Hi all…with advancements in molecular methods/genomics, microbial surveys are becoming much more affordable and are showing up in the literature more frequently. Since the adoption of biological filtration there has been strong interest in the bacterial consortia found in such filters. In a recent study in Saskatchewan researchers used 16S rRNA profiling to describe the bacterial communities in water entering two small drinking WTPs, both of which use surface water as their water source. Both plants employed ozone and had some form of biological filtration.
They found “that the bacterial consortia in each water source are compositionally distinct and that the predominant bacterial groups change with seasonality. A further evaluation of the microbial communities…within a biological activated carbon (BAC) filter revealed a dramatic shift in community composition from raw water and that Legionella, Pseudomonas, Aeromonas, and especially Mycobacterium established within the filter. Our work suggests that BAC filters may provide a suitable niche favouring the accumulation of some bacteria, making disinfection post-filtration and the maintenance of disinfectant residuals throughout the distribution system critical to ensuring safe potable water for rural communities.”
I think that it is generally accepted that bacteria differ from one source water to another; however, while bacterial activity declines with temperature, it wasn’t clear whether the bacterial community substantially changed or if it was simply less active. It is notable that they found the opportunistic pathogens Legionella, Pseudomonas, Aeromonas, and Mycobacterium established within the filters although I’ve seen all of these (except Legionella) in drinking water filters in Canada. Another interesting observation was that very few enteric coliforms were identified in the source waters they tested. This would be highly unusual in most surface waters.
Bill
_______________________________________________________________
From source to filter: changes in bacterial community composition during potable water treatment
Enisa Zanacic, Dena W. McMartin, John Stavrinides
Canadian Journal of Microbiology, 2017, 63(6): 546-558, http://www.nrcresearchpress.com/doi/abs/10.1139/cjm-2017-0077#.WTAM000VCpo
Abstract
“Rural communities rely on surface water reservoirs for potable water. Effective removal of chemical contaminants and bacterial pathogens from these reservoirs requires an understanding of the bacterial community diversity that is present. In this study, we carried out a 16S rRNA-based profiling approach to describe the bacterial consortia in the raw surface water entering the water treatment plants of 2 rural communities. Our results show that source water is dominated by the Proteobacteria, Bacteroidetes, and Cyanobacteria, with some evidence of seasonal effects altering the predominant groups at each location. A subsequent community analysis of transects of a biological carbon filter in the water treatment plant revealed a significant increase in the proportion of Proteobacteria, Acidobacteria, Planctomycetes, and Nitrospirae relative to raw water. Also, very few enteric coliforms were identified in either the source water or within the filter, although Mycobacterium was of high abundance and was found throughout the filter along with Aeromonas, Legionella, and Pseudomonas. This study provides valuable insight into bacterial community composition within drinking water treatment facilities, and the importance of implementing appropriate disinfection practices to ensure safe potable water for rural communities.”
