When it comes to the water-energy nexus, harnessing blue energy is vital with today’s energy-demanding processes and technologies. In this context, the reverse electrodialysis (RED) process is a thriving process that is serving as a potentially viable external energy source for many energy intensive processes such as membrane distillation (MD), electrodialysis (ED), capacitive deionization (CDI), etc. RED utilizes the Gibbs free energy of mixing two solutions of different salinities - salinity gradient energy (SGD) - and converts it into usable electrical energy. Hence, it is crucial to develop RED systems with an appropriate low concentration (LC) and high concentration (HC) solution pairs to maximize the extractable power density and at the same time make use of various disposable industrial effluent streams. Herein, this work explores using a compact RED system that converts the chemical potential energy of mixing ammonia-based industrial wastewater stream (LC) with a high effluent salinity brine stream (HC) into viable electrical energy. Simultaneously, the resultant brackish water level stream of this mixing process is properly diluted and used for fertigation to increase the sustainability of the process. As such, mixing those wastewater streams will eliminate the unadvisable disposal of high salinity brine directly back into the sea. The wastage of ammonia-rich wastewater can enhance agricultural productivity. The influence of concentrate and dilute stream concentrations, compositions and flowrates on acquired power density and energy recovery were investigated and gave maximum power density of 1.3 Wm<sup>-2</sup> in the tested RED cell, which is comparable with power densities achieved with conventional NaCl based solutions in the same system (2.0 Wm<sup>-2</sup>). Additionally, the impact of changing the number of ion exchange membrane pairs, amount of external load added, and recyclability of wastewater streams was studied and optimized to amplify the osmotically generated power and subsequently obtain the maximum power density from it, and also to increase the extent of wastewater dilution to reach brackish water levels suitable for irrigation.

Reverse electrodialysis (RED) enabling sustainable wastewater management for harvesting blue energy and fertigation

ACS Spring Meeting 2021

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