The filtrates were tested for Se concentration. A small
amount of sample was taken immediately to measure Zeta potential
(Zetasizer 2000, Malvern, UK) during the slow mix period.
Before the coagulant dose a predetermined amount of 0.2 mol/L
NaOH or 0.05 mol/L HCl solution was added into water samples
to approximately get an expected pH value. After dosing with coagulants,
water pH was accurately adjusted to the expected value
during the rapid mix period by adding HCl or NaOH solution, after
which the water pH was constant during the subsequent flocculation
process.