with MBR, anything can ...

with MBR, anything can happen. Your requirement is just very stringent and its very costly. You will have to use a smaller membrane(say 0.2micron) where a pigment can be prevented to go with the effluent. In this case, your overhead /vertical height of the MBR tanks must be very high (maybe 10 times) as the height holds a bigger body of water that pushed the liquor to the membrane. I say again Mr Jacob that its very costly. At 0.2micron, any micro organisms are prevented, inorganic matters and most of the organics.