Effect of fo spacer, membrane properties and fouling on the specific energy consumption of hybrid fo-ro desalination system / Goi Yi Ken

Faculty of Chemical and Process Engineering Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang Al Sultan Abdullah - 2025

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Forward osmosis (FO) is a membrane process that utilizes osmotic pressure for water transport. FO is increasingly gaining interest as a pretreatment for reverse osmosis (RO) in hybrid FO-RO systems due to advantages such as reduced pretreatment energy consumption, enhanced contaminant removal, and improved water quality. However, fully optimizing their large-scale performance remains challenging due to insufficient studies on spacers, advanced membranes, temperature effects, and fouling under large-scale conditions. This main objective of this work is to study the effect of FO spacer, membrane properties and fouling on the specific energy consumption of hybrid FO-RO desalination system. First, this study assessed the impact of a hypothetical advanced spacer, modelled with a 50% higher Sherwood number compared to conventional spacers, on water flux, specific energy consumption (SEC), and concentration polarization (CP). The results demonstrate that this advanced spacer can reduce SEC by up to 9.17% at a 40% recovery rate, primarily by mitigating external concentration polarization (ECP). Sensitivity analysis further highlighted Sherwood (Sh) correlation coefficients as the most critical factor influencing SEC. Second, this study investigates the impacts of temperature and FO membrane properties (A, B, and Ss) on CP and SEC. This study explored a wide range of membrane parameters, with lower limits set by conventional membranes and upper limits reflecting the most advanced lab-scale membranes currently available. Similarly, operating temperatures ranged from a lower limit representing winter conditions to an upper limit of 40°C, beyond which membrane degradation can occur. Within these ranges, results showed that reducing Ss by a factor of 10 enhanced FO recovery by 177.6% and decreased SEC by 36.6%. Conversely, increasing A beyond 3 LMH bar⁻¹ demonstrated diminishing returns due to rising ECP and ICP. Furthermore, elevating operating temperatures from 10°C to 40°C consistently reduced SEC by 14.3%. Lastly, this work developed a time-dependent fouling model specifically for FO spiral-wound membrane (SWM) systems to assess fouling's impact in large-scale FO operations. This model showed strong agreement with experimental data, with a Mean Absolute Percentage Error (MAPE) of 9.43%. Main findings indicate that feed flow rate is the most influential parameter for effective fouling control. In conclusion, this simulation work demonstrates that integrating advanced FO spacers, optimizing membrane properties, and elevating operating temperatures can significantly enhance the efficiency of large-scale hybrid FO-RO desalination systems. The developed modeling framework serves as a valuable tool for predicting fouling in FO SWM systems.