Two-phase kinetics of biofilm removal during CIP. Respective roles of mechanical and chemical effects on the detachment of single cells vs cell clusters from a Pseudomonas fluorescens biofilm

Abstract

The objective of this study was to investigate the roles of mechanical and chemical actions on the detachment kinetics during CIP of biofilms of Pseudomonas fluorescens at a pilot-plant scale.Biofilms were grown 48 h at 20 °C in diluted milk. Shear stress conditions ranged from 0 (static) to 20 Pa and NaOH concentrations from 0.1 to 0.5% w/w. A simple two-phase model was applied to model the removal kinetics and compare detachment parameters.A quick removal of the biofilm during the first phase (4–5 log decrease in three minutes) was followed by a second phase of slow removal of the cells and small aggregates still present at the surface (0–2 log decrease). Hydrodynamics was responsible for removal of both biofilm and single cells while chemicals mainly disrupted biofilm clusters during the first phase. No complete biofilm removal was observed, suggesting a significant role of the interaction forces between bacteria and substrata in the CIP efficiency.