Impact of Chloramination on the Development of Oligotrophic Biofilms

This study aimed to i) determine the effectiveness of monochloramine disinfection on biofilm control and ii) characterize the architecture and community development of laboratory-grown oligotrophic biofilms over a two-month period. Biofilm development and disinfection were realized in Center for Disease Control (CDC) reactor systems with PVC coupons as the substratum and groundwater as the seeding and growth nutrient. To compare biofilm development under disinfection against its natural development, two CDC reactors (treatment and control) were operated. In the treatment reactor, chloramination at 8.5 ± 0.2 mg Cl2/L as combined chlorine was applied after two weeks of biofilm growth till the end of week 10. Confocal laser scanning microscopy combined with quantitative analysis using COMSTAT program revealed that disinfection resulted in a reduction of average thickness and biomass volume by 83.6% and 81.8%, respectively, and an increase in compactness by 76.5%, suggesting the formation of a thin and compact biofilm with low biomass. In contrast, biofilm development in the control reactor led to an increase in average thickness and biomass volume by a factor of 5.2 and 47.1%, and a reduction in compactness by 75.5%. As the result, thicker and fluffier biofilm architecture was observed. Biofilm community structure change was revealed by cluster analysis and non-metric multidimensional scaling based on 16S rRNA gene-based microbial fingerprinting analysis. Samples from different reactors at the same time point had a high similarity before disinfection, but became dissimilar after disinfection. This suggested that disinfection could lead to the development of a biofilm community with a distinctive community structure. Overall findings suggest that disinfection could influence the growth of multi-species biofilms on PVC surface, shape the biofilm architecture, and select a microbial community thatcan survive, adapt, or proliferate under chloramination. These findings are important to better understand biofilm growth in chloraminated drinking water distribution systems