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by aerosolizinga5mL aliquot (1.0 × 107
spores/mL) of a
commercial suspension (CIP77.18, Pasteur Institute, Paris)
into the reaction chamber as droplets in a high flow rate air
stream using a peristaltic pump (6.4 × 107
microorganismsMicroorganism Numeration. Direct quantitative analy-
sis of bacteriawas achieved by epifluorescencemicroscopy
using the “LIVE/DEAD Baclight Bacterial Viability kit”
(Invitrogen) as appropriate viability indicator and staining
method based on a membrane integrity test for easily
distinguishing between live (with integrate membranes)
and dead cells (with damaged ones), whatever their
cultivability (5). Thus, the treatment efficiency can be
directly derived fromthe viabilities (expressed in percents)
at the inlet and the outlet of a photoreactor. This method
is not suitable to viability of bacterial spores and the
infectivity of viruses.However, since suchmicroorganisms
do not enter a “viable but noncultivable state” (VBNC),
their counts can be performed using classical heterotrophic
plate count. Details can be found in a review dealing with
numeration methods (5) and as SI S4.
Efficiency Indicator.The efficiency of a biocidal treatment
for disinfecting liquids or surfaces was usually described
with the “logarithmic reduction” (LR). This indicator com-
pared the concentrations before and after the treatment, so
that the treatment efficiency was defined by this ratio, and
expressed on a log10 scale for overcoming the low precision
of biological numerations. However, this calculation could
not be used here, since the numeration should be performed
over the totality of the bacteria.
Thus, the viability of the bacteria bioaerosol could be
defined as the ratio between live bacteria and both live and
dead bacteria in an air flow sampling. The bacteria viability
in the inlet air corresponded to the viability of the starting
suspension (µin), whereas the bacteria viability in the outlet
air corresponded to the viability of the collected suspension
(µout). The absence of any influence of both aerosolization
and collection processes on the bacteria viability has been
checked. The LR could be easily expressed using this
percentage viability, and thus be replaced by the logarithmic
reduction in viability (LRV) which considers that a virtual
quantity ofmicroorganismsN0 entered the photoreactorwith
a µin viability and left it with a µout one (eq 1).Results and Discussion
Computational Fluid Dynamics (CFD) Study Applied to
Annular Photoreactors. If annular photocatalytic reactors
are irreplaceable for theoretical studies in the case of chemical
applications because they enable determining the kinetic
parameters and validating themechanismswhich can further
be incorporated in CFD models, their efficiency for the
removal of AMOs at high flow rates remains questionable.
In order to illustrate that, the motion of spherical particles
inside an annular photoreactor has been simulated using
the “Fluent”CFDsoftware, as a function of the annular space
and of the particle size ranging from 10 nm to 10 µm, at a
constant flow rate of 5 m3
/h (Figure 2). In such a configu-
ration, the photocatalytically active contact surface cor-
responded to the internal side of the external tube, with the
flow passing through the inner space between both coaxial
tubes, the inner tube being in ourmodel the external surface
of the UV-A actinic lamp tube.
For this computation, no reactions have been incorpo-
rated in the model, the particles hitting the internal surface
of the external wall being simply “trapped” on the photo-