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The general consensus is that the abundance of tap water bacteria is greatly influenced by water purification and distribution. Those bacteria that are released from biofilm in the distribution system are especially considered as the major potential risk for drinking water bio-safety. For the first time, this full-scale study has captured and identified the proportional contribution of the source water, treated water, and distribution system in shaping the tap water bacterial community based on their microbial community fingerprints using the Bayesian "SourceTracker" method. The bacterial community profiles and diversity analyses illustrated that the water purification process shaped the community of planktonic and suspended particle-associated bacteria in treated water. The bacterial communities associated with suspended particles, loose deposits, and biofilm were similar to each other, while the community of tap water planktonic bacteria varied across different locations in distribution system. The microbial source tracking results showed that there was not a detectable contribution of source water to bacterial community in the tap water and distribution system. The planktonic bacteria in the treated water was the major contributor to planktonic bacteria in the tap water (17.7-54.1%). The particle-associated bacterial community in the treated water seeded the bacterial community associated with loose deposits (24.9-32.7%) and biofilm (37.8-43.8%) in the distribution system. In return, the loose deposits and biofilm showed a significant influence on tap water planktonic and particle-associated bacteria, which were location dependent and influenced by hydraulic changes. This was revealed by the increased contribution of loose deposits to tap water planktonic bacteria (from 2.5% to 38.0%) and an increased contribution of biofilm to tap water particle-associated bacteria (from 5.9% to 19.7%) caused by possible hydraulic disturbance from proximal to distal regions. Therefore, our findings indicate that the tap water bacteria could possibly be managed by selecting and operating the purification process properly and cleaning the distribution system effectively.

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Aim:  Identification of the predominating cultivable bacteria in granular activated carbon (GAC) filters used in a variety of water treatment plants for selecting representative strains to study the role of bacteria in the removal of dissolved organic matter. Methods and Results:  Bacterial isolates were collected from 21 GAC filters in nine water treatment plants treating either ground water or surface water with or without oxidative pretreatment. Enrichment of samples in dilute liquid medium improved culturability of the bacteria by approximately log unit, to 9% up to 70% of the total cell counts. Genomic fingerprinting and 16S rDNA sequence analysis revealed that most (68%) of the isolates belonged to the Betaproteobacteria and 25% were identified as Alphaproteobacteria. The number of different genera within the Betaproteobacteria was higher in the GAC filters treating ozonated water than in the filters treating nonozonated water. Polaromonas was observed in nearly all of the GAC filters (86%), and the genera Hydrogenophaga, Sphingomonas and Afipia were observed in 43%, 33% and 29% of the filter beds, respectively. AFLP analysis revealed that the predominating genus Polaromonas included a total of 23 different genotypes. Conclusions:  This study is the first to demonstrate that Polaromonas, which has mainly been observed in ultraoligotrophic freshwater environments, is a common component of the microbial community in GAC filters used in water treatment. Significance and Impact of the Study:  The predominance of ultraoligotrophic bacteria in the GAC filters indicates that very low concentrations of substrates are available for microbial growth. Polaromonas species are suited for further studies on the nutritional versatility and growth kinetics enabling the modelling of biodegradation processes in GAC filters.

Understanding the fate of effluent organic matter (EfOM) and natural organic matter (NOM) through riverbank filtration is essential to assess the impact of wastewater effluent on the post treatment requirements of riverbank filtrates. Furthermore, their fate during drinking water treatment can significantly determine the process design. The objective of this study was to characterise bulk organic matter which consists of EfOM and NOM during riverbank filtration using a suite of innovative analytical tools. Wastewater effluent-derived surface water and surface water were used as source waters in experiments with soil columns. Results showed the preferential removal of non-humic substances (i.e. biopolymers) from wastewater effluent-derived surface water. The bulk organic matter characteristics of wastewater effluent-derived surface water and surface water were similar after 5 m soil passage in laboratory column experiment. Humic-like organic matter in surface water and wastewater effluent-derived surface water persisted through the soil passage. More than 50% of total dissolved organic carbon (DOC) removal with significant reduction of dissolved oxygen (DO) was observed in the top 50 cm of the soil columns for both surface water and wastewater effluent-derived surface water. This was due to biodegradation by soil biomass which was determined by adenosine triphosphate (ATP) concentrations and heterotrophic plate counts. High concentrations of ATP in the first few centimeters of infiltration surface reflect the highest microbial activity which correlates with the extent of DOC reduction. Good correlation of DOC removal with DO and biomass development was observed in the soil columns.