Field Investigation Of Discolouration Material Accumulation Rates In Live Drinking Water Distribution Systems PDF Download

Although compliance rates are improving, discoloured water is the main area of water quality related customer complaints within the UK water industry. To enable a move from reactive to proactive management research is required to generate better understanding of discolouration. Previous investigations into factors influencing discolouration have been mainly based on bench scale tests or live networks, however these methods have limitations which restrict the progression of aspirations towards further knowledge. It has been observed that higher levels of discolouration complaints are received during warmer months. A link between increased coliforms and temperature has likewise been observed. From such work it is possible to hypothesise a connection between microbial ecology, particularly biofilms, and discolouration with temperature an important influencing variable, but to date such associations have not been proven. Likewise the impact of shear stress on discolouration potential is largely difficult to quantify. Questions remain over the influence of conditioning shear stress; whether it is the average or peak flow that influences discolouration and the pattern of mobilisation of particles. In order to investigate these hypotheses and address limitations of past studies a novel, full size temperature controlled pipe facility was developed offering a compromise between the dynamics of a live network and control of potentially influential factors. Coupons, designed to minimise distortion of boundary layer flow, were positioned along each loop allowing the analysis of material at the pipe surface. Results are reported from four experiments comprising of a 28 day accumulation phase, followed by sequential flushing to examine the impact of conditioning temperature and shear stress on discolouration risk as characterised by bulk water samples (turbidity, iron and manganese) and biofilm pipe wall measurements. Overall the big contribution of this thesis was to for the first time prove a link between discolouration and microbiology. As part of the implications of this relationship big advancements were made through the confirmation that higher temperatures increase discolouration risk. Discolouration was likewise seen to decrease with increased shear with the peak in flow being more influential than the average flow at reducing discolouration risk. Temperature was observed to be the controlling factor over shear stress in this relationship.