Influence of Wall Biofilm on Pathogen Transport in Water Distribution Systems. Modeling Estimates Derived from Synthetic Biofilm Experiments

Biofilm on pipe wall surfaces can modify the transport times and transient response of microbial contaminants that enter a potable water distribution system. The aim of this research is to develop an understanding of the key processes and forces that regulate dynamics of particles transport between wall biofilm and bulk water, and to derive an appropriate model alongside with the corresponding parameters describing these phenomena. To focus on the often-neglected influence of hydrodynamics on the transfer of microorganism from bulk to biofilm, a synthetic biofilm made of agarose gel is tested. The material is shown to retain mechanical integrity for high shear application and has proven to capture inert particles at a higher rate than blank surface in absence of biofilm. Accumulation on and release from the model-biofilm are experimentally studied and give evidence that the processes are influenced by hydrodynamic forces and particle size. The experimental findings were interpreted to derive rate coefficients for mathematical descriptions of the processes found for similar problems in the literature and for models derived from mathematical principals. Rate coefficients of simplistic accumulation and release models were found to be lower than reported in the literature for biofilm attachment and detachment. The mathematical descriptions accounting for the processes to depend on mass transfer and shear stress were able to depict the tendencies in the experimental results and provided the best goodness of fit. To apply the current derived model in a predictive risk assessment model of detachment of biofilm has to be included in the model.