Direct experimental comparison of batch reverse osmosis (RO) technologies

Batch RO technologies can help fulfil the growing need for high-recovery desalination. Several experimental studies have given results for batch and semi-batch RO processes individually, but under differing conditions. There is a lack of side-by-side comparisons. Here we report, for the first time, experiments with a high-pressure RO system that can be operated in batch, semi-batch, or hybrid semi-batch/batch mode. Using the same membrane and supply pump at pressures up to 110 bar, we compare performance against semi-batch mode which is used as the baseline throughout. With seawater feed, batch RO reduces electrical SEC by 10 % at recovery of 0.655. With brackish water feed, we use hybrid mode to avoid an excessively large work exchanger volume. Working at recovery of 0.94, a work exchanger volume of 20 L reduced SEC by 23 %. A work exchanger volume of 40 L reduced SEC further, resulting in SEC of 1.81, 1.89 and 2.02 kWh/m3 at recoveries of 0.9, 0.92 and 0.94 respectively, thus representing a 22–32 % reduction against the semi-batch baseline. The results also showed permeate conductivity reduced by up to 50 %. The study confirms the advantages of batch and hybrid RO over semi-batch RO, especially for brackish water desalination at high recovery.