Economic evaluation of salt recovery from wastewater via membrane distillation-crystallization

Membrane crystallization is a promising method that could reduce the treatment costs of wastewater containing inorganic salts because of its easy functioning, its low energy consumption and the possible revalorization of the salts. However, very few economic evaluations have been conducted in this field of work, which makes the transition from laboratory scale to industrial levels difficult. This work addresses the economic analysis of crystallization of three inorganic salts i.e., sodium sulphate, sodium carbonate and potassium nitrate, using osmotic membrane contactors. Beforehand, the membrane area requirements are analysed because of their significant influence on process viability. Subsequently, the costs, salt sale profits and benefits are evaluated. The results show that the membrane area requirements are strongly dependent on the concentration of the osmotic agent used in the contactor. Furthermore, a sensitivity analysis showed that the economic viability of the process is significantly influenced by the market value of the salts to be crystallized, the plant availability, the membrane price and the overall mass transfer coefficient of the membrane, suggesting that recovery of high-value salts or intensified research dedicated to low-cost and high-performance membranes could lead to a process substantially more performant and cost-effective.