Arsenic Removal from Groundwater using Ferric

Arsenic is a carcinogenic metalloid that is currently regulated in drinking water. The levels of arsenic in finished water in an existing water treatment plant are exceeding the current regulation of 10 μg/L. One of the available technologies for arsenic removal from groundwater is adsorption onto coagulated flocs and in this field, ferric chloride is the most commonly used coagulant for arsenic removal. This research work was conducted to explore a suitable conventional treatment technology for arsenic removal from given groundwater in order to reduce the filtrate arsenic concentration to less than 10 μg/L. Bench scale jar test experiments and pilot-scale investigations were carried out to evaluate and improve the coagulation/flocculation process for arsenic removal using ferric chloride. Model water that represented the water from the existing water treatment plant was used to investigate the effects of different conditions of pH, coagulant doses, arsenic speciation, initial arsenic concentration, temperature, and flocculation conditions on the arsenic removal efficiency by coagulation/flocculation process. Based on these bench scale experiments, a direct filtration technique to separate the formed flocs was considered as the most suitable floc separation system to be applied after coagulation/flocculation process. A direct filtration pilot plant was operated to evaluate the efficiency of arsenic removal. The results of series of jar test experiments showed that As(V) could be completely removed with iron doses higher than 2 mg/L for filtered samples and at pH value about 7.0. The lower efficiencies obtained for unfiltered samples indicate that settling mechanisms are not effective enough to ensure complete removal of As(V), even when using very high doses of coagulant. In agreement with the results of previous studies, it was found that As removal efficiency increased with the coagulant dose. Additionally it was also observed that under the given conditions As(III) removal efficiency was much lower (up to 60%) compared to As(V) removal efficiency (90 100%). Direct filtration with iron doses of 2 mg/L at pH value about 7.0, could reduce As(V) levels from 50 μg/L to 4 μg/L or less without any risk of iron or turbidity increasing in the filtered water within a reasonable filterrun length. Direct filtration using ferric chloride as coagulant, could be an appropriate technology to reduce arsenic levels below 10 μg/L for the given groundwater.