Human exposure to the toxic element arsenic due to consumption of arsenic contaminated water is still a global issue worldwide. Conventional treatment techniques are not very efficient at removing arsenite, which is the predominant species of arsenic in raw groundwater. Biological oxidation of arsenite by arsenic oxidizing bacteria (AsOB) has shown potential to effectively oxidize arsenite to arsenate without use of any chemicals. Arsenite is then effectively removed by adsorption or separation technologies. Iron Electrocoagulation (Fe-EC) is also emerging as an influential technique for arsenic removal that involves in-situ generation of iron coagulants using iron electrodes by electrolytic oxidation of anode. The main advantage of Fe-EC is that it does not require dosage of chemical coagulants so can be beneficial to communities with better access to electricity than chemicals.
This research work is done to combine the two techniques: biological oxidation of arsenite and Fe-EC, for better removal of arsenite from water. Batch studies on Fe-EC were performed in the laboratory to investigate the effects of charge dosage, charge dosage rate, initial arsenic concentration, arsenic oxidation state and different water matrices on the rate and extent of arsenic removal. Also, growth of AsOB on suitable bio-carrier was performed by continuous dosing of 150 μg/L arsenite-spiked water over a period of 49 days. The AsOB grown on the bio-carriers performed 90 % oxidation of 150 μg/L arsenite after a period of 35 days. Finally, two continuous flow system were developed one containing arsenite oxidation step by AsOB followed by Fe-EC and rapid sand filtration whereas the other contained only Fe-EC and rapid sand filtration. The system containing biological oxidation followed by Fe- EC removed arsenite below the WHO standard (10 μg/L ) from an initial arsenite concentration of 150 μg/L at a low iron dosage compared to the system where only Fe-EC was applied.