Forward osmosis technology: a combined exergy and exergoeconomic perpestive on system efficiency

Abstract

Water desalination has positioned itself as an essential alternative source of freshwater that allows to reduce the gap between the availability of freshwater and its continuously rising demand. Reverse Osmosis (RO), Multi-Effect Distillation (MED) and Multi-Stage Flash Distillation (MSF) are currently dominating the production of desalinated water with 94% of the global total. Emerging desalination technologies have appeared over the past decades, as a result of efforts to improve conventional desalination techniques, being Forward Osmosis (FO) one of the most promising due to its potential lower energy requirements, higher fouling resistance, and potential for Zero Liquid Discharge (ZLD). This study presents an exergy and exergoeconomic analyses of a Forward Osmosis pilot plant designed for wastewater treatment, in order to evaluate system efficiency and identify opportunities for optimization. Results indicate that the FO membrane module achieved an exergy efficiency of 45.6%, being in line with typical values obtained in membrane-based technologies. The feed and draw pumps presented 0.45% and 0.60% of exergy efficiency respectively, mainly attributed to its oversized disign. Exergoeconomic analysis further confirmed the membrane module as the most cost-effective component, highlighting the feed and draw pumps as key targets for performance and cost improvement.