Can a forward osmosis-reverse osmosis hybrid system achieve 90 % wastewater recovery and desalination energy below 1 kWh/m 3? A design and simulation study

The emergence of the forward osmosis (FO)-reverse osmosis (RO) hybrid offers simultaneous water reuse and desalination by incorporating FO for wastewater (WW) recovery to dilute seawater (SW) before undergoing RO treatment. The potential of osmotic dilution within the FO-RO hybrid promises elevated FO recovery rates and decreased specific energy consumption (SEC) of RO. Yet, pushing the system to its limits remained unexplored. Employing MATLAB (R) for simulations across various feed-to-draw volume ratios and diverse WW salinities, the study explored the feasibility of achieving enhanced FO recovery from WW. The study extended to evaluating the adaptability of existing desalination plants to process diluted SW using LewaPlus (R) design software. The FO simulation confirmed the feasibility of achieving 90 % WW recovery across various operational conditions in many instances. Yet, the optimal configuration for achieving both 90 % WW recovery and RO SEC below 1 kWh/ m 3 was specific: an 80:20 feed-to-draw volume ratio with an initial WW salinity of 0.5 g/l in FO. This resulted in reduced SW salinity (7.4 g/l), enabling RO desalination at 0.96 kWh/m 3 , showcasing potential retrofitting applications for existing desalination plants based on software design response. In the comparative study to determine the optimal approach for integrated water reuse and desalination between FO-RO hybrid and independent schemes, the energy efficiency of RO in independent schemes appears favorable, but FO-RO hybrid system may offer other benefits considering its double-dense barrier protection.