A Practical Bacterial Biodosimetry Procedure to Assess Performance of Lab-Scale Flow-through Ultraviolet Water Disinfection Reactors

Biodosimetry can be used to estimate the fluence of a reactor by determining its ability to inactivate a challenge organism. Especially for small-scale flow-through reactors, inconsistent procedures are reported for bacterial cells. This study aims to develop a standardized, simple procedure for bacterial biodosimetry in flow-through UV systems with relevant biofilm-forming bacteria, to evaluate biofouling control by UV. In particular, the challenge organism, the type of experimental setup, and the execution of single steps during biodosimetry with bacterial cells can cause largely deviating results. Since previous work was restricted to model organisms, which are not relevant for biofouling, we critically re-evaluated all reported steps for the biofilm forming Aquabacterium citratiphilum and identified three main factors for biodosimetry reproducibility in flow-through systems: Protractions of cells from controls without UV can heavily impact inactivation efficacy but can be reduced by ordering samples by decreasing fluence. Further, to avoid photorepair, samples must be processed under red light only. Lastly, biofilm forming bacteria can strongly adsorb on plastic labware, which requires counter measures in the form of special labware and the addition of surfactants. Overall, the developed protocol provides a biodosimetry standardization for bacterial cells of flow-through systems, facilitating reproducibility and transferability of results between studies that use bacterial cells as a challenge organism.