Microbial Stratification and DOM Removal in Drinking Water Biofilters Implications for Enhanced Performance
Biofiltration is a low-cost, low-energy technology that employs a biologically activated bed of porous medium to reduce the biodegradable fraction of the dissolved organic matter (DOM) pool in source water, resulting in the production of drinking water. Microbial communities at different bed depths within the biofilter play crucial roles in the degradation and removal of DOC, ultimately impacting its performance. However, the intricate relationships between the compositions of microbial communities inhabiting different biofilters and their utilisation of various DOC fractions remain poorly understood. To address this knowledge gap, we conducted an experimental study where microbial communities from the upper and lower sections of a laboratory-scale biofilter were recovered. These communities were then individually incubated for 10 days using the same source water as the biofilter influent. Our study revealed that the bottom microbial community exhibited lower diversity yet a co-occurrence network with a higher degree of interconnections among its members compared to the top microbial community. Moreover, we established a direct correlation between the compositional and network structure of the microbial communities and their ability to utilise various DOM fractions within a DOM pool. Interestingly, despite the bottom microbial community starting with only 20% of the total cell abundance compared to the top community, the bottom microbial community utilised and hence removed approximately 60% more total DOC from the DOM pool than the top community. While both communities rapidly utilised labile carbon fractions, such as low-molecular-weight neutrals, the utilisation of more refractory carbon fractions, like high-molecular-weight humic substances with a molecularity of more than ca. 1451 g/mol, was exclusive to the bottom microbial community. By employing techniques that capture microbial diversity (e.g., flow cytometry and 16S rRNA amplicon sequencing) and consider the complexities of DOM (e.g., LC-OCD), our study provides novel insights into how microbial community structure could influence the microbial-mediated processes of engineering significance in drinking water production. Finally, our findings implied the opportunity to improve biofilter performances via engineering interventions that shape the compositions of biofilter microbial communities and enhance their utilisation and removal of DOM, especially the refractory DOM fractions.