Liquid Biphasic Systems: Principles and Potential for Wastewater Treatment

Water is one of the most vital natural resources, essential to all forms of life. As demand increases and pollution from domestic, industrial, and agricultural sources continues to grow, wastewater treatment has become an urgent challenge that must be addressed. Therefore, the investment in novel techniques useful for the treatment and purification of this resource is of utmost importance. Liquid Biphasic Systems (LBSs) are a simple, biocompatible, and easily scalable liquid–liquid extraction technique which has shown significant potential for the recovery of target compounds, such as antipyretics and antibiotics, from water, enabling its purification. In this study, two new LBSs composed of three biodegradable, low-toxicity solvents were investigated: {ethyl acetate (1) + propan-1-ol or ethyl lactate (2) + water (3)}, at 298.15 K and 0.1 MPa. The second component in each system is miscible with ethyl acetate while being largely immiscible with water, allowing for the formation of two distinct liquid phases. The systems were characterised by determining the solubility curves using the cloud-point method and calculating the composition of 6 tie-lines through third-degree polynomial correlations of liquid density and refractive index. The tie-line lengths ranged from 41 to 77 % in mass for the propan‑1‑ol system and from 47 to 103 % in mass for the ethyl lactate system. Moreover, the experimental tie-line data were successfully correlated using the Othmer–Tobias and Bancroft–Hubard models, with both systems yielding coefficients of determination (R²) greater than 0.985 for both models. The experimental liquid–liquid equilibria (LLE) data were then effectively described using the UNIversal QUAsi-Chemical (UNIQUAC) model, with standard deviations (σ) lower than 10^-3 being obtained for both systems. This work offers valuable insights into the phase separation behaviour of two new LBSs, contributing to the advancement of greener and more efficient extraction techniques for sustainable wastewater purification.