Pilot plant investigation of a spiral wound membrane module performance for Osmotically Assisted Reverse Osmosis (OARO) process: analysis and simulation of an industrially-relevant case study

Osmotically assisted reverse osmosis (OARO) is a novel membrane-based process which can be implemented as a Zero Liquid Discharge (ZLD) technology for wastewater treatment. This study analyzes OARO process and evaluates its effectiveness for treating highly concentrated solutions. Pilot-scale tests were conducted on a prototype membrane in different ranges of feed and sweep concentrations of NaCl. Positive water fluxes were achieved, even for highly concentrated feed solutions, ranging from 1.00-4.60 LMH at feed pressures from 20 to 28 bar for feed concentrations from 1 M to 4 M of NaCl. Results revealed challenges such as concentration polarization, membrane telescoping under high pressures and dilution of the sweep solution, all of which impact water flux and process efficiency. Then, OARO simulation using experimental data was conducted to explore the process performance in a textile sector application, highlighting energy efficiency advantages of hybrid membrane-assisted ZLD systems over traditional thermal treatment. Three treatment configurations were analyzed: (1) system based on multi-effect evaporation, (2) hybrid system integrating OARO before multi-effect evaporation, (3) hybrid system integrating Ultra-high Pressure Reverse Osmosis (UHPRO) before multi- effect evaporation. Results indicated that the configuration using only thermal treatment presented the highest specific energy consumption (SEC). Both membrane-based processes allowed a significant reduction of energy duties. UHPRO-based configuration demonstrated slightly lower SEC compared to OARO in a base-case scenario. However, opportunities for OARO optimization were identified, which could significantly improve the energetic performance by integrating pressure recovery devices. Moreover, OARO operation at lower pressures offers economic benefits through the use of cost-effective standard components, reducing associated costs. These advantages highlight OARO potential as an energy-efficient and cost-effective solution for industrial wastewater treatment.