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 dissolved organic carbon (DOC), ultimately impacting its performance. However, the relationships between the composition of microbial communities inhabiting different biofilter depths 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 (i.e., top 10 cm) and lower (i.e., bottom 10 cm) sections of a 30-cm long 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 had 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 composition and network structure of the microbial communities and their ability to utilise various DOM compounds within a DOM pool. Interestingly, although the bottom microbial community had only 20 % of the total cell abundance compared to the top community at the beginning of the incubation, it 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 an average molecular weight of more than ca. 1451 g/mol, was exclusive to the bottom microbial community. By employing techniques that capture microbial diversity (i.e., flow cytometry and 16S rRNA amplicon sequencing) and considering the complexities of DOM (i.e., LCOCD), 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 could offer 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, most notably the more classically humified and refractory DOM compound groups.

The present study explored the incorporation of health-related organisms within drinking water biofilms and bulk water quality using benchtop-scale distribution systems. The annular reactors simulated the dead-end pipes of distribution systems with low shear stress but maintained a chlorine residual and formed young biofilms on plastic surfaces. Spiked coliforms and Escherichia coli were introduced to the annular reactors after 1 month of growth. Although initially detected in the spike, the coliforms were inactivated in the bulk water phase, likely due to environmental stresses, such as nutrient starvation and residual chlorine. Also, coliform incorporation within biofilm was only detected in a single coupon in the reactor 24 h post-spike (with 100% lake water), suggesting they were not incorporated or under the detection limit.

Background: Biofiltration offers a sustainable, low-energy solution for drinking water treatment but suffers from inconsistent performance due to complex microbial dynamics. Current studies lack insight into early biofilter microbial community assembly. Here we perform a high-resolution spatial and temporal investigation of biomass accumulation and community development within biological activated carbon (BAC) filters over the first 6 months of operation. Results: We found that initial biomass accumulation is not linear, instead characterised by periods of growth and decay. Mass balance identified an estimated + 6.54 × 10 ⁸ new cells daily during the growth phase (days 34–62), falling to a loss of 1.69 × 10 ⁹ by the decay phase (days 83–162). There was no significant increase in richness until the decay phase (ANOVA p values > 0.05 between days 34, 62 and 83). Significant stratification (ANOVA p values < 0.05) was observed with bed depth with 79% (± SD2.7%) of biomass found in the top 15 cm of the filter bed, the bottom section (90 cm) had 36.5-fold lower biomass. An abundant community of 20 primary colonisers made up to between 20 ± SD8% and 80 ± SD5% of the total community and persisted over time. This community increased in absolute number during the growth phase (140% increase) however remained stable after this. Conversely rare taxa were found to continue to increase into the decay phase (131% between days 62–162). Core community analysis and neutral modelling of the seeding influent water and the biofilter found that the abundant taxa stochastically assembled early from the water, while the rare taxa driving changes in diversity, were selected by deterministic factors within the filter bed with 38% advantaged by the filter environment, compared to only 20% of the persistent abundant community. Conclusion: This study demonstrates that biofilter microbial communities undergo dynamic changes, with abundant early colonizers persisting steadily while rare taxa drive fluctuations in biomass through phases of growth and decay. Understanding these microbial dynamics and ecological interactions can inform engineering strategies to optimize biofilter performance, enhancing water treatment efficiency by targeting key microbial groups throughout filter maturation.

The potential of DWDS pipewall biofilms to shelter and propagate opportunistic pathogens is currently poorly understood. Here, we use an annular biofilm reactor approach to quantify the fate of the opportunistic pathogen Pseudomonas aeruginosa when introduced to a simulated DWDS environment. We found that P. aeruginosa was capable of swift attachment to surfaces and able to persist for up to 14 days under shear stress conditions. Further, we demonstrate that P. aeruginosa is capable of detachment/reattachment and mobilisation through the bulk water, potentially acting as a source of inoculum to drinking water.

The accumulation, growth, and re-mobilization of pathogens on the pipe walls in drinking water distribution systems are processes that affect the risk of exposure at the tap. We present a model that uses the Buckingham Pi theory to embody the physics of Pseudomonas aeruginosa accumulation and move within the system. We apply it to model experimental data from a biofilm annular reactor operated in conditions that are commensurate with the flow in DWDS. By calibrating the model for this benchtop system, we intend to identify the most important physical parameters for use in a simpler, more prudent model, for application in large-scale DWDS.