Biological filtration for removal of arsenic from drinking water.

The main objective of the study was to find a suitable iron to arsenic ratio in water to reduce arsenic to 5 microg/L or lower through sand filtration. Experiments were conducted by varying the quantity of iron(II) while keeping the arsenic concentration at 100 microg/L. A mixture of iron (II) and arsenic at different ratios (10:1, 20:1, 30:1 and 40:1) was pumped to the sand filters in a down flow mode and effluent arsenic and iron were analyzed. It was found that a ratio of iron to arsenic of 40:1 was necessary to ensure an effluent arsenic concentration of 5 microg/L or lower. Iron in the filtrate was found to be below 0.1 mg/L at all times.