In regular RO, long membrane trains (6-8 elements long) are required to reach high recoveries (>80%). This keeps the flux and concentration polarization (CP) factor in the lead element reasonable to avoid excess fouling risk.
In batch RO, we can achieve 90% recovery with just a single element because permeate is recovered over multiple passes as feed recirculates during permeate production.
With batch RO, high-performance desalination is available to the smallest plants.
In regular RO, there is a major flux imbalance. A majority of freshwater is produced from the first several elements and the remainder is squeezed out of the last few elements. The average system flux (15 LMH) is substantially lower than the flux in the lead element.
Membrane manufacturers specify maximum element fluxes to avoid fouling.
In batch RO, the flux is balanced across the membrane train becuse the per-pass recovery is less than the overall recovery. This means less fouling potential and more freshwater production from the back end of the train.
We can boost batch RO design fluxes to 22 LMH and beyond without exceeding maximum element fluxes and with just a bit more energy:
Reduced fouling potential
Boosted production capacity
Shorter membrane trains