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MASS TRANSPORT WITHIN BACTERIAL BIOFILMS

Spatial distribution of local mass transfer co-efficient above and within biofilms was measured using a microsensor based on limiting current technique. The mass transfer coefficients measured within microbial clusters and within interstitial voids were significantly different. Measurement of local flow velocities near the microsensor's tip using Particle Image Velocimetry in conjunction with the Confocal Scanning Laser Microscope permitted us to quantify the relation between the hydrodynamics, and mass transfer coefficient at specific locations above and within the biofilm.

It is becoming apparent that mass transport within biofilms is much more complex than previously assumed as 1 ) the biofilm itself is heterogenous and consists of discrete cell clusters separated by interstitial voids; 2) the hydrodynamics in the biofilm region is controlled by two flow fields; and 3) the mass transfer coefficient behaves unexpectedly in the biofilm. Although the newly proposed concept of biofilm structure helps to interpret the experimental observations, the new experiments reveal further dimensions of complexity.

We are becoming progressively aware that it may not be possible to completely describe mass transport in biofilm systems mathematically. Some simplifying assumptions are, therefore, urgently needed to establish empirical equations serving purely practical purposes. It is important that these assumptions are established as a result of careful experimentation rather than convenience.

Key words: biofilm, biofilm structure, biofilm activity,