Proof-of-concept approach to assess the impact of thermal disinfection on biofilm structure in hot water networks

Temperature-based strategies are commonly applied to control microbial growth, but the impact of those pro-cedures on biofilm structure is usually not evaluated. This study investigates how thermal disinfection proced-ures affect pre-established Pseudomonas fluorescens biofilms, formed in a Center for Disease Control (CDC) biofilm reactor. It also assesses the biofilm regrowth potential over 24 h, under 125 and 225 rpm. Biofilms structure was compared at the mesoscale (thickness) and at the microscale (biovolume and surface coverage). Results showed that the impact of the thermal disinfection on the biofilm structure depends on the hydrodynamic conditions, which are also critical to the biofilm structural rearrangement upon regrowth. A thickness reduction of 80 % was found after the shock for biofilms formed under 125 rpm, however there was no significant biofilm sloughing off for the 225 rpm. Surface coverage was reduced by 65 % and 6 % after the thermal shock for 125 and 225 rpm, respectively. Furthermore, results seem to indicate that regardless the biofilm structural characteristics, bacteria recovered their culturability and viability to similar values to the ones before the thermal shock. This work provides an initial framework to develop more sustainable and effective thermal disinfection procedures in engineered water networks.