NANOFILTRATION PRETREATMENT FOR SEAWATER REVERSE OSMOSIS: EXPERIMENTAL AND SIMULATION ASSESSMENT OF PERFORMANCE AND ENERGY DISTRIBUTION

Abstract

This thesis investigates nanofiltration (NF) as an alternative pretreatment to ultrafiltration (UF) in seawater reverse osmosis (SWRO) desalination systems through an integrated experimental and simulation-based framework grounded in real Arabian Gulf seawater and validated against operational data from an existing full-scale SWRO plant. Unlike conventional evaluations that rely on overall specific energy consumption (SEC) as the primary performance metric, this study adopts a unit-wise energy breakdown approach alongside thermodynamic scaling assessment and multi-configuration process modeling, providing a more rigorous and industrially relevant basis for system-level comparison. Four NF membranes (1 kDa to 200 Da) were evaluated alongside a UF benchmark (150 kDa) for ion rejection, flux, fouling resistance, and hydraulic behavior. Scaling was assessed using both Langelier Saturation Index (LSI) and thermodynamic indices via PHREEQC with the Pitzer model. Results showed LSI overestimates scaling under high-salinity conditions, confirming the need for activity-based modeling. NF45 achieved the highest rejection of Ca²⁺ (~60%), Mg²⁺ (~88%), and SO₄²⁻ (~98%), significantly reducing scaling potential for key minerals. Membrane tightness alone did not predict fouling resistance, highlighting the role of morphology. NF pretreatment was found to redistribute rather than eliminate scaling, stabilizing RO feed while concentrating scale-forming species in the retentate. Experimental NF45 data were integrated into simulations using DuPont WAVE™ and EES to compare a UF–RO baseline with three NF–RO configurations. All cases were evaluated under identical conditions. NF reduced RO feed osmotic pressure, lowering operating pressure from ~68 bar to 43.8 bar and decreasing RO energy consumption from 2.55 to 1.59 kWh·m⁻³ (~47% reduction in pump power). However, the NF stage introduced higher upstream energy demand, resulting in greater overall system energy compared to UF–RO. Retentate pressure recovery reduced total energy by ~7.23%, demonstrating the importance of system integration.

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