Effects of different Ca2+ behavior patterns in the electric field on membrane fouling formation and removal of trace organic compounds

The effects of Ca2+ on membrane fouling and trace organic compounds (TrOCs) removal in an electric field-assisted microfiltration system were investigated in the presence of Na+alone for comparison.In the electric field,negatively charged bovine serum albumin (BSA)migrated towards the anode far away from the membrane surface,resulting in a 42.9％ trans-membrane pressure (TMP) reduction in the presence ofNa+ at 1.5 V.In contrast,because of the stronger charge shielding of Ca2+,the electrophoretic migration of BSA was limited and led to a negiectable effect of the electric field (1.5 V) on membrane fouling.However,un-der 3 V applied voltage,the synergistic effects of electrochemical oxidation and bridging interaction between Ca2+ and BSA promoted the formation of denser settleable flocs and a thinner porous cake layer,which alleviated membrane fouling with a 64.5％ decrease in TMP and nearly 100％ BSA removal.The TrOCs elimination increased with voltage and reached 29.4％-80.4％ at 3 V.The electric field could prolong the contact between TrOCs and strong oxidants generated on the anode,which enhanced the TrOCs removal.However,a stronger charge shielding ability of Ca2+ weakened the electric field force and thus lowered the TrOCs removal.