Modeling Biofilm Growth Rates in a Premise Plumbing Pipe without Disinfectant Residuals

Abstract

Premise plumbing systems without disinfectant residuals can develop thick biofilms, increasing health risks from biofilm-associated opportunistic pathogens. Yet existing models do not treat drinking water biofilms as true biofilms, with increasing thicknesses and substrate gradients within the biofilm, or consider the effects of substrates leaching from pipes into the biofilm. We developed a one-dimensional model of a nonchlorinated premise plumbing pipe to study factors affecting biofilm growth rates. Short stagnation times and pipes leaching biodegradable substrates favored biofilm growth over planktonic. Biofilm growth rates were predicted to be 70% higher when the stagnation period decreased from 12 to 6 h and 80% lower when the stagnation period increased from 12 to 48 h. Higher incoming concentrations of planktonic bacteria decreased biofilm growth rates, although only by 3.5% when the concentration of planktonic bacteria increased from 100 to 10,000 cells/mL. Smaller diameter pipes decreased overall planktonic growth due to greater availability of bulk nutrients to the biofilm. However, smaller diameter pipes also decreased biofilm growth due to the reduction in available nutrients. Overall, this research identified key factors promoting biofilm growth in unchlorinated premise plumbing systems, which could help develop more effective biofilm management strategies.