a b s t r a c tLittle is known about the forces that determine the assembly of diverse bacterial communities inhabiting drinking water treatment filters and how this affects drinking water quality. Two contrasting ecological theories can help to understand how natural microbial communities assemble; niche theory and neutral theory, where environmental deterministic factors or stochastic factors predominate respectively. This study investigates the development of the microbial community on two common contrasting filter materials (quartz sand and granular activated carbon-GAC), to elucidate the main factors governing their assembly, through the evaluation of environmental (i.e. filter medium type) and stochastic forces (random deaths, births and immigration). Laboratory-scale filter columns were used to mimic a rapid gravity filter; the microbiome of the filter materials, and of the filter influent and effluent, was characterised using next generation 16S rRNA gene amplicon sequencing and flow-cytometry. Chemical parameters (i.e. dissolved organic carbon, trihalomethanes formation) were also monitored to assess the final effluent quality. The filter communities seemed to be strongly assembled by selection rather than neutral processes, with only 28% of those OTUs shared with the source water detected on the filter medium following predictions using a neutral community model. GAC hosted a phylogenetically more diverse community than sand. The two filter media communities seeded the effluent water, triggering differences in both water quality and community composition of the effluents. Overall, GAC proved to be better than sand in controlling microbial growth, by promoting higher bacterial decay rates and hosting less bacterial cells, and showed better performance for putative pathogen control by leaking less Legionella cells into the effluent water.
We collected urban soil samples impacted by polycyclic
aromatic
hydrocarbons (PAHs) from a sorbent-based remediation field trial to
address concerns about unwanted side-effects of 2% powdered (PAC)
or granular (GAC) activated carbon amendment on soil microbiology
and pollutant biodegradation. After three years, total microbial cell
counts and respiration rates were highest in the GAC amended soil.
The predominant bacterial community structure derived from denaturing
gradient gel electrophoresis (DGGE) shifted more strongly with time
than in response to AC amendment. DGGE band sequencing revealed the
presence of taxa with closest affiliations either to known PAH degraders,
e.g.
Rhodococcus jostii
RHA-1, or taxa known to harbor
PAH degraders, e.g.
Rhodococcus erythropolis,
in
all soils. Quantification by real-time polymerase chain reaction yielded
similar dioxygenases gene copy numbers in unamended, PAC-, or GAC-amended
soil. PAH availability assessments in batch tests showed the greatest
difference of 75% with and without biocide addition for unamended
soil, while the lowest PAH availability overall was measured in PAC-amended,
live soil. We conclude that AC had no detrimental effects on soil
microbiology, AC-amended soils retained the potential to biodegrade
PAHs, but the removal of available pollutants by biodegradation was
most notable in unamended soil.
This paper describes a novel, composite device, based not on optical excitation but on the transfer of holes from Si to the TiO(2)/air or TiO(2)/water interface, for the disinfection and detoxification of fluid streams.
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