P. Stoodley et al., OSCILLATION CHARACTERISTICS OF BIOFILM STREAMERS IN TURBULENT FLOWINGWATER AS RELATED TO DRAG AND PRESSURE-DROP, Biotechnology and bioengineering, 57(5), 1998, pp. 536-544
Mixed population biofilms consisting of Pseudomonas aeruginosa, P. flu
orescens, and Klebsiella pneumoniae were grown in a flow cell under tu
rbulent conditions with a water flow velocity of 18 cm/s (Reynolds num
ber, Re, = 1192). After 7 days the biofilms were patchy and consisted
of cell clusters and streamers (filamentous structures attached to the
downstream edge of the clusters) separated by interstitial channels.
The cell clusters ranged in size from 25 to 750 mu m in diameter. The
largest clusters were approximately 85 mu m thick. The streamers, whic
h were up to 3 mm long, oscillated laterally in the flow. The motion o
f the streamers was recorded at various flow velocities up to 50.5 cm/
s (Re 3351) using confocal scanning laser microscopy. The resulting ti
me traces were evaluated by image analysis and fast Fourier transform
analysis (FFT). The amplitude of the motion increased with flow veloci
ty in a sigmoidal shaped curve, reaching a plateau at an average fluid
flow velocity of approximately 25 cm/s (Re 1656). The motion of the s
treamers was possibly limited by the flexibility of the biofilm materi
al. FFT indicated that the frequency of oscillation was directly propo
rtional to the average flow velocity (u((ave))) below 9.5 cm/s (Re 629
). At u((ave)) greater than 9.5 cm/s, oscillation frequencies were abo
ve our measurable frequency range (0.12-6.7 Hz). The oscillation frequ
ency was related to the flow velocity by the Strouhal relationship, su
ggesting that the oscillations were possibly caused by vortex shedding
from the upstream biofilm clusters. A loss coefficient (k) was used t
o assess the influence of biofilm accumulation on pressure drop. The k
across the flow cell colonized with biofilm was 2.2 times greater tha
n the k across a clean flow cell. (C) 1998 John Wiley & Sons.