NAMS 2002 Workshop - ICOM 2008

Membrane Fouling - General Topics – 4
Monday July 14, 11:15 AM-11:45 AM, O’ahu
MBR Activated Sludge Filterability Alteration in Stress Circumstances
S. Geilvoet (Speaker), Delft University of Technology, The Netherlands, s.p.geilvoet@tudelft.nl
J. Van der Graaf, Delft University of Technology, The Netherlands
A. Van NIeuwenhuijzen, Delft University of Technology, The Netherlands
Fouling in membrane bioreactor (MBR) systems is an extensively investigated
research topic. Significant progress has been made in understanding fouling, but
nevertheless it still is a major point of attention in full-scale MBR operation and
many questions still remain unanswered. Simply stated the fouling potential in a
membrane bioreactor (MBR) system is depending on three factors: membrane
properties, membrane operation and activated sludge properties. Because in
practice every MBR plant has its own unique combination of these three factors,
it is difficult to determine which factor(s) is/are responsible in case of fouling
problems. Delft University of Technology has developed a filtration
characterization method that aims at determining the role of sludge
characteristics in the filtration process. Sludge samples collected from different
full-scale MBR plants or under different circumstances are filtrated with the same
membrane under exact identical operational circumstances with the Delft
Filtration Characterization method (DFCm). In this way differences in filterability
can be related exclusively to the quality of the sludge sample.
Several researchers demonstrated that when activated sludge is experiencing
stress conditions severe fouling problems can occur. In this research two
different stress conditions were simulated. Activated sludge samples collected
from full-scale MBR Heenvliet in the Netherlands were exposed to a long period
without aeration and to a short period of high shear stress conditions induced by
a centrifugal pump. Goal of the research was to examine the effect of these
stress conditions on the sludge filterability and characteristics and the ability of
the sludge to recover from it. The filtration characterization experiments were
accompanied by several sludge quality analyses: the concentration Soluble
Microbial Products (SMP), Particle Size Distribution (PSD) in the submicron
range of the free water and sludge viscosity were measured.
The results show that exposing the sludge to stress conditions lead to
deflocculation of the sludge which was expressed in the release of SMP and of
colloidal particles in the free water and a deterioration of the filterability. When
the sludge was subsequently preserved in continuous aerated conditions, it
showed a strong ability to recover from the stress circumstances. The sludge
quality deterioration which was obtained in approximately three days of anoxic
circumstances was undone in a period of only several hours. Together with the