Forward osmosis to treat effluent of pulp and paper industry using urea draw-solute: Energy consumption, water flux, and solute flux

[Display omitted] •The effluent of the pulp & paper industry was treated by forward osmosis process.•Specific energy consumption (SEC) was lowest for fertilizer-based draw solution.•Low value of SEC obtained as 0.17 kWh/m3 in FO process using urea as draw solute.•Lower solute flux was observed for FO runs compared to RO and NF under same feed.•At higher draw solution concentration dradual increase of resistance was minimum. Wastewater treatment via suitable routes is necessary to protect the environment and fill the shortage of freshwater. An osmotic pressure-driven membrane separation process of forward Osmosis (FO) has gained attention as an alternative water treatment process over the conventional approaches. FO process needs a draw solution (DS). A commonly used fertilizer such as urea in water can be used as a DS, and after the FO run, diluted DS may use as fertilizer. Thus, it can simultaneously generate freshwater for agricultural purposes from industrial wastewater. FO process using thin-film composite flat sheet membrane has been investigated for various lab-made solutions and pulp & paper industrial effluent as feed solutions (FSs) under varying DSs of 0.25, 0.5, 1, and 2 M urea solutions. Limited FO studies examined the long-term and repetitive runs using the same membrane to access the fouling, water, and solute flux behavior with real industrial wastewater as feed solutions (FS). The long-term experimental results prove the strong influences of DS concentration on specific energy consumption (SEC), fouling behavior, and water flux. Increasing the cross-flow rate from 0.33 to 1 L/min has a minor effect on water flux, but SEC increases significantly from 0.17 ± 0.01 kWh/m3 to 0.50 ± 0.03 kWh/m3. FO runs show that the overall water flux enhances due to higher osmotic pressure difference and lesser membrane fouling at higher DS concentration using pulp & paper industrial secondary effluent as FS. This study demonstrates that a low-energy FO process can recover water from industrial wastewater while simultaneously produces a diluted fertilizer for fertigation.