2.7. Column test The silica sand samples were sieved, washed, air dried, and sterilized before the experiments. The pH of the sand suspended indistilled 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 bacte-rial mixtures culture (A3, equivalent to 108CFU/mL) was grown overnight in YA broth. The control treatment consisted of the same setup as the experimental treatment but without the addition of bacterial cells. Bioremediation was determined by measuring thetime required for 100 mL of 5 mM urea and 25 mM calcium chlo-ride to pass through the column. The experiment was performedat room temperature (25◦C) and run for 3 d. After the experimentended, the effluent samples were collected from the bottom of thecolumn with 100 mL of distilled water. The concentrations of heavymetals in the effluent samples were determined by ICP-OES.