Microbial biofilm communities on Reverse Osmosis membranes in whey water processing before and after cleaning

Abstract

The need for recovering valuable compounds and water from side streams has increased the use of Reverse Osmosis (RO) membrane filtration in the food industry. RO membranes, however, are highly susceptible to biofilm formation, which may decrease performance and increase industrial costs. In order to identify and characterize the biofilm forming communities, industrial RO membranes from whey water recovery lines in a dairy industry were investigated before and after Cleaning-In-Place (CIP) treatments. Phase contrast and Confocal Laser Scanning Microscopy (CLSM) were used to visualize the biofilms. The Heterotrophic Plate Count (HPC) and yeast population were enumerated, and 16S, 26S, and ITS rRNA sequencing was employed to identify the dominant isolates. A dense biofilm of the filamentous yeast species Saprochaete clavata and Magnusiomyces spicifer was observed together with budding yeasts and Gram-negative bacteria. The filamentous yeasts had long hyphae, which spatially dominated the biofilm on the retentate and permeate surface and they were not inactivated by the standard CIP treatment. Since neither plate counts nor DNA-based methods reflect the wide membrane coverage of the filamentous yeasts, their role in biofouling may easily be underestimated. We suggest that filamentous yeasts are included in further research on fouling of water treatment membranes in the dairy industry when investigating the effect of different CIP treatments or new RO membrane properties.