的历史，这固有地削弱了它们获得机械洞察的价值。相反，最初的工作将集中于阐明参考铅/干湿体系的比例/铅溶解度的时间演变，即在没有/存在磷酸盐剂量(PHOS)的情况下，将铅样品浸入明确的干湿化学中。这种方法将促进机械理解所需的透明度，包括评估两种潜在的铅溶解途径的相对重要性，即从铅盐/氧化物中释放铅与金属Pb的局部腐蚀。为了便于研究，制定了一系列可测量的研究目标，即：(I)实施适合于实验室研究铅水管中铅溶解/垢演变的实验装置/程序。(Ii)在参考的铅/DW磷酸盐体系中识别和量化铅溶解的途径。(Iii)描述在铅/DW磷酸体系中形成的垢的结构和化学。(Iv)量化减少磷酸盐投加量对铅溶解/结垢演变的影响。(V)阐明不同DW化学成分对铅溶解/结垢演变的影响。(Vi)利用实验数据开发基于知识的磷酸盐投加指南。(Vii)研究磷酸盐投加的可能替代方法。学生将使用先进的电子显微镜、光谱和衍射技术，将电化学测量/溶液分析与结垢特征相结合，跟踪铅溶解作为结垢演变的函数。预计这项计划将改变我们对饮用水中表面结垢和铅之间关系的理解，并为减少/取代磷酸盐投加量提供基础知识。因此，它将有助于EPSRC的以下优先事项：物理和数学科学的强国，工程和技术的前沿，以及转变卫生和医疗保健。

Lead (Pb) in drinking water is a proven threat to public health, which continues to have devastating consequences, e.g., a series of errors by authorities in Flint (USA) resulted in mass poisoning of the local population. Currently, water suppliers are legally obliged to ensure that the level of Pb in drinking water (DW) does not exceed a certain concentration. Compliance is typically pursued through a combination of pH control and phosphate dosing, which is intended to produce a surface film of a highly insoluble Pb phosphate salt that restricts the amount of dissolved Pb (i.e., plumbosolvency). Water sampling, however, indicates that this chemical treatment is far from perfect, and that the legal limit of dissolved Pb is sometimes exceeded. Moreover, there are increasing concerns that the current phosphate treatment regime will soon become economically unviable, and alternative solutions will be required; existing phosphate dosing levels are simply based on empirical knowledge, with little/no work undertaken to explore benefit/detriment of changes. Motivated by the above, the goal of the PhD project is to test the following hypothesis:Mechanistic understanding of Pb scale evolution/plumbosolvency routes in DW pipes will enable knowledge-based decisions on reducing/replacing phosphate dosing.In sharp contrast to other work undertaken in this arena, work will not be concerned with ex-service Pb-water pipes, which have complex and ambiguous histories that inherently undermine their value for gaining mechanistic insight. Instead, effort will focus initially on elucidating the temporal evolution of scale/plumbosolvency for a reference Pb/DW system, i.e., a Pb sample immersed in a well-defined DW chemistry, in the absence/presence of phosphate dosing (Phos). Such an approach will facilitate the transparency required for mechanistic understanding, including evaluating the relative importance of two potential plumbosolvency routes, i.e., Release of Pb from Pb salts/oxides versus Local corrosion of metallic Pb.To facilitate research delivery, a series of measurable research objectives have been devised, i.e.,(i) Implement experimental setups/procedures suitable for laboratory studies of plumbosolvency/scale evolution in Pb-water pipes.(ii) Identify and quantify routes for plumbosolvency in reference Pb/DW Phos system.(iii) Characterise structure and chemistry of scale formed in Pb/DW Phos system. (iv) Quantify impact of reducing phosphate dosing on plumbosolvency/scale evolution.(v) Elucidate impact of varying DW chemistry on plumbosolvency/scale evolution.(vi) Use experimental data to develop knowledge-based guidelines for phosphate dosing.(vii) Investigate possible alternatives to phosphate dosing.The student will combine electrochemical measurements/solution analysis with scale characteristaion, using advanced electron microscopy, spectroscopy and diffraction techniques, to follow plumbosolvency as a function of scale evolution. It is anticipated that this program will initiate a step-change in our understanding of the relationship between surface scale and Pb in drinking water and provide underpinning knowledge for reduction/replacement of phosphate dosing. Consequently, it will contribute to the following EPSRC priorities: the physical and mathematical sciences powerhouse, frontiers in engineering and technology, and transforming health and health care.