Improving Desalination Recovery Using Zero Discharge Desalination (ZDD): A Process Model for Evaluating Technical Feasibility

Zero Discharge Desalination (ZDD) is a very high-recovery hybrid desalination system, typically comprised of a primary desalter (such as reverse osmosis (RO) or nanofiltration (NF)) and electrodialysis metathesis (EDM). The EDM acts as a "kidney" by removing troublesome salts from the concentrate of the primary desalter, which allows for additional recovery of potable water. A mathematical model was developed to simulate ZDD system performance using mass balance, desalination design equations, and experimental data. Model results confirm that ZDD can achieve >97% system recovery for brackish water with (a) a feed total dissolved solids (TDS) concentration of <3 g/L; (b) relatively high fractions of multivalent ions (e.g., calcium and sulfate mass concentrations of >60% of the TDS); and (c) a silica content of <40 mg/L. Furthermore, model results indicate that 0.77 kWh per 1 g/L of feed TDS; (b) increases with lower decreases with higher recovery on the primary desalter (e.g., RO g/L of feed TDS. Higher TDS feedwater (e.g., 3.5 to 5 g/L) 1 the required ZDD specific energy consumption (a) increases by permeate TDS, especially below 500 mg/L; and (c) generally or NF). ZDD system recovery generally decreases by 1% per 1 imits ZDD system recoveries to 94% to 90%, respectively.