This paper was focused on the investigation of a forward osmosis- (FO-) reverse osmosis (RO) hybrid process to cotreat seawater and impaired water from steel industry. By using this hybrid process, seawater can be diluted before desalination, hence reducing the energy cost of desalination, and simultaneously contaminants present in the impaired water are prevented from migrating into the product water through the FO and RO membranes. The main objective of this work was to investigate on pilot-scale system the performance of the combined FO pretreatment and RO desalination hybrid system and specifically its effects on membrane fouling and overall solute rejection. Firstly, optimization of the pilot-scale FO process to obtain the most suitable and stable operating conditions for practical application was investigated. Secondly, pilot-scale RO process performance as a posttreatment to FO process was evaluated in terms of water flux and rejection. The results indicated that the salinity of seawater reduced from 35000 to 13000 mg/L after 3 hrs using FO system, while after 6 hrs it approached 10000 mg/L. Finally, FO/RO system was tested on continuous operation for 15 hrs and it was demonstrated that no pollutant was detected neither in draw solution nor in RO permeate after the end of operating time.
a b s t r a c tForward osmosis (FO) hybrid systems have been developed recently as an alternative to conventional high-pressure membrane processes (reverse osmosis (RO)) for seawater desalination and wastewater treatment and recovery. However, the technical economic comparison with the RO processes for seawater desalination has not been clearly studied. The main objective of this investigation is to evaluate the detailed technical and economical feasibilities of the forward/reverse osmosis hybrid process for saline water desalination. The achievement of this study was conducted with the development of an economic model to calculate the effect of osmotic dilution of seawater feed stream on membrane area. A process design for hybrid FO/RO system for the simultaneous treatment of impaired and saline water with a pre-determined capacity, including material balance calculations, equipment sizing and selection were represented in this paper. Preliminary economic studies of the proposed systems for selected two cases were under taken: Ezz Steel Company treated wastewater with seawater, and El-Salam Canal water with brackish water. The results indicated that the application of FO/ RO hybrid system for desalination is a promising system in the case of high TDS draw solution (such as seawater) but it is not beneficial in the case of low TDS draw solutions (such as brackish water).
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