Ecological insights into assembly processes and network structures of bacterial biofilms in full-scale biologically active carbon filters under ozone implementation

To address the adverse effects of harmful algal blooms, there are increased demands over the implementation of ozone coupled with biologically active carbon (BAC) filters in the drinking water treatment plants. Although the microbial biofilms are vital elements to support the proper performance of BAC filters, except for taxonomic affiliations, little is known about the assembly mechanisms of microbial communities in the full-scale BAC filters. This study aimed to examine how the assembly processes and their associated factors (e.g., influent characteristics, biological interactions) drive the temporal dynamics of bacterial communities in full-scale BAC filters, which underwent ozone implementation (five consecutive seasons from 2017 to 2018). The results revealed that along with the increase of bacterial taxonomic richness and evenness, stochastic processes became more crucial to determine the bacterial community assembly in the summer and autumn after ozone implementation (relative contribution: 61.23% and 83.75%, respectively). Moreover, their corresponding networks possessed simple network structures with lower modularity than other seasons, which implied lesser biological interactions among bacterial populations. The correlation between taxonomic and predicted functional diversities using functional redundancy index indicated that relatively high levels of bacterial functional redundancy (>0.83) were generally present in BAC filters. However, compared to other seasons, significantly higher degrees of functional redundancy existed in the summer and autumn after ozone implementation (0.85 ± 0.01 and 0.86 ± 0.01, respectively). Overall, this work improves our understanding of the microbial ecology of full-scale BAC filters by providing a conceptual framework that characterizes bacterial biofilm assembly processes relevant to performance optimization of full-scale BAC filters.