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ABSTRACT
A pilot-scale reverse osmosis (RO) followed behind a membrane bioreactor (MBR) was developed for the desalination to reuse wastewater in a PVC production site. The solution–diffusion–film model (SDFM) based on the solution–diffusion model (SDM) and the film theory was proposed to describe rejections of electrolyte mixtures in the MBR effluent which consists of dominant ions (Na+ and Cl−) and several trace ions (Ca2+, Mg2+, K+ and SO42−). The universal global optimisation method was used to estimate the ion permeability coefficients (B) and mass transfer coefficients (K) in SDFM. Then, the membrane performance was evaluated based on the estimated parameters which demonstrated that the theoretical simulations were in line with the experimental results for the dominant ions. Moreover, an energy analysis model with the consideration of limitation imposed by the thermodynamic restriction was proposed to analyse the specific energy consumption of the pilot-scale RO system in various scenarios.
Symbols and abbreviations
| A | = | Water permeability coefficient (m3 m−2 h−1 kPa−1) |
| a | = | The membrane area (m2) |
| B | = | Solute permeability coefficient (m3 m−2 h−1 kPa−1) |
| Cf | = | Salt concentration in feed stream (mg L−1) |
| Cm | = | Solute concentrations at retentate side of membrane (mol L−1) |
| Cp | = | Solute concentrations in the permeate (mol L−1) |
| Cr | = | Salt concentration in retentate stream (mg L−1) |
| E | = | Net energy required for cross-flow RO (J) |
| Ep | = | Energy required for permeate production (J) |
| Er | = | Energy remaining in retentate stream (J) |
| foc | = | Osmotic pressure coefficient (Pa L mg−1) |
| i | = | Number of dissolved solute, i.e., ions and non-electrolyte solute (—) |
| Jw | = | Water volumetric flux (m3 m−2 h−1) |
| K | = | The mass transfer coefficient (µm s−1) |
| Mf,i | = | Molar concentration in the feed stream (mol L−1) |
| Mp,i | = | Molar concentration in the permeate (mol L−1) |
| ΔMs,i | = | Dissolved solute molar concentration difference (mol L−1) |
| P | = | Operation pressure (Pa) |
| Δp | = | Transmembrane pressure (kPa) |
| Qp | = | Product water (permeate) flow rate (m3 h−1) |
| Rg | = | The gas constant (8.31 kPa L K−1 mol−1) |
| Ro | = | Observed rejection (%) |
| Rr | = | Real rejection (%) |
| SEC | = | Special energy requirement (kWh m−3) |
| T | = | Temperature (K) |
| Vf | = | Feed water volume (m3) |
| Y | = | RO recovery (%) |
| Δπ | = | The osmotic pressure gradient (kPa) |
| = | The osmotic pressure of feed stream (Pa) |
Acknowledgements
The authors wish to thank Thomas Track and Christina Jungfer from DECHEMA for coordinating and organising project conferences. The authors also wish to thank Dr. Jens Alex for SIMBA® software supply and technical support at ifak – Institut fuer Automation und Kommunikation e.V.
Funding
The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007–2013) under the Grant Agreement No. 280756. The author Kang Hu thanks the financial support from China Scholarship Council (CSC No. 201206150055).