Coal-tar was commonly used as an internal lining for corrosion protection of water pipes from the 19th century up to the present. It is reported that these coatings can lead to elevated concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in the distributed drinking water. The aim of the project was to investigate the processes and mechanisms responsible for the occurrence of these substances in drinking water distribution systems. The results presented in this project showed that the occurrence of PAHs in a distribution system was linked to the presence of the disinfectants chlorine and chlorine dioxide. This dependence could be shown in the laboratory, in a pilot-scale pipe rig as well as in field investigations in a real distribution system. Generally, hostile environmental conditions for microbiological activity such as stagnation periods and anaerobic conditions could be identified as the most important factors to favour the occurrence of PAHs in the drinking water. It was clearly shown that disturbances in the hydraulic regime such as water hammers, operation of valves and rapid increases in flow velocity can result in enhanced PAH concentrations. Immediately after stagnation periods PAH concentrations increased to levels which exceeded the prescribed concentrations of the EC-guideline of 200 ng/l. In laboratory experiments it was demonstrated that the coal-tar is a substrate for the growth of biofilms. Batch experiments and reactor experiments showed that the removal of biofilm resulted in a higher leaching rate of the PAHs into the water. Experiments concerning the potential for the formation of chlorinated PAHs as disinfection by-products from the PAHs prevalent in water distributed through coal-tar lined pipes showed that their occurrence is very unlikely under conditions prevalent in water distribution systems. A theory is presented which indicates that particles adhering to the pipe walls which can be sometimes embedded in the biofilm matrix represent a major factor in the process of the mobilisation of PAHs. The destabilisation of the biofilm matrix by hostile environmental conditions (disinfectants, aerobic conditions, oxygen limitation during stagnation periods) or enhanced shear forces on the biofilm, results in the release of particles highly contaminated with PAHs.

Premise plumbing can contain copper and lead bearing fixtures, and although copper is considered primarily an aesthetic issue, the neurotoxic effects of lead present a significant public health concern. Utilities approach corrosion control in low alkalinity water by increasing the pH (>9) or adding a phosphate inhibitor at neutral pH. Phosphate inhibitors, pH and chlorine are known to affect lead and copper release through their direct action as corrosion inhibitors or oxidizing agents or through an indirect action via microbial growth. Biofilms are often an implied cause of premise plumbing corrosion, although little is known about their community structure or ability to store metals. The central hypothesis of this thesis is that biofilm contributes to lead and copper release in premise plumbing. This thesis addresses a unique gap in corrosion literature by integrating traditional corrosion chemistry methods with microbiological and molecular biology techniques. The experiments used three distinct approaches: (i). electrochemical cell experiments to determine the key factors in decreasing lead and copper corrosion in galvanically coupled systems while maintaining microbial control (ii). galvanic macrocells using premise plumbing components to examine the unintended consequences of adding a phosphate based corrosion inhibitor and (iii). an annular reactor study to examine the impacts of two commonly applied corrosion control strategies. In the electrochemical cell experiments, the pH 9.2 with zinc orthophosphate and chlorine treatment achieved both goals: decreased lead and copper release and limited microbial growth. In galvanic macrocells experiments with premise plumbing components, zinc orthophosphate addition was shown to be positively correlated with increased bulk water bacteria, biofilm growth and biofilm community structure as measured by DGGE. Biofilm was also observed to sorb 3-29% of lead and 3-16% of copper from the bulk water. The comparison of the two corrosion control strategies showed that the majority of lead released was in the particulate form, and the results further alluded to the potentially significant role lead particles play in biofilm formation.

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