Pressure exchanger batch reverse osmosis with zero downtime operation

Batch reverse osmosis is a transient, pressure-driven desalination process that concentrates a given volume of feed over time by continuously recirculating the brine through the membrane module. Since it can closely follow the osmotic pressure of the brine, batch reverse osmosis consumes much less energy than conventional reverse osmosis. However, one of the key challenges with batch and semi-batch reverse osmosis has been to reduce the downtime required for recharging membrane module, pipes and batch tanks with fresh feed at the end of a batch. In this article, we describe a pressure exchanger batch reverse osmosis process that uses a set of two atmospheric pressure tanks which switch at the end of a cycle. Permeation through the membranes is held constant throughout the process, even during flushing, to effectively have zero downtime. The proposed system uses off -the-shelf components, can handle variable recovery, and is easy to scale-up and maintain. We study the system using a reduced order model that can capture external concentration polarization, non-ideal salt rejection, and osmotic backwash. The design is extended to a 100,000 gal per day capacity plant that demonstrates the scal-ability of the process while operating with a 2nd law efficiency of 48.2 %.