Four different types of alkaline chemicals consist of Ca(OH)2,
NaOH, Na2CO3 and CaCO3 were used to neutralize the solution pH
after adding PAC. NaOH was added as 0.1 mol/L solution while
others were powder. As it can be seen from Fig. 3 that CaCO3
provided the highest removal of HA (96.6%) and DOC (91.6%) when
compared to other alkaline chemicals. It seems that CaCO3
particles were to be the
flock core. Therefore, the
flock formation
was promoted and the high removal efficiency was achieved. This
effect is due to the remaining CaCO3 acting as a coagulant aid by
forming larger
flocks which provide a relatively shorter settling
time for the removal of DOC [33–35].