Impacts of temperature and hydraulic regime on discolouration and biofilm fouling in drinking water distribution systems

Abstract

Discolouration is the greatest cause of customer dissatisfaction with drinking water quality, potentially masking other failures, including microbial issues, which can impact public health and well-being. The theorised association between biofilms (complex microbial communities) and discolouration within drinking water distribution systems (DWDS) was explored, whilst studying the impact and interactions of seasonal temperature variations and hydraulic regime. Transferability of findings to operational DWDS was ensured by using a temperature controlled, full-scale distribution experimental facility. This allowed isolation of the factors of interest, with integration of physical, chemical and microbial analyses. Greater discolouration and biofilm cell accumulation was observed under warmer (summer, 16°C) temperatures compared to cooler (winter, 8°C), evidence of microbiology being an important driver in DWDS discolouration behaviour. Temperature was generally more influential upon discolouration and biofilm cell volumes than the shear stress imposed by the hydraulic regimes, which included three steady state and two varied flow patterns. However, the trends were complex, indicating interactions between the two parameters in governing microbial accumulation and discolouration. These results are important in informing sustainable management of our ageing DWDS infrastructure to deliver safe high quality drinking water. By providing new evidence that discolouration is a biofilm/microbiologically-mediated process, we can better understand the importance of targeting interventions to hotter seasons, and manipulating hydraulic conditions (which we can control), to minimise the long-term impacts of impending changing climates on water quality.

Simulating long term discolouration behaviour in large diameter trunk mains

“…This supports the theory that material accumulation is a biologically mediated process as higher water temperature is associated with increased microbiological and therefore biofilm activity. 27,29 It would therefore be expected to observe more material accumulating during warmer periods, as also seen by Blokker and Schaap. 9 Higher material accumulation in the warmer seasons however could also be linked to the higher treated water organic and inorganic metal concentrations loadings, as shown in Fig.…”

“…23–25 Material accumulation, and hence discolouration risk, have been reported to be influenced by daily hydraulic conditions, 2,11,26 pipe material 15 and water temperature. 16,27 While some studies have showed temperature and microbial influence on discolouration risk, 16,27–29 the variation of accumulation processes and rates seasonally has not yet been rigorously demonstrated.…”

Emerging investigator series: optimisation of drinking water biofilm cell detachment and sample homogenisation methods for rapid quantification via flow cytometry

“…Hydraulics have been repeatedly documented to influence biofilm volume, EPS composition, cohesive strength, morphology, growth rates and community composition. [39][40][41][42][43][44][45] Biofilm-hydraulic trends do not converge in the literature, with some studies reporting increased density and adhesion/ cohesion with increased shear stress or velocity 41,45 and others observing the opposite, that adhesion/cohesion is reduced under greater ranges of velocity. 42,44 The range of impacts of hydraulics on biofilm characteristics is likely due to different operating conditions and sampling procedures.…”

Climate change and management of biofilms within drinking water distribution systems

“…Sometimes, flushing can be applied in conjunction with high concentrations of disinfectant (i.e., hyperchlorination) for more effective system cleaning, especially after pipes burst and are repaired (Chaves Simões and Simões, 2013;van Bel et al, 2019). These cleaning methods are known not to completely eliminate biofilm in the networks but remove weaker attached material that is commonly associated with the greatest risk to water quality, including discoloration (Douterelo et al, 2013;Fish, 2013). It is also known that the microorganisms remaining attached to the pipe wall can contribute to biofilm regrowth (Douterelo et al, 2014a).…”