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A NOVEL ASSISTED REVERSE OSMOSIS STRATEGY FOR TERTIARY POLISHING OF TREATED SEWAGE EFFLUENT WITH ENHANCED ENERGY EFFICIENCY
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Date
2026-06
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Kenan Alkhamri_ OGS Approved Thesis.pdf
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Abstract
In this study, a nanofiltration-assisted reverse osmosis (NF-ARO) strategy was investigated to reduce energy consumption and improve the long-term performance of reverse osmosis (RO) for tertiary-treated sewage effluent (TSE) reclamation. A hybrid RO operational approach was proposed, using Direct-RO (DRO) during the initial cycles and Assisted-RO (ARO) in later cycles, while maintaining high final permeate quality. TSE was first pretreated using nanofiltration, and the resulting NF permeate was used as feed for the RO process. During Cycles 1 and 2, ARO and DRO showed comparable average flux, similar dominant fouling behavior, mainly standard pore blocking, and close energy performance, with DRO showing a slight advantage. In Cycle 3, the benefits of NF pretreatment became more evident, as ARO achieved an 11.4% higher average flux and reduced specific energy consumption by up to 19% compared with DRO. These improvements were attributed to the reduction of fouling load, scaling precursors, suspended species, divalent ions, heavy metals, and organic contaminants reaching the RO membrane, leading to slower flux decline, improved flux recovery after cleaning, and lower irreversible fouling. Fouling analysis using Hermia’s models and membrane washing behavior indicated that NF pretreatment promoted more reversible fouling and improved cleaning efficiency between cycles. Based on these findings, the hybrid strategy of applying DRO during the first two cycles followed by ARO from Cycle 3 onward provided the lowest overall energy demand while maintaining stable flux performance and producing higher-quality permeate. The treated water complied with the Food and Agriculture Organization (FAO) water quality guidelines, confirming its suitability for irrigation. Overall, NF-assisted RO improves long-term operational stability, reduces irreversible fouling, and is expected to extend RO membrane lifespan, supporting its use as a sustainable strategy for long-term TSE reclamation.