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7.5 Trouble Shooting
7.5.1 MBR Membrane Fouling
Introduction
MBR operation relies critically on the ability of the membrane unit to pass all flow incoming to
the plant. If membrane permeability is impaired, the MBR plant cannot process all flow with
potentially catastrophic results even though effluent quality remains consistently high. This
contrasts with typical operation of activated sludge system where the plant hydraulic capacity is
rarely exceed but effluent quality is much more variable. Hence, membrane fouling (and
associated reduction of flux or increase of TMP) remains as an operational challenge.
Membrane Fouling in MBR is a result of the interaction between the incoming water quality,
mixed liquor filterability, system operation condition, and membrane material. There are four
categories of membrane fouling. They are microbial fouling, particle/colloids fouling, inorganic
fouling, and organic fouling. A brief description on the nature of fouling and control measures is
summarized below.
7.5.1.1 Microbial/Biological Fouling
Microbial fouling is a result of formation of biofilms on membrane surfaces. Living materials,
such as bacteria, fungus and algae, or soluble microbial products (SMP) and extracellular
polymetric substances (EPS) bound to the activated sludge attach to the membrane; they start
to multiple and produce EPS to form a viscous, slimy, hydrated gel. EPS typically consists of
heteropolysaccharides and have high negative charge density. This gel structure protects
bacterial cells from hydraulic shearing and from chemical attacks of biocides such as chlorine.
7.5.1.2 Particulate/colloid Fouling
This type of fouling may be associated with high concentrations of colloidal solids present in
mixed liquor. In most cases, particles and colloids do not really foul the membrane because the
flux decline caused by their accumulation on the membrane surface is largely reversible by
hydraulic cleaning measures such as backwash and air scouring. However, the accumulation of
solids between the membranes can create increased membrane resistance to permeation and
permanent physical membrane damage.
To distinguish the different fouling phenomena, particles and colloids here are referred to
biologically inert particles and colloids that are inorganic in nature.
newterra O&M Manual
109
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