ZLD Without Evaporation: Saltworks Achieves First ZLD With a Membrane Crystallizer

How did we do it?

Our engineers hybridized UHP-RO with a chilled crystallizer system, in a semi-closed loop that concentrates water, extracts solid salt, and repeats the cycle. The UHP-RO system can concentrate certain salts (e.g. sodium sulfate) to over 20% by mass. Examples of suitable ions include: Na⁺, K⁺, NH₄⁺, CO₃^2-, and SO₄^2-. The concentrated brine solution then enters our chilled crystallizer, which takes advantage of steep solubility changes with temperature. There, the solution cools, resulting in the formation of salt crystals, which can be separated and removed.

After cooling and salt extraction, the residual brine liquor has a lower dissolved salt content (~10%) and can be warmed up and recycled once again through the UHP-RO system. A heat pump is used to simultaneously cool one part of the circuit while heating the other — presenting considerable energy efficiency savings. As the loop operates, it continuously produces reverse osmosis quality permeate and solid salt crystals, while being replenished with make-up wastewater. No boiling means less energy consumed and lower costs.