Compared to the Conventional Activated Sludge Process (ASP), Membrane Bioreactors (MBRs) have
proven their superior performance in wastewater treatment and reuse during the past two decades. Further,
MBRs have wide array of applications such as the removal of nutrients, toxic and persistent organic pollutants
(POPs), which are impossible or difficult to remove using ASP. However, fouling of membrane is one of the
main drawbacks to the widespread application of MBR technology and Extra-cellular Polymeric Substances
(EPS) secreted by microbes are considered as one of the major foulants, which will reduce the flux (L/m2/h)
through the membrane. Critical flux is defined as the flux above which membrane cake or gel layer formation
due to deposition of EPS and other colloids on the membrane surface occurs. Thus, one of the operating
strategies to control the fouling of MBRs is to operate those systems below the critical flux (at Sub-Critical
flux). This paper discusses the critical flux results, which were obtained from short-term common flux step
method, for a lab-scale MBR system treating Ametryn. This study compares the critical flux values that were
obtained by operating the MBR system (consisting of a submerged Hollow-Fibre membrane with pore size of
0.4μm and effective area of 0.2m2) at different operating conditions and mixed liquor properties. This study
revealed that the critical flux values found after the introduction of Ametryn were significantly lower than those
of obtained before adding Ametryn to the synthetic wastewater. It was also revealed that the production of
carbohydrates (in SMP) is greater than proteins, subsequent to the introduction of Ametryn and this may have
influenced the membrane to foul more. It was also observed that a significant removal (40-60%) of Ametryn
from this MBR during the critical flux determination experiments with 40 minutes flux-step duration
