Disinfection by-product formation from biofilm chlorination in drinking water pipes

Biofilms in drinking water distribution networks (DWDNs) are recognized as potential pathogen reservoirs. Recent experiments have found that biofilm can also act as precursors for the formation of disinfection by-products (DBPs). This project aimed to better understand the impact of the presence of biofilms and improve prediction of DBPs in DWDNs. To study the microbial significance of biofilms in water pipes, bacterial communities in biofilm and bulk water were identified in a DWDN in a tropical climate country. Drinking water and biofilms were characterised by physico-chemical parameters. Relationships between biotic, physico-chemical parameters and engineered factors (i.e., pipe age, material and diameter; and water age) were explored by the application of statistical tests.
Additionally, improvement of DBP prediction in DWDNs was approached by modelling the role of biofilms as DBP precursors. Two models for predicting DBP formation potentials were developed from chlorination of cells and extracellular polymeric substances. The first model corresponded to stagnant conditions and a second more complex model was produced for transitional and turbulent flow. The models were implemented in the software COMSOL Multiphysics 5.2a and sensitivity analysis was carried out to screen the parameters influence on the response variables.
Field-work assessment allowed determining that biofilms are richer habitats than bulk water. Pipe age, pipe material, water age, free chlorine, pH and temperature can be key to the composition of bacterial communities. Model simulations suggested that the important DBP exposure is related to dichloroacetronitrile, stagnant bulk, and slow flow. The microbial and chemical significance of biofilms is important in the context of climate change and developing countries because water managers can face multiple challenges under these conditions. Alterations of raw water properties, increasing occurrence of extreme weather events and poor capacity to mitigate such events may rise the chemical and microbiological risk associated to biofilms in DWDNs in tropical countries.