A Novel Renewable Energy Powered Zero Liquid Discharge Scheme For RO Desalination Applications

This work proposes a conceptual model for a Zero Liquid Discharge (ZLD) for Reverse Osmosis (RO) desalination. The model describes a Process Flow Diagram (PFD). The proposed process relies on an RO followed by electrolyser, solar evaporator and mixing tank. The water reject from the RO is split into three fractions, one to an electrolyser to produce H2, another to solar evaporator to produce fresh water, third is remixed with water from the evaporator to reduce the salinity of the RO feed. The hydrogen produced in the electrolyser is burned and its energy is stored using cement blocks. The evaporator is operated using solar energy during the sunny period of the day. Then, the energy stored in cement will replace the solar energy during the remaining hours of the day. The proposed model is based on mass and energy balances including the performance characteristics of individual equipment. A new parameter pZLD is defined as the ratio of the brine reject from the overall plant to the fresh brackish water drawn from the wells. The minimum value of pZLD is zero. The theoretical model is tested for desalination of brackish water with 8000 ppm Total Dissolved Solids (TDS). For a small capacity of 2,000 L/d of fresh water produced, the following results were reported for 400 ppm fresh water: water from well = 2,108 L; produced H2 = 7.40 kg/d; cement required = 2,160 kg for 14 h; solar energy = 5.04 kW for 10 h; pZLD = 5.8%. The cost of modifications to conventional desalination unit is 533,028 Egyptian Pound (EGP), (capital) and 323.49 EGP/h (operating)