With phase I of the WaterFX demonstration plant with the Panoche Water and Drainage District complete, we are now moving into Phase II, which will prove that solar desalination can achieve zero discharge.
Zero discharge desalination (ZDD) using Aqua4™ overcomes two hurdles that have consistently plagued conventional seawater desalination: low water recovery and high brine disposal costs. Unlike conventional seawater desalination, the Aqua4™ process does not generate waste brine and instead utilizes ZDD to produce only freshwater and solid salt as co-products. Reverse osmosis (RO), the leading seawater desalination process, operates at only 50% recovery and requires the discharge of the remaining 50% brine back into the ocean, resulting in one of the primary hurdles to broad adoption of desalination. In contrast, ZDD operates at greater than 90% recovery and utilizes post processing to convert the remaining high concentration brine into salt crystals. High recovery desalination allows the brine to be sent to a salt crystallizer at concentrations of > 20% dissolved solids, making it economical to recover valuable compounds for resale. Once recovered and separated, these salt compounds are used for a variety of chemical and industrial applications, such as building products, fertilizers, health supplements and metals recovery. Eliminating the cost of brine disposal and capturing the value of recoverable compounds has a significant impact on the economics and potential for desalination to serve as a primary source of freshwater.
In the past, ZDD has been prohibitively expensive due to the low recovery of RO and the high cost of crystallization. However, by driving up the overall recovery using solar thermal desalination (multi-effect distillation) the volume of brine that needs to be processed is reduced to 7% of the overall process flow (Aqua4™ operates at 93% recovery) and brine concentrations exceed 210,000 ppm TDS; thus significantly reducing the size and cost of the crystallizer. Commercially available crystallization equipment can be utilized for this purpose and the overall ZDD process adds less than 5% to the total energy requirements of solar desalination. Further, when solar desalination is used to clean up a discharge stream rather than desalinate seawater, ZDD is critical for achieving full treatment.
If you have any questions about the Aqua4™ process, we encourage you to leave a comment or contact us. Our mission is to build a growing community that is working together to solve water scarcity.
Composition of solid salt samples produced at the WaterFX demonstration plant: Sodium Sulfate, Sodium Chloride, Calcium Sulfate, Calcium Chloride, Magnesium Sulfate, Sodium Carbonate, Calcium Carbonate, Sodium Nitrate, Magnesium Chloride, Calcium Borate, Silica, various trace minerals (< 0.005%)