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Optimization of Reverse Osmosis Concentration for High-Salinity Iron Phosphate Wastewater

  • Xifeng Yan 1,2,   
  • Suhang Kong 1,   
  • Mi Deng 3,   
  • Haofei Chen 1,   
  • Yong Wang 4,*

Received: 13 Mar 2026 | Revised: 30 Apr 2026 | Accepted: 02 Jun 2026 | Published: 23 Jun 2026

Abstract

This study investigates reverse osmosis (RO) concentration for high-salinity iron phosphate wastewater, with emphasis on osmotic pressure behavior, water permeability, concentration enhancement, and fouling control. The measured osmotic pressure increased markedly with total dissolved solids (TDS) and deviated by 18–25% from the ideal van’t Hoff prediction at high ionic strength. A temperature-corrected osmotic-pressure model (R2 = 0.987) and a ternary quadratic permeability-coefficient model (R2 = 0.99) were established. The water permeability coefficient ranged from 3.7 to 12.0 L·MPa−1·m−2·h−1. To extend the RO concentration limit, an RO5+RO7 staged configuration was proposed. In this study, the term “micro-osmosis membrane process” is used specifically for a two-stage RO configuration in which a high-rejection RO5 element is followed by a lower-rejection RO7 element. Unlike conventional staged RO using the same high-rejection membrane in both stages, the RO7 element deliberately permits limited salt passage to the permeate side, thereby lowering the effective osmotic-pressure difference across the second-stage membrane without adding an external draw solution. Compared with the conventional RO5+RO5 configuration, this design increased the concentration endpoint by 8.4%. Membrane autopsy by SEM-EDS indicated that the dominant fouling was Fe-Mn-Ca composite scaling. A targeted two-step cleaning strategy, consisting of 1% tetrasodium EDTA + 0.5% ammonia water + 0.1% sodium hexametaphosphate alkaline cleaning followed by 2% citric acid acid washing, restored the flux recovery rate to >94% and salt rejection to 99.7%. These results provide a practical RO concentration and cleaning strategy for high-salinity iron phosphate wastewater treatment.

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Yan, X.; Kong, S.; Deng, M.; Chen, H.; Wang, Y. Optimization of Reverse Osmosis Concentration for High-Salinity Iron Phosphate Wastewater. Membrane Horizons 2026, 1 (1), 3.
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