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.

Recently, the use of atomic layer deposition (ALD) technique for depositing thin films of metal oxides on membrane substrates has proved to be an effective way to fabricate commercially available UF or NF membranes to get tight UF/NF ceramic membranes. The main advantage of this technique is controlled deposition of a monolayer of metal oxides. This project was done to study the effect of ALD on 0.5 m long tubular membranes. TiO2 was deposited on the membranes by means of atmospheric pressure atomic layer deposition (APALD). This is different from most of the reported studies that use vacuum-based ALD. TiCl4 and H2O were used as the main precursors for depositing TiO2 through 2, 3 or 4 cycles of APALD. The growth rate of the deposited layer per cycle under different experimental conditions was measured indirectly using silicon wafers through ellipsometry. The effect of ALD was determined by measuring the membrane permeability and molecular weight cut-off (MWCO) values of the membranes before and after coating. The results obtained showed a variation in growth rate per cycle (GPC) of the deposited layers for different experimental conditions. APALD was performed on 6 membranes and the GPC rate was acceptable for only 2 membranes (0.14 nm/cycle and 0.03 nm/cycle), whereas the GPC for the other membranes was very high (more than 1 nm/cycle). After deposition, the 2 membranes with acceptable GPC rate showed a decrease in MWCO value by 627 Da and 405 Da respectively. These results demonstrated that APALD could be used to fabricate ceramic membranes, but only at proper experimental conditions for TiO2 deposition. An improved Carman-Kozeny model was also developed based on the MWCO value and on the GPC value, in order to predict the porosity and the permeability of the membranes. The results of the model and the measured permeability were compared; for some membranes, the model predicted correctly the permeability after coating.