Efficiently Combining Water Reuse and Desalination through Forward Osmosis—Reverse Osmosis (FO-RO) Hybrids: A Critical Review

Abstract

Forward osmosis (FO) is a promising membrane technology to combine seawater desalination and water reuse. More specifically, in a FO-reverse osmosis (RO) hybrid process, high quality water recovered from the wastewater stream is used to dilute seawater before RO treatment. As such, lower desalination energy needs and/or water augmentation can be obtained while delivering safe water for direct potable reuse thanks to the double dense membrane barrier protection. Typically, FO-RO hybrid can be a credible alternative to new desalination facilities or to implementation of stand-alone water reuse schemes. However, apart from the societal (public perception of water reuse for potable application) and water management challenges (proximity of wastewater and desalination plants), FO-RO hybrid has to overcome technical limitation such as low FO permeation flux to become economically attractive. Recent developments (i.e., improved FO membranes, use of pressure assisted osmosis, PAO) demonstrated significant improvement in water flux. However, flux improvement is associated with drawbacks, such as increased fouling behaviour, lower rejection of trace organic compounds (TrOCs) in PAO operation, and limitation in FO membrane mechanical resistance, which need to be better considered. To support successful implementation of FO-RO hybrid in the industry, further work is required regarding up-scaling to apprehend full-scale challenges in term of mass transfer limitation, pressure drop, fouling and cleaning strategies on a module scale. In addition, refined economics assessment is expected to integrate fouling and other maintenance costs/savings of the FO/PAO-RO hybrid systems, as well as cost savings from any treatment step avoided in the water recycling.

Practical considerations for operability of an 8″ spiral wound forward osmosis module: Hydrodynamics, fouling behaviour and cleaning strategy

“…The improvements include higher water permeability, greater selectivity and rejection, smoother active layer surface allowing lower fouling propensity, and quite importantly, a specifically adapted porous support layer offering low internal concentration polarisation (ICP) yet still appropriate mechanical support for practical operation [4,5]. The first commercially available and specifically tailored FO membranes, based on cellulose triacetate (CTA), were developed by Hydration Technology Innovations (HTI, Albany, OR), and have been examined in various applications by numerous research groups [8][9][10][11][12][13]. More recently, thin film composite (TFC) FO membranes were designed with a polyamide selective layer, and these feature higher water flux and better solute rejection compared to CTA membranes [14][15][16][17].…”

Reverse osmosis pretreatment technologies and future trends: A comprehensive review

“…Pretreatment helps in altering the sea water characteristics and improve SWRO performance by providing the constant feed water quality required for efficient RO plant operation. To date, are utilized, depending upon the incoming feed water quality [27,28]. Figure 4 is a schematic of such a hybrid system, while Table 1 highlights common seawater quality parameters that are essential to investigate before concluding on the selection of pretreatment required.…”

Critical flux-based membrane fouling control of forward osmosis: Behavior, sustainability, and reversibility

“…Hybrid FO processes have recently emerged as possible systems for the simultaneous treatment of impaired/reclaimed water and seawater for reuse [2] [3] [4] [5] since standalone FO process cannot economically achieve either water treatment or desalination of seawater. These hybrid processes can bring many advantages regarding the energy consumption and the water quality: i) decrease of desalinated energy cost because seawater is diluted before entering RO desalination, ii) reduction of the fouling propensity of the RO stage through pretreatment of impaired water; (iii) a multibarrier protection is established to improve contaminant removal; thereby giving opportunity for safe and high-quality reuse of impaired water [5] [6] [7]. In detail, complex wastewater (i.e., raw sewage, primary effluent, secondary effluent, biologically treated wastewater effluent) can be directly pre-treated by FO process (i.e., pre-treated wastewater or pre-concentrated wastewater) and subsequently potable water can be produced by combining with a draw solute recovery process (i.e., reverse osmosis or membrane distillation) [8] [9].…”