Treatment And Recovery of RO Brine for Higher Recovery in NEWater Factories

In the current NEWater production, brine generated from the reverse osmosis (RO) process is blended with secondary effluent and discharged to the sea. The RO brine therefore presents an additional source of water that is untapped, as it contains moderate to high concentration of ions and organics, which prevents its reuse.

The objective of the project is to develop a treatment process that is not constrained by water chemistry, and capable of recovering water from the currently untapped source of RO brine from the NEWater factories. Our aim is to increase water recovery of the NEWater factories to more than 95% at the required water quality with the treatment and recovery of RO brine. Correspondingly, the volume of brine discharged will be reduced to less than 5%, and thereby achieving waste minimisation.

The project’s approach uses the Capacitive Deionization (CDI) technology (Figure 1) as the core of the brine treatment process. The CDI targets at the removal of ions including divalent and trivalent ions in the RO brine that cause scaling at RO. The removal of these inorganic compounds is critical, in order to recycle the treated brine as feed water to the RO and thereby increase water recovery. The brine treatment process will also integrate a pretreatment to remove organics and other compounds that would otherwise foul the CDI.

Laboratory-scale results so far have met expectation. The CDI was able to recover 90% of the RO brine at the required water quality. Correspondingly, this implies that NEWater factory could potentially achieve more than 95% total water recovery. Currently, the project is moving on to pilot testing with a CDI unit of 5 m3/d capacity.

If successful, the positive implication derived from this project is the multiplying effect of water reuse, whereby we can increase our water resources by increasing recovery from the water reclamation loop. Concomitantly, for inland water reclamation facilities where disposal of untreated RO brine has potentially adverse impacts on the environment, this project could also provide a cost-effective alternative technology to water utilities for the management of their RO brine streams.

This project is a joint collaboration between PUB and NUS, and has been accepted and included as part of the European Union (EU) RECLAIM Water project under the EU's sixth Framework Programme for Research and Technological Development.