Pre-treatments for removing colour from secondary effluent: Effectiveness and influence on membrane fouling in subsequent microfiltration

The effects of different pre-treatments for colour removal on membrane fouling in the microfiltration (MF) of a coloured activated sludge (AS) effluent were investigated. It was found that a 80% colour removal target could be achieved by pre-treatment of the raw AS effluent with either ozone (10 mg O3 L−1, 10-min contact time), a powdered activated carbon (150 mg L−1, 30-min contact time), or a strong base anion exchange resin (10 mL L−1, 20-min contact time). Of these pre-treatments, ozonation was the only method that resulted in a reduction in membrane fouling. The other two methods, while they showed high removals of dissolved organic matter, did not affect the membrane flux. The changes in the membrane foulants due to the pre-treatments were determined and were used to explain the differences in the membrane flux. The results showed that pre-treatments for fouling reduction in MF of secondary effluent should target the biopolymers (which contained polysaccharides and proteins) in the effluent.

► Decolourisation of secondary effluent by ozonation and adsorption.
► Ozonation reduced membrane fouling in microfiltration of the effluent.
► Anion exchange resin and powdered activated carbon treatment did not reduce fouling.
► Membrane foulants were polysaccharides, proteins, and humic substances.
► Fouling reduction was due to breakdown in structures of the foulants.