Synergistic mitigation of membrane scaling via arginine-based surface and phytic acid cleaning in autonomous forward osmosis process

The concept of a single FO process using an ammonium bicarbonate draw solution was proposed to leverage its low energy requirement (0.24 kWh/m 3 ) and high fouling resistance in desalination and water treatment, as pure water can be easily separated by heating to below 60 °C. However, the water production of this single FO process rapidly declined due to membrane scaling, primarily caused by the reverse solute diffusion of carbonate ions reacting with divalent ions in the feed solution. In this study, we utilized arginine and phytic acid—both environmentally friendly substances—for membrane modification and cleaning, respectively, to enhance the feasibility of the single FO process by reducing membrane scaling. Membrane modification with arginine led to a significant decrease in the flux decline ratio (FDR) from 40.06% in the virgin state to 7.46% after optimization with a 7.5% arginine concentration and a 30-min reaction time. Additionally, the calcium content on the membrane surface was reduced from 32.49% to 0.96%, and the deposited calcium mass decreased from 1140.85 to 764.45 mg-Ca/m 2 . Arginine modification altered the membrane surface properties, including surface charge and zwitterionic characteristics, thereby mitigating membrane scaling, allowing the initial cleaning time in the single FO process to be extended from 1.5 to 10.0 h. Furthermore, phytic acid enhanced the limited efficiency of conventional cleaning methods, improving water flux from 37% to 80% due to its acidifying and chelating properties. This strategy improved the operational stability of the autonomous FO process by mitigating membrane scaling and extending the cleaning interval under the investigated operating conditions.