Abstract
During reverse osmosis (RO) membrane filtration, performance is dramatically affected by fouling, which concurrently decreases the permeate flux while increasing the energy required to operate the system. Comprehensive design and optimization of RO systems are best served by an understanding of the coupling between membrane shape, local flow field, and fouling; however, current studies focus exclusively on simplified steady-state models that ignore the dynamic coupling between fluid flow, solute transport, and foulant accumulation. We developed a customized solver (SUMs: Stanford University Membrane Solver) under the open source finite volume simulator OpenFOAM to solve transient Navier–Stokes, advection–diffusion, and adsorption–desorption equations for foulant accumulation. We implemented two permeate flux reduction models at the membrane boundary: the resistance-in-series (RIS) model and the effective-pressure-drop (EPD) model. The two models were validated against filtration experiments by comparing the equilibrium flux, pressure drop, and fouling pattern on the membrane. Both models not only predict macroscopic quantities (e.g., permeate flux and pressure drop) but also the fouling pattern developed on the membrane, with a good match with experimental results. Furthermore, the models capture the temporal evolution of foulant accumulation and its coupling with flux reduction.
Highlights
Reverse osmosis (RO) filtration systems are widely applied in seawater desalination [1,2,3,4,5], landfill leachate treatment [6,7], and wastewater reclamation [8,9,10,11,12,13,14]
In addition to the parameters listed above, which are shared by both the RIS and EPD models, each model has one undetermined parameter: Ak in the RIS model, and Ap in the EPD model. Such parameters are fitted from experimental flux measurements on the benchmark rectangular geometry, R1, and kept constant to predict flux, pressure, and fouling pattern for the all other geometries with Ak = 0.067 and Ap = 3600, for the RIS and EPD models, respectively
We investigate the ability of two different fouling models (RIS and EPD) to correctly capture both system-scale performance quantities, namely permeate flux and pressure drop, as well as fine-scale features, such as high fouling regions
Summary
Reverse osmosis (RO) filtration systems are widely applied in seawater desalination [1,2,3,4,5], landfill leachate treatment [6,7], and wastewater reclamation [8,9,10,11,12,13,14]. Ling and Battiato [46] developed a model that couples the transient Navier– Stokes and the advection–diffusion equations, as well as an adsorption–desorption equation for foulant accumulation They validate it against experimental data and demonstrate that it is able to correctly capture unsteady measurements of permeate flux, its capability of correctly capturing spatial distribution of the foulant in morphologically complex membranes was not evaluated. The model is validated by comparing three-dimensional simulations with fouling experiments conducted by Xie and et al [44], who measured (i) the permeate flux and pressure drop and (ii) the spatial distribution of fouling patterns for different spacer configurations Such comparisons demonstrate the RIS and EPD models’ capability of capturing both system-scale quantities (i.e., flux and pressure) and local effects (fouling pattern).
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