Discolouration loose deposits in distribution systems: Composition, behaviour and practical aspects

Abstract

The main objective of the thesis is to contribute to a better understanding of the possible origins and development processes underlying tap water discolouration. With that purpose, qualitative and practical approaches were used for collecting loose deposits samples from distribution networks, i.e., methodologies that may be used together with daily routine procedures by the water companies to prevent and interpret loose deposits accumulation. To investigate the origins of loose deposits, samples were subjected to physical?chemical characterisation, not only for their typical components (Fe, VS), but also for some organic constituents (i.e., EPS). To study loose deposits behaviour, loose deposits observations were followed by stereoscope and microscopy visualizations, as well as turbidity decrease measurements. Studies on loose deposits build?up were assessed with pilot scale experiments, for better knowledge on the loose deposits formation processes taking place at drinking water distribution systems. The microbiological relevance of discolouration loose deposits was also evaluated, including the possible role of bacteria in loose deposits accumulation, in order to appraise the possible effects on water quality upon loose deposits resuspension. Thus, this thesis aims to improve knowledge on the “whys” and “hows” of discolouration events in drinking water distribution systems. More specifically, emphasis was given to understand how such light particulates may accumulate and resist to the shear stresses occurring in drinking water distribution systems, before loose deposits resuspend at one time and cause tap water discolouration.