Modeling organic fouling of reverse osmosis membrane: From adsorption to fouling layer formation

• Adsorption/fouling-layer model analyzes the flux decline during RO filtration. • The model provided a qualitative appreciation of the flux decline. • The factors of filtration time and membrane flux are considered in the fouling model. • The main interfacial interaction in each fouling step was discussed.

The combined model presented and discussed in this paper provides a more complete and rigorous description of the fouling behavior. The Table 4 Contact angle of the membrane surface based on adsorption/cake-formation model. Contact angle (°) Virgin EX1 Fig. 5. FTIR spectra of the membranes. The membrane was fouled by EX1. Transition point Fouling end 24.6 24.6 EX2 EX3 EX4 EX5 EX6 EX7 EX8 EX9 68.3 63.5 62.4 67.7 59.5 60.3 65.1 66.3 61.7 70.5 64.8 63.7 69.3 61.2 62.3 67.3 68.7 63.4 initial flux decline arises from the decrease in the available area for membrane filtration due to adsorption of the organic foulants on the membrane surface. The model also explicitly accounts for the formation of a fouling layer which offers the greatest total hydraulic resistance to filtration. The model provides a smooth transition from adsorption to fouling layer formation over the course of filtration studied. The experimental results of the transition time t1 are in very good agreement with the model calculation, demonstrating the validity of this approach to describing the flux decline during RO filtration of wastewater. It was evidenced by experiments that the initial stage of flux decline is attributed to the increase in hydrophobicity of the membrane. The later stage flux decline is controlled by the synergetic effect of the hydraulic resistance and the hydrophobicity of the fouling layer. Acknowledgments This work was supported by National Natural Science Foundation of China under the grant number of 21506222. Nomenclature J permeation flux (μm·s−1) t permeation measuring time (min) r initial fouling rate (μm·s−1·min−1) k initial fouling rate constant (μm·s−1·min−1) K Langmuir adsorption coefficient (L·mg−1) C concentration (mg·L−1) V volume (L) ka coefficients defined in Eq. (4) (μm·s−1·mg−1) kc layer fouling rate constant (min·m−4) A0 the active membrane area (m2) a, b, c coefficients defined in Eq. (16) Q, R coefficients defined in Eq. (17) Greek letters θ the number of occupied sites on the membrane surface α, β coefficients defined in Eq. (16) γ coefficients defined in Eq. (17)