Impact of sludge cation distribution pattern on its filterability in membrane bioreactor

The distributions of cations of various valences (Na+, Ca2+ and Fe3+) in the outer layers of extracellular polymeric substances (EPSs) to pellet have a significant impact on the stratification structure of polysaccharides (PS) or proteins (PN) in activated sludge. Comparison with the control showed that the monovalent Na+ reduced flocculability slightly (about 9.75%), whereas Ca2+ and Fe3+ increased flocculability significantly. The modified fouling index (MFI) had a significant correlation with PN in the supernatant (rp = 0.8593), slime (rp = 0.7218) and loosely bound EPS (LB, rp = 0.8012). However, it had a moderate correlation with PS in supernatant (rp = 0.5842), and weak correlation to slime (rp = 0.3785) or LB (rp = 0.3219). There was an ignored correlation with PN or PS in the tightly bound EPS (TB) or pellet. The lower amount of PN or PS in the supernatant would have positive impact on improving the activated sludge filterability.