Modeling and experimental investigation of factors responsible for maximizing the betanin concentration by spiral-wound FO module using Na2SO4-based draw solution

Abstract

The conventional process for concentrating betanin from beetroot juice is expensive due to the requirement of solvents and high energy consumption. However, concentrating betanin using a forward osmosis (FO) process offers a cost-effective alternative without phase change. This modeling and experimental study investigated the most significant factors responsible for enriching the feed side betanin concentration by the FO process using a Na₂SO₄-based draw solution. The module-scale FO transport model parameters were estimated and validated by performing the lab-scale experiments. Furthermore, the FO model is simulated to explore the influence of the process operating variables, draw solution temperature, and the active membrane area to maximize the betanin concentration in the outlet process stream. The results show that the inlet draw flow rate significantly enhances the betanin concentration in the outlet feed stream. Furthermore, simulations investigate the FO membrane parameter (solvent permeability) and its influence on enriching the feed side betanin concentration inside the feed stream. The simulated results show that maintaining the same operating conditions, an increase in water permeability (1.22 ×10⁻¹² to 5.5 ×10⁻¹¹m/Pa.s) concentrates 66.6 % betanin inside the feed stream more compared to the inlet draw flow rate at 25 L/h. In contrast, variations in solute permeability have a negligible impact on the increase in betanin concentration. Finally, the study concludes that the water permeability and inlet draw flow rate were the most significant factors responsible for enriching the feed side betanin or any other organic compound using FO membrane.