Comparison of the effects of ozone, biological activated carbon (BAC) filtration and combined ozone-BAC pre-treatments on the microfiltration of secondary effluent

The effects of ozonation (O-3), biological activated carbon (BAC) filtration and combined O-3 and BAC (O-3-BAC) pre-treatments on the microfiltration (MF) treatment of secondary effluent using a polyvinylidene fluoride (PVDF) membrane were studied. The permeability of the membrane was quantified and compared to the removal of humic substances (HS), biopolymers (BPs), dissolved organic carbon (DOC), absorbance at 254 nm (UVA(254)), and colour by these pre-treatments. The apparent molecular weight distribution (AMWD) was determined to further characterise the secondary effluent before and after each treatment. The unified membrane fouling indices (UMFI) after O-3, BAC and the O-3-BAC pre-treatments were also determined to evaluate the relative effectiveness of different pre-treatments on fouling reduction. The overall removal of colour and UVA(254) in the MF of the O-3 pre-treated secondary effluent was found to be 83% and 52% respectively, compared to 75% and 47% respectively for MF with BAC pre-treatment and 38% and 14% respectively without pre-treatment. The O-3-BAC pre-treatment yielded the highest normalized permeability after 100 min of operation (0.76) and the lowest UMFI (1 x 10(-3) m(2)/L). This result indicates that the O-3-BAC pre-treatment could reduce the frequency of chemical cleaning and may extend the membrane lifetime.