flow; mass transport; and biofilm clusters?
stephen at livesey123.freeserve.co.uk
Wed Oct 11 14:12:43 EST 2000
I have been studying the effects of recirculation flow velocity (within a
rectangular channel, 2cm * 10cm) on the rate of autotrophic
denitrification. I would like to present some observations and ask for comment.
I have observed the following:
 at low flow rates Re ~ 300 a compact flat biofilm morphology may be
 when the flow is progressively increased (Re~300-2400) the presence of
anchored clusters of biomass becomes evident. The clusters oscillate/waft
in the flow.
 further increasing the flow rate to Re~3000 leads to a significant drop
in reactor performance (probably due to sloughing).
Analysis of the mass transport of nitrate (NO3-) in the system by relating
mass flux to the hydraulic conditions (using Sherwood no.eqns 1 and 2),
suggested that the system is not under mass transfer control.
(calculated mass flux of N03- was an order of magnitude greater than the
experimentally observed flux).
 Sh = 1.8488*((Re*Sc*de)/L)^1/3 -0.4
Prasad et al., 1995 flow in rectangular channel.
 N (mol/m2s) = ((Sh*D)/de)*Cb
where Re =Reynolds no.; Sc = Schmidt no.; de= equivalent hydraulic diameter
(m); L = length of channel(m); D = diffusion coeff.(m2/s); and Cb= bulk
Nevertheless the rate of denitrification was observed to increase almost
linearly with increasing flow rate. This suggested that another mechanism
was enhancing the rate of denitrification.
My question is: has anyone made similar observations; read of mechanisms by
which oscillation of anchored clusters of biomass have enhanced reaction
rates; or have suggestions for the observed results?
I was thinking that the movement of the clusters is in someway reducing
diffusion limitations within the biofilm. Anyway as you can imagine I would
be greatful for any comments.
To reply to the group as well as to the originator, make sure that
the address biofilms at net.bio.net is included in the "To:" field.
See the BIOFILMS homepage at http://www.im.dtu.dk/biofilms for info
on how to (un)subscribe and post to the Biofilms newsgroup.
More information about the Biofilms