Indirect desalination of Red Sea water with forward osmosis and low pressure reverse osmosis for water reuse Original Research Article

The use of energy still remains the main component of the costs of desalting water. Forward osmosis (FO) can help to reduce the costs of desalination, and extracting water from impaired sources can be beneficial in this regard. Experiments with FO membranes using a secondary wastewater effluent as a feed water and Red Sea water as a draw solution demonstrated that the technology is promising. FO coupled with low pressure reverse osmosis (LPRO) was implemented for indirect desalination. The system consumes only 50% (~ 1.5 kWh/m³) of the energy used for high pressure seawater RO (SWRO) desalination (2.5–4 kWh/m³), and produces a good quality water extracted from the impaired feed water. Fouling of the FO membranes was not a major issue during long-term experiments over 14 days. After 10 days of continuous FO operation, the initial flux declined by 28%. Cleaning the FO membranes with air scouring and clean water recovered the initial flux by 98.8%. A cost analysis revealed FO per se as viable technology. However, a minimum average FO flux of 10.5 L/m²-h is needed to compete with water reuse using UF–LPRO, and 5.5 L/m²-h is needed to recover and desalinate water at less cost than SWRO.