Recovery rate in desalination is the ratio of product water (permeate) flow to feed flow. In SWRO, the “optimal” recovery is the one that minimizes total water cost for a given project: pushing recovery higher can reduce capital needs, but raises operating cost because energy use increases as reject salinity rises; lowering recovery does the opposite, cutting energy use but requiring larger, more expensive equipment to produce the same permeate.
Most SWRO plants minimize total cost around 40–45% recovery, but higher recovery becomes attractive when intakes/outfalls, pretreatment, or capital are constrained or expensive. High recovery seawater desalination is now technically feasible through approaches such as ultra-high-pressure RO, multistage SWRO with different ERD configurations, and osmotically assisted RO, reaching >70% SWRO recovery or >45% brine recovery (brines >120 g/L TDS).
This paper assesses alternative process designs for achieving high recovery SWRO desalination. The economics for implementing these approaches are compared with each other and with those of conventional SWRO conducted at a more traditional 45% recovery rate.
