NAMS 2002 Workshop - ICOM 2008

of the flexibility of their external membrane (Escherichia coli, Pseudomonas
aeruginosa, Staphylococcus aureus, Brevundimonas diminuta and Micrococcus
luteus). Dead-end filtration experiments, in a stirred filtration cell, were carried out
with bacterial suspensions of each strain at 104 CFU/mL as feed solutions.
Transmembrane pressure was set at 0.5 bar for all trials. Steadily, filtration flux
was measured and permeate samples were collected. Viable bacteria were then
enumerated after culture into solid nutrient agar medium (24 h at 37 °C).
According to the results of those trials, the assessment of the presence of
bacteria in the permeates has allowed to associate each strain to one only of the
homoporous membranes tested. The interesting feature is that there is not a
direct correspondence between the size of the pores (homoporous membranes)
and the size of the bacteria, and this because of the deformation of the latter
during the filtration process. Moreover, since when several bacteria are present
in a dispersion they do not exhibit the same rejection as when they are filtered
one by one, successive filtrations of each bacterial suspension are ncessary to
accurately assess the presence of the largest pores in the structure of a tested
membrane and to evaluate the range of their diameter.
For instance, if an unknown membrane fully retains Escherichia coli, we can
consider that defects of 0.4 µm in diameter are not enough numerous to alter the
membrane removal capacity. If this tested membrane leaks Pseudomonas
aeruginosa to some extent, one concludes that the presence of pores of at least
0.2 µm is not negligible. The application of this methodology to various
commercial ultrafiltration membranes and to membranes with a controlled
porosity will be presented.
To conclude, in complement to other characterisation tests, this methodology
could be a well-adapted tool to qualify filtration membranes or modules in terms
of bacterial removal efficiency and to carry out unbiased comparison between
membranes in a benchmarking context.
References
[1] Causserand et al. 2002 - Desal vol.149 p.485.
[2] Shinde et al. 1999 - J Membr Sci vol.162, p.9.
[3] Kobayashi et al. 1998 - J Membr Sci vol.140 p.1.
[4] Farahbakhsh 2003 - JAWWA vol.95 p.95.
[5] Urase et al. 1996 - J Membr Sci vol.115, p.21.
[6] Delebecque et al. 2006 - Desal vol.199 p.81.