| dc.description.abstract | This thesis presents an investigation into the modelling of forward osmosis (FO) driven reverse osmosis (RO) desalination system evaluating various approaches and their performance under different operating scenarios. It also examines the potential of using Pressure Retarded Osmosis (PRO) as a renewable energy source for powering FO-RO systems. The FO process is modelled and developed in terms of key operating parameters with a focus on optimising system performance to understand the impact on water flux (Jw) and achieve the minimum specific energy consumption (SEC). The development process is conducted based on different salinity gradients, employing a Cellulose Triacetate (CTA) flat sheet membrane, which is commonly used due to its versatility and availability in modelling FO process. It facilitates exploration of emerging technologies such as FO and PRO allowing for easy comparison with existing studies, ensuring consistent evaluations across varied salinity gradients. The study revealed enhanced permeate rates with increased draw solution concentration, achieving optimal water flux with a concentrated NaCl solution. It highlighted the balance needed between increasing osmotic pressure for efficiency and mitigating risks like concentration polarisation. The recommended operational approach emphasises optimising draw solution concentration to enhance water flux while minimising energy consumption and polarisation concentration effects. In FO-RO system, the overall performance, including regeneration processes, is evaluated. Integrating FO as a pre-treatment step enhances efficiency and durability by reducing membrane scaling and energy consumption within the desalination system. This approach effectively minimises RO fouling and maintains water flux, leading to lower overall desalination energy requirements. The study confirms that FO pre-treatment can significantly reduce energy consumption, particularly with varying feed water qualities and salinities. The study compares FO-RO systems with traditional RO, revealing the FO-RO system, especially at 1M NaCl, to be more energy efficient against traditional RO setups for feed salinities between 35 to 45 g/L. However, it notes a potential efficiency constraint at higher draw concentrations due to the RO step's pressure handling capacity, highlighting a balance between energy savings and operational feasibility. For investigating the use of a PRO process to power an FO-RO system, the study focused on optimising key operational parameters to maximise PRO system power output. By adjusting salinity gradients and maintaining consistent CTA membrane characteristics, it was found that increasing the draw to feed flow rate ratio enhanced power density, primarily through minimising concentration polarisation and enhancing water flux. Moreover, higher TDS levels in the RO brine further improved power density. While the power produced by the PRO process fell short of fully powering the FO-RO system, it nonetheless contributed a substantial portion of the required energy. | en_US |
