Techno-economic evaluation of maximizing minimum liquid discharge from seawater desalination for the fertilizer industry

The Middle East and North Africa region faces critical water scarcity and food security challenges that threaten economic development. Fertilizer use supports food self-sufficiency, but its production is highly water intensive. Supplying desalinated water to a decarbonized fertilizer plant offers an environmentally sustainable pathway.<br/><br/>This study investigates co-locating a decarbonized fertilizer plant with a seawater desalination facility, optionally implementing minimum liquid discharge (MLD) to generate additional revenue through recovery of magnesium hydroxide and sodium chloride (NaCl). Three configurations were modeled: a conventional seawater reverse osmosis (SWRO)-based plant; and two MLD configurations using high-pressure RO (HPRO), osmotically-assisted RO (OARO), and crystallizers. Financial performance was assessed using a novel discounted and allocated levelized cost (DALC) method, internal rate of return (IRR), and net present value (NPV).<br/><br/>In a Moroccan case study, the conventional configuration achieved the lowest DALC and energy consumption (0.70 USD/m3water and 3.8 KWhel/m3), with an IRR of 23.9 %. The first MLD configuration had higher costs (0.94 USD/m3water, 12.0 KWhel/m3) and a lower IRR (14.5 %), with water recovery limited to 71.4 % due to nonuse of magnesium crystallizer effluent (60.4 % in the conventional setup). Reusing this effluent in the second MLD configuration increased water recovery to 96.7 %, yet higher impurities at the NaCl crystallizer feed reduced the IRR to 9.7 %, which could be improved through financing strategies such as lowering capital costs to endorse the MLD-maximizing option.<br/><br/>The findings emphasize advancing impurity removal methods and exploring innovative project financing strategies to enable financially and environmentally sustainable seawater desalination for decarbonized fertilizer production.