Abstract
A fertilizer drawn forward osmosis (FDFO) process was tested for the concentration of synthetic brine using an industrial-grade fertilizer ammonium sulfate (NH4)2SO4 as the draw solution (DS), NaCl-based synthetic brine as the feed solution (FS), and a commercial forward osmosis (FO) membrane. A bench-scale investigation and a pilot-scale investigation were carried out. By using the highest possible concentration of the DS with a fixed concentration of the FS, the brine generated by reverse osmosis (RO) desalination plants was simulated. The aim of this investigation, performed in batch mode, was to assess the feasibility of using the FDFO process with the tested DS to concentrate the brine by extracting water to dilute the DS. While the main aim of the investigated process was achieving the maximum possible volume reduction of the brine, the resulting DS was further diluted to reduce the nutrients’ concentration in the diluted DS to the acceptable levels producing fertilized water that can be used for fertigation. The investigation showed that the proposed process using the tested fertilizer resulted in an average water flux of 8.01 l/h/m2, and a volume reduction of the brine of around 12%.
Highlights
The production of potable water from both brackish and seawater using membrane desalination technologies, such as reverse osmosis (RO) and nanofiltration (NF), is becoming more common. Nayar et al (2019) reported that most of the seawater RO plants worldwide operate at an averageResponsible Editor: Angeles BlancoThe cost of disposal of seawater desalination brine into the sea is influenced by several factors such as the characteristics and volume of the brine, and the processes of pretreatment and disposal
A recent study showed that further extraction of water from desalination brine would result in significant reductions in disposal cost elements such as pipeline length and materials, as well as reductions in pumping energy and jet distance which would allow for the disposal in relatively shallow water bodies (Pistocchi et al 2020)
The bench-scale investigation was successful in identifying the maximum possible concentration of the tested industrialgrade (NH4)2SO4 in water, without the introduction of any external heating, which was found to be 740 g/l
Summary
The cost of disposal of seawater desalination brine into the sea is influenced by several factors such as the characteristics and volume of the brine, and the processes of pretreatment and disposal. The disposal of brine into the sea is estimated to be between 5 and 33% of the total cost of the desalination process, and increases in the case of inland desalination plants (Morillo et al 2014). In a desalination plant in Ras Shokeir, on the coast of the Red Sea in Egypt, 50,000 m3/day, EGP22 million (USD1.4 million), the cost of brine outfall was EGP1.6 million (USD102 thousands), amounting to 7.3% of the total CAPEX of the plant (El-Maraghy 2018). A recent study showed that further extraction of water from desalination brine would result in significant reductions in disposal cost elements such as pipeline length and materials, as well as reductions in pumping energy and jet distance which would allow for the disposal in relatively shallow water bodies (Pistocchi et al 2020).
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