4.1 Biofouling Mechanism
Unwanted deposition and growth of biofilm are
commonly embedded on a membrane surface in a
matrix of microbial origin, consisting of extra-cellular
polymeric substances (EPS) and microorganisms [11].
The formation of a biofilm in an aqueous environment
generally proceeds in the following sequence [12]-[14]
(Figure 2):
1) When organic matter is presented, a
conditioning film of adsorbed components is formed
on the membrane surface prior to the arrival of the
first microorganisms.
2) Microorganisms are transported to the surface
through diffusion, convection, sedimentation or active
movement. This step is the initial step of membrane
biofouling.
3) Initial microbial adhesion occurs when EPS
is synthesized to protect and stabilize cell attachment
from the outside environmental effects.
4) Attachment of adhering micro-organisms is
strengthened through EPS production and unfolding
of cell surface structures.
5) Growth and metabolism of the attached
microorganisms and film develop, and continue
secretion of exo-polymers or biopolymer.
6) Localized detachment of biofilm organisms
caused by occasionally high fluid shear or other
detachment forces operative starts after initial
adhesion, although adhesion of individual
microorganism is frequently considered irreversible
(whether justified or not), and increase with time
as it is related to the number of microorganisms
present in the biofilm