Maximizing RO System Recovery: Real Time Scaling Ion Measurement and Selective Removal

Abstract:

Reverse osmosis (RO) is the dominant municipal and industrial desalination technology due to low costs and energy consumption. However, freshwater recovery of most RO systems is well below osmotic pressure limits because of scaling and fouling risk, or conservatism in design and operations on variable inlet water chemistry. With the advent of ultra high-pressure (UHP) RO, and focus on reducing energy consumed by thermal systems, maximizing RO recovery has become even more important. There are opportunities for impactful incremental innovation to maximize RO’s potential.

Saltworks has reviewed a sample set of forty USA-based industrial RO projects, finding that none were maximizing RO’s potential. Of these:

• 5% (3) were operating up to scaling saturation limits, and thus at maximum recovery without scaling ion removal
• 65% (26) were operating at 65-80% of the scaling saturation limit, revealing the potential for 20-35% additional recovery through operational and hydraulic improvements
• 5% (11) were well below the scaling saturation limit, revealing significant potential to boost recovery at low, incremental cost

All projects held potential to achieve additional recovery gains, however this necessitates investment, ranging from low to high. This work will review those options and provide designers with an understanding of the state-of-the-art of ‘bolt on’ RO recovery boosting technology, upon which future innovations may build. We focus on technologies that can be applied to any RO unit: conventional, semi-batch processes, counter flow, etc.

Lowest cost interventions include dynamically controlling RO recovery while protecting membrane health, based on real time, automated measurement of scaling ions. Moderate cost options include lowering scaling ion concentration through RO-friendly processes while adding membrane area, but not increasing the pressure rating of the RO unit under consideration. Higher cost options include combinations of the above alongside UHP RO, operating at 1,800 psi. Even highest cost options are typically more economic than evaporators, depending on scale. This work will summarize these emerging RO recovery boosting technologies, agnostic of the underlying RO configuration. The intent is to provide reviewers with state-of-art knowledge from which others can innovate.