| Summary: | In this study, we tested a bench-scale prototype of a true batch reverse osmosis (RO) system using a
flexible bladder and a 2.5 in. (6.4cm) spiral wound membrane element. In theory, batch RO systems can
achieve the lowest practical energy consumption by varying feed pressure over time. However, this is
the first study to validate batch models by measuring the hydraulic work of both the high pressure pump
and the circulation pump. The experimental measurements agree well with the model (error < 3%) after
accounting for concentration polarization.
We used the validated model to calculate the energy savings of true batch systems at higher salinities
and recovery ratios. Previous studies assumed that a batch RO plant would operate at the same flux and
steady-state feed salinity as a comparable continuous RO plant. In order to match the permeate
production of a continuous RO plant, a batch RO plant must operate at an elevated flux to offset its
intermittent permeate production. A batch RO plant will operate at a steady-state feed salinity higher
than the plant’s intake feed salinity due to salt retention between batch cycles. As a result of these
practical inefficiencies, the energy savings achievable by true batch systems are less than previously
thought, but still significant at relatively high recoveries. At 50% recovery of seawater feed, a batch
system could save 11% of the energy consumed by a continuous RO system while still maintaining the
same level of permeate production. We have demonstrated the successful operation of a true batch
system and shown that it can indeed reduce energy consumption.
Keywords: batch reserve osmosis; true batch; energy efficiency; energy savings; system design
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