Biofouling is a major concern for numerous reverse osmosis membrane systems. UV pretreatment of the feed stream showed promising results but is still not an established technology as it does not maintain a residual effect. By conducting accelerated biofouling experiments in this study, it was investigated whether low fluence UV in situ treatment of the feed using UVC light-emitting diodes (UVC-LEDs) has a lasting effect on the biofilm. The application of UVC-LEDs for biofouling control is a novel hybrid technology that has not been investigated, yet. It could be shown that a low fluence of 2 mJ∙cm−2 delays biofilm formation by more than 15% in lab-scale experiments. In addition, biofilms at the same feed channel pressure drop exhibited a more than 40% reduced hydraulic resistance. The delay is probably linked to the inactivation of cells in the feed stream, modified adsorption properties or an induced cell cycle arrest. The altered hydraulic resistance might be caused by a change in the microbial community, as well as reduced adenosine triphosphate levels per cells, possibly impacting quorum sensing and extracellular polymeric substances production. Due to the observed biofilm attributes, low fluence UV-LED in situ treatment of the feed stream seems to be a promising technology for biofouling control.

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 biofilmforming 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.

No abstract

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 in order 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 organism, which are not relevant for biofouling, we critically reevaluated 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 negative controls can heavily impact inactivation efficacy, but can be reduced by ordering samples by decreasing fluence. Further, to avoid photo repair, samples must be processed under red light only. Lastly, biofilm forming bacteria can strongly absorb on plastic labware, which requires counter measures in 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 challenge organism.

No abstract