Influence of Iron Salts Pre-coagulation on Fouling of Microfiltration Membrane

To optimize the iron pre-coagulation condition and clarify the influence of different aggregates characteristics on membrane fouling for coagulation- microfiltration (MF) process, pre-coagulation conditions of ferric chloride (FC) and polymeric ferric sulfate (PFS) at different coagulant dosages (0. 1, 0.2, 0.4, 0.6 mmol/L) and coagulation pH values (4.5, 5.5, 6.5, 7.5) were analyzed to reveal membrane fouling mechanisms and humic acid removal.Resultsshow that under acidic pH 4. 5-5. 5 of electrical neutralization coagulation condition, the lower PFS dosage (0. 1- 0. 2 mmol/ L) has the better coagulation effect, which the agglomerates have larger particle size and higher fractal dimension for more high positive charge produced by polymeric ferric hydrolysis products have an advantage in charge neutralization in comparison with FC. Thus membrane flux declination is slowed down and membrane fouling is alleviated. Under neutral pH 6. 5- 7. 5 of sweep coagulation, the higher dosage (0. 4-0. 6 mmol/ L) of FC is superior to reduce membrane fouling, as hydrolysis products of FC is liable to produce larger particles in sweep coagulation. Particle size and structural characteristics of the coagulation agglomerates directly affect the membrane fouling, the larger particle size and higher fractal dimension are superior to increase membrane flux and simultaneously improve water quality.