2.7. Column test
The silica sand samples were sieved, washed, air-dried, and sterilized
before the experiments. The pH of the sand suspended in
distilled water was 8.5. The heavy metal bioremediation studies
were performed in 50 mm diameter and 500 mm length columns
(OMG Chemical Co., Korea), containing 1.0 kg silica sand supplemented
with 2 mM mixture of heavy metals. The heavy metals were
thoroughly mixed into the sand while in solution form. The bacterial
mixtures culture (A3, equivalent to 108 CFU/mL) was grown
overnight in YA broth. The control treatment consisted of the same
set-up as the experimental treatment but without the addition of
bacterial cells. Bioremediation was determined by measuring the
time required for 100 mL of 5 mM urea and 25 mM calcium chloride
to pass through the column. The experiment was performed
at room temperature (25 ◦C) and run for 3 d. After the experiment