Modelling of arsenic (III) removal from aqueous solution using film theory combined Spiegler-Kedem model: pilot-scale study

Arsenic contamination in drinking water is recognized as major health hazard worldwide. As reported in literature, more than 19% Indians are consuming lethal levels of arsenic for drinking purposes. In this work, arsenic (III) removal was studied using HFN300 polyethersulfone nanofiltration membrane in spiral wound configuration. Various membrane parameters such as hydraulic permeability (4.87 L m⁻² h⁻¹ bar⁻¹), mass transfer coefficient (0.957*10⁻⁶ m s⁻¹), reflection coefficient (0.9), and solute permeability (2*10⁻⁹ m s⁻¹) were estimated using film theory combined Spiegler-Kedem (FTCSK) model. The higher value of reflection coefficient suggested the impervious nature of nanofiltration (NF) membrane used for arsenic (III) solute rejection. The influence of various operating parameters such as transmembrane pressure, initial feed concentration, and feed flowrate on membrane performance was also examined. It was found that arsenic (III) rejection was dependent on pressure and feed concentration. Result showed that more than 96.4% arsenic (III) rejection was achieved for 50 mg L⁻¹ of feed at optimized conditions. As HFN300 membrane was negatively charged at pH 8 and arsenic (III) was available in neutral solute form, electro-migration was not considered for solute rejection mechanism. Solution diffusion with significant coupling between solute and solvent, steric hindrance effect, convection, and solute-membrane affinity interactions were considered dominant factors for the possible solute rejection mechanism. Rejection efficiency (% R) and permeate flowrate (Q₂) were simulated and compared with experimental results. It was found that simulated results were in excellent agreement with the experimental results. The maximum error obtained was within 10% for both % R and Q₂. This confirms the efficacy of FTCSK model in predicting arsenic (III) removal using NF membrane. The annualized cost per cubic metre of treated water was estimated as 3.32 $/m³. This further confirms the feasibility of using NF process in removing arsenic from contaminated water.