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UBC Theses and Dissertations

Ammonia gas recovery from waste streams using bipolar membrane electrodialysis : performance limiting study and system optimization Senanayake, Senanayake Mudiyanselage Aroshi Erandika


Ammonia is a versatile compound for fertilizer, refrigerant, and chemical production, as well as a potential hydrogen carrier for fuel cell vehicles. Wastewater is a sustainable ammonia source which can largely substitute the conventional ammonia production via the Haber-Bosch process. Bipolar membrane electrodialysis (BMED), combined with a membrane contactor, holds promise for electrified, chemical-free ammonia recovery from wastewater. However, ammonia leakage through the ion exchange membranes (IEMs) and limited recovery rates remain among the major challenges in implementing this new approach. Our study focuses on understanding these limitations and optimizing the BMED configuration. We first examine the mode of ammonia leakage through IEMs and find that its transfer across the membranes occurs as a gas phase. Subsequently, we investigate the relation between the cross-stack electric potential, as driving force for ammonia gas production, to the extent of ammonia leakage and its recovery efficiency. We find that a lower cross-stack potential slows down the ammonia leakage at the cost of reduced ammonia recovery due to the insufficient rate of water splitting inside the bipolar membranes. Then, the impact of mass transfer resistance across IEMs on the ammonia leakage and recovery is investigated by introducing multiple layers of IEMs. We find that there is an optimal number of IEMs layers that allows for minimizing ammonia leakage as low as 2% and achieving high ammonia recovery as high as 63%, along with an energy consumption comparable to industrial Haber Bosch process (0.6 MJ/mol-N). Finally, a new BMED configuration with an additional compartment of saline solution is examined as an alternative to prevent ammonia leakage. This configuration achieves an 86% recovery rate and virtually zero ammonia leakage but requires external chemical input. Our study highlights the potential of highly efficient ammonia recovery from wastewater using BMED through optimizing BMED operating parameters and configurations.

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