SUSTAINABLE BRINE TREATMENT VIA PHOTO-ELECTRODIALYSIS: FROM PHOTOELECTRODE OPTIMIZATION TO LIFE CYCLE ASSESSMENT OF INTEGRATED SYSTEMS

Abstract

Sustainable brine management remains a critical challenge in desalination-dependent regions, where hypersaline reject streams pose ecological risks while containing valuable resources. This thesis investigates photo-electrodialysis (PED) as an innovative technology, integrating photoactive electrodes with electrodialysis (ED) to enable simultaneous ion separation and nutrient recovery. TiO2 thin-film photoelectrodes were fabricated on fluorine-doped tin oxide (FTO) glass substrates using ultrasonic spray pyrolysis (USP). Two morphologies, S1-patterned and S2-plain, were prepared and characterized via scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The analyses confirmed nanostructured, mixed anatase-rutile TiO2 phases and heterogeneous agglomerated morphology. Electrochemical performance was evaluated in a custom PED cell using 0.5 M NaOH electrolyte under solar simulator illumination. The S1-patterned demonstrated superior photoelectrochemical behavior, delivering higher and stable photocurrent (up to 8 μA at 0.4 V and 17 μA at 0.6 V; corresponding to photocurrent density of 0.133 μA cm⁻2 and 0.283 μA cm⁻2, respectively) and 70 mV photovoltage, improved charge transport and reduced recombination losses compared to the S2-plain. Additionally, two cradle-to-gate life cycle assessments (LCA) were conducted using the CML 2001 methodology in GaBi software. The first assessed an integrated NF-RO-PED system supplying nutrient-rich water to a hydroponic greenhouse to produce 1 tonne of tomatoes. The global warming potential (GWP) was calculated as 1.39 kg CO2 eq. kg⁻1 tomatoes under Qatar’s fossil-dominated grid, with electricity consumption and PED materials identified as the primary environmental hotspots. Switching to solar or wind electricity reduced GWP by 86-88%. The second LCA evaluated a multi-stage brine valorization system (NF-RO-UHP-RO-chemical precipitation-potassium exchange-bipolar membrane ED-evaporation) for sodium hydroxide (NaOH) production, yielding a GWP of 2.121 kg CO2 eq. kg⁻1 NaOH. Electricity demand and stainless steel or membrane fabrication dominated the impacts; renewable electricity integration could lower GWP by 80-90%. This work demonstrates that optimized PED photoelectrodes integrated with membrane processes offer a technically feasible and environmentally competitive pathway for transforming brine into valuable resources, while reinforcing circular economy principles in water-scarce regions and underscoring the pivotal role of renewable energy in low-carbon brine valorization.

Date of Award	2026
Original language	American English
Awarding Institution	HBKU College of Science and Engineering