The mobilisation of polycyclic aromatic hydrocarbons (PAHs) from the coal-tar lining of water pipes

Abstract

The use of coal-tar as an internal lining for corrosion protection of water pipes was a common procedure from the 19th century up to the mid-1970s. 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 achieved in that research project showed that the occurrence of PAHs in a drinking water distribution system was linked to the presence of chlorine and chlorine dioxide used for common disinfection practice. In laboratory experiments it could be shown that the coal-tar surface represents a substrate for the growth of biofilms which exhibits protective effects. Generally, hostile environmental conditions for microbiological activity of the biofilm such as disinfection, stagnation periods and anaerobic conditions could be identified as important factors which favour the occurrence of PAHs in drinking water. Immediately after stagnation periods an increase of PAH concentrations was observed. Moreover, 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 by the destabilisation of the biofilm matrix or high shear forces affecting the pipe walls resulting in the release of particles highly contaminated with PAHs which may be responsible for the contamination of the drinking water.