Salinity gradient energy generation by pressure retarded osmosis: A review

Pressure retarded osmosis (PRO) has gained attention due to its use as a salinity gradient energy-generating membrane process. This process can convert difference in salinity between two streams into energy as it allows water transport through a semi-permeable membrane against the application of hydraulic pressure. This review provides a comprehensive look at the history and latest developments in preparation of membranes and modules for the PRO process, as well as the various applications of PRO. This review also explored the influence of feed characteristics and pretreatment strategies on water permeation and power generation during PRO operation. The current status and technological advancements of PRO as a process were reviewed, revealing how PRO can be operated as a stand-alone process or in integration with other hybrid processes. Despite the recent advancements in material and process development for PRO, membrane performance, wide-scale implementation, and commercialization efforts still leave much to be desired. Recognizing the current challenges facing the PRO technology, the advancements in PRO membrane and module development, and the various applications of the process, this review also draws out the future direction of PRO research and generation of osmotic salinity gradient energy as a viable energy source.