Performance of a SWRO membrane under variable flow conditions arising from wave powered desalination

A wave-powered desalination unit couples a wave energy converter and reverse osmosis (RO) membrane to produce fresh water from pressurized seawater. Although renewable energy technologies have been increasingly used for desalination, the concept of direct wave-powered desalination system is still at an early stage of development. One of the challenges with direct wave-powered desalination is that while reverse osmosis (RO) membranes are typically designed to operate at a constant feed flow and pressure, wave energy converter outputs in the form of hydraulic pressures and flows are typically highly variable. In this work, a RO membrane is investigated under variable feed flow conditions to determine the potential impact of such operation on membrane performance. The feed flow and pressure are varied using both a traditional sinusoidal profile and a rectified sinusoidal profile - a case more representative for wave-powered desalination. The permeate recovery and permeate salinity for both cases are compared with the equivalent time-averaged steady-state conditions. For purely sinusoidal flow, the performance of the RO membrane was similar to the equivalent steady-state flow conditions. For rectified sinusoidal flow, there is a marginal increase in permeate recovery, while a significant increase in permeate salinity is observed. In addition, a membrane integrity test was carried out after both sets of varying flow conditions. A significant change in membrane performance was detected after the test with the rectified sinusoidal flow.