Assessing biological stability of drinking water produced by reverse osmosis and remineralisation: Method development and application

The aim of this thesis was to compare reverse osmosis and remineralisation with conventional treatment in terms of the Bacterial Growth Potential (BGP) of drinking water. However, existing BGP methods were unsuitable as the detection level was too high to measure ultra-low nutrient water produced by RO. Hence, the focus of this thesis was to: (i) further develop the method to reliably measure the BGP of RO permeate, (ii) apply the improved BGP method to compare RO and conventional treatment. Several improvements were made to the BGP method, resulting in >2.5-fold reduction in its detection limit, due to using an ultra-pure blank prepared from laboratory-remineralised RO permeate. Applying the improved method showed that the BGP of drinking water was reduced by >75% after RO compared with conventional treatment as >99% nutrient removal (carbon and phosphate) was achieved with RO. Moreover, remineralisation adversely affected RO permeate quality, and measures are recommended to mitigate the impact of post-treatment on BGP. The improved BGP method can be used to reliably monitor BGP of ultra-low nutrient water. This development opens up new avenues of research towards improved analytical techniques to identify compounds utilised by bacteria for growth and how to remove these during treatment as well as understanding the effect of ultra-low nutrient water on bacterial growth and ecology in distribution systems.