In this thesis it is investigated how the di?erent components in sludge from a membrane
bioreactor (MBR) affect each other during the fouling process that occurs during
membrane filtration. This is done to confirm the hypothesis that the content of
extracellular polymeric substances (EPS) and colloids reduces the flux through the
membrane, whereas flocs and powdered activated carbon (PAC) increases the flux through
the membrane because of the scouring effect.
In order to obtain a confrmation of this, experiments have been performed by MBR
filtration of sludge containing different concentrations of the three sludge fractions (EPS,
colloids, and flocs), along with experiments with sludge and supernatant containing PAC.
The fractionation of sludge is performed by centrifugation for 8min at 3400g in order to
separate the flocs and filtration through a mixed cellulose membrane in order to separate
the colloids.
The experiments is performed by 1hour filtration at each of seven transmembrane
pressures (TMPs), with 1hour relaxation phase between each ?ltration. The experiments
is performed in a laboratory-scale MBR at Aalborg University and the MBR sludge is
obtained from Aalborg vest wastewater treatment plant and Grundfos Biobooster facility
in Bjerringbro.
The results of the experiments confirm that EPS and colloids reduces the flux through
the membrane, whereas the ratio C floc /(C colloid +C EPS ) increases the flux through the
membrane. However, there was only a limited positive effect of the addition of PAC.
Furthermore, it can be concluded that the cake layer that is formed on the membrane is
more compact and compressible at increased concentrations of EPS and colloids, whereas
a less compact and compressible cake layer is formed when the concentration of flocs is
increased.