Alleviation of water flux decline in osmotic dilution by concentration-dependent hydraulic pressurization

- Additional hydraulic pressure is proposed to compensate water flux loss in OD.
- ICP determines the availability of HP method at both membrane orientations.
- Water flux decline can be mitigated by constant pressure under limited conditions.
- CDHP is relevant to variational concentration difference in HP processes.
- 3-Stage HP leads to 12.79% increase in final water flux at AL-FS orientation.

Forward osmosis has motivated practical applications in seawater desalination and agricultural irrigation due to its potential advantage of osmotic dilution. However, water flux decline accompanies with continuous dilution of the DS, which will cause extra membrane expenditure, until final osmotic equilibrium. Without the help of additional driving force, it is impossible to reduce driving force loss in OD. In this study, concentration-dependent hydraulic pressure is exactly introduced as an auxiliary driving force. Investigations on water flux decline behavior in OD showed that water fluxes at lower initial concentration difference, lower initial solution volume and AL-DS orientation suffered more severe decline; furthermore, it implied that additional hydraulic pressure could alleviate adverse effects of greater concentration difference variation generated by pressure-induced water flux increment on water flux. For given dilution of the DS, minimized change in bulk FS concentration was conducive to ensure the effectiveness of constant hydraulic pressure on reducing water flux decline. Validation experiments demonstrated that current model equations were more appropriate under lower hydraulic pressures, and stable water flux also relied on concentration difference variation corresponding to applied hydraulic pressure. Potential implications were highlighted in the context of technical progress of membrane preparation and application potential of OD.

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