Modeling Approach to Estimate Energy Consumption of Reverse Osmosis and forward Osmosis Membrane Separation Processes for Seawater Desalination

Due to growing industrialization and population increase, water scarcity is becoming a major global concern. Desalination is often regarded as a potential solution to the worldwide water crisis; however, due to rising prices and energy usage, desalination has remained a research focus. Traditionally, specific energy consumption (SEC) kWh/m3 for seawater desalination has been calculated using a hybrid approach that ignores membrane design attributes and operational parameters. The current study constructed a mathematical framework based on well-established theory to quantify and compare the energy consumption of pressure-driven and osmotic-driven membrane separation processes by incorporating the necessary membrane design and operational parameters into the model framework. The model results were compared to the literature data and found to be in good agreement. The findings of this study show a non-linear relationship between the membrane flowrate factor and the energy needs of reverse osmosis RO, with the effect being more obvious at low values of Kf < 50 L/h.bar, where Kf is equal to the product of membrane permeability and membrane area. The results also showed that the lowest SEC was obtained at 60–65% recovery, and, from model testing, the energy consumption was 3.65 kWh/m3 and 3.88 kWh/m3 for the RO and FO–RO processes, respectively. Additionally, the hybrid process demands more membrane area, which further raises the cost of desalination. The mathematical framework developed in this work will act as a prediction design tool for membrane plant designers to check and compare the feasibility of these processes before experimental work to save money and time.