Dilution of seawater using dewatered construction water in a hybrid forward osmosis system

Abstract

In this study, dewatered construction water (DCW) was used for the first time as the feed solution (FS) in a combined pretreatment-FO process to dilute seawater (i.e. draw solution (DS)) for further desalination. It was found that at a FS and a DS flow rate of 2.2 L.min-1 gave the optimum membrane flux with minimal fouling effects. The addition of a spacer in the membrane feed side was effective at low flow rates (0.8 and 1.5 L.min-1). The FS was then pretreated using two methods: settling and multimedia filtration and run in the FO unit at a low flow rate of 0.8 L.min-1 using a spacer at the feed side. Results revealed a significant increase in the FO membrane flux by 64.3% when multimedia filtration was carried out with a low flux reduction of 7.7%. While the settling method achieved only 13.5% increase in permeate flux and 12.5% flux reduction over time. The multimedia filtration process removed most of the fouling particles and resulted in an elevated and more consistent membrane flux. Results also showed that the water flux was 1.3 times higher when the membrane's active layer was facing the draw solution than when it was facing the feed solution. Cost analysis showed that FO treatment of DCW was USD 7.88 day-1 and it was slightly cheaper when the FO operates on the PRO mode.

Unlocking the application potential of forward osmosis through integrated/hybrid process

“…Subsequently, the FO membrane was less exposed to the contaminants that could block its surface for water passage. A similar finding was also reported by Hawari et al (2018) where the FO membrane flux was approximately 50% higher when subjected to the concentration of pretreated dewatered construction water (through multimedia filtration) [137]. The significant increase in flux was due to the removal of large amounts of suspended solids and turbidity (impurities) by the multimedia filtration pretreatment process, reducing the turbidity and total suspended solids from 300 NTU and 325 ppm to 24 NTU and 21 ppm, respectively.…”

Synthesis and characterization of PVC‐TFC hollow fibers for forward osmosis application

“…FO membranes structure has a porous nonselective support layer and a selective (active) layer coating the support layer 17 . This nature of FO membranes leads to separate membrane orientation in two modes: FO mode and PRO mode 46 . In PRO mode, water moves from the feed solution to the draw solution to dilute the draw solution at the active TFC layer and then the concentration inside the support layer increased, which can cause concentrative ICP.…”

Organic Fouling in Forward Osmosis: A Comprehensive Review

“…An integrated forward osmosis system can treat dewatered construction water (DCW) for reuse or for discharging into the sea, which reduces the adverse impacts of DCW on the environment if discharged to the sea directly [62]. IV.…”

“…Cost-effective pre-treatment of wastewater can have numerous benefits such as disinfection, settling of large suspended particles, and removal of total suspended solids (TSS) as well as low fouling propensity of the feed wastewater after pre-treatment. Pre-treatment of wastewater includes but is not limited to using sand filters, settling and multimedia filters [62], and using Ultrasound and Ultraviolent (UV) treatment [125] coagulation-flocculation and flotation [126]. Employing cost-effective pre-treatment for high Total dissolved solids (TDS) solution can help reduce membrane fouling, protect the membrane, and improve Forward osmosis (FO) performance [127].…”

“…Employing cost-effective pre-treatment for high Total dissolved solids (TDS) solution can help reduce membrane fouling, protect the membrane, and improve Forward osmosis (FO) performance [127]. Settling and multimedia filtration has been proven as an excellent alternative for dilution of seawater in a hybrid FO system [62]. In the settling process, the settleable solids tend to settle down at the bottom due to a gravitational sedimentation mechanism.…”