Examining the growth and mobilization behavior of early-stage biofilms in a controlled, pilot scale PVC drinking water system laboratory

Abstract

The aim of this paper was to examine the growth and mobilization behavior of early-stage biofilms in a pilot scale, controlled PVC drinking water system. An alternative method for biofilm growth used a concentrated solution of microorganisms sourced in tap water to inoculate the pipe system and allowed biofilms to be formed over a 28-day period. Biofilm development was also assisted with nutrient addition and disinfection depletion from the experimental system water. The pipe loop was then flushed to mobilize these biofilms. The growth and mobilization of the biofilms were assessed with molecular and fluorescence microscopy analysis of bulk water samples and removable pipe wall samples. Results showed that: (1) biofilms followed a rapid growth period on the pipe wall between 0 and 14 days, and 21 and 28 days; (2) biofilm growth was apparently halted between 14 and 21 days, likely because of a shift in bacterial community composition; (3) biofilms were observed to preferentially accumulate at the invert pipe position along the full longitudinal direction of the pipe but rapidly decreased for the springline and obvert circumferential positions of the pipe; (4) a flushing flow of 6.5 L s⁻¹ (1.2 Pa) was not able to fully remove the biofilms from the pipe wall; (5) biofilms were observed to form in clusters on the pipe wall which remained fully attached to the pipe wall even after flushing. Biofilms investigated here were likely impacted by the alternative growth method, but their physical structure still resembles biofilms from operational DWDSs. The research findings add to the emerging knowledge concerning the growth and mobilization of biofilms in drinking water systems. In addition, the alternative method to investigate biofilms is highly reproducible and can facilitate future studies in the field.