Evidence of solution-diffusion-with-defects in an engineering-scale pressure retarded osmosis system

• Published in: Journal of membrane science 2021-05, Vol.625, p.119135, Article 119135
• Main Authors: Binger, Zachary M., O'Toole, Galen, Achilli, Andrea
• Format: Article
• Language: English
• Subjects: Engineering-scale RO-PRO; Experimental PRO; Membrane defects; Pressure retarded osmosis; Seawater desalination; Solution-diffusion-with-defects model
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2021.119135

An engineering-scale seawater reverse osmosis-pressure retarded osmosis (SWRO-PRO) system was designed and deployed to evaluate the energy recovery during seawater desalination through salinity gradient energy. Experimental data on energy recovery and consumption were collected from a PRO system composed of up to five 4040 spiral-wound membrane elements, utilizing freshwater and RO concentrate to drive permeation. During experimental testing, specific energy recoveries as high as 0.14 kW h/m3 were achieved; however, energy consumption due to pressure losses in the system reduced the net specific energy recovery to a maximum of −0.07 kW h/m3. A 100% increase in energy recovery or 50% decrease in energy consumption would be necessary to yield a positive net energy recovery. Also, a combined approach of simultaneously increasing energy recovery and decreasing energy consumption would be a more desirable path for SWRO-PRO to become an energy positive technology. Experimental data were then paired with modeling software utilizing a solution-diffusion-with-defects model to demonstrate the presence and extent of defects in the membrane structure that allow for pressure-driven pore flow. The solution-diffusion-with-defect model explains the lower than expected water permeability and salt rejection often seen in experimental PRO results. Integrating this model into future software will allow for more accurate simulation of larger systems and aid in investigations of PRO scale-up. [Display omitted] •Multiple 4040 spiral-wound membrane elements were experimentally tested in a SWRO-PRO system.•Maximum specific energy recovery by the PRO system was 0.14 kW h/m3.•Energy consumption due to pressure losses exceeded energy recovery of PRO by approximately 100%.•A solution-diffusion-with-defects model best predicts water flux and salt rejection in PRO.•Defects on the membrane surface reduced power and energy recovery of PRO by approximately 30%.