Lead in Drinking Water: Reducing/Replacing Phosphate Dosing

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.