Hybrid Donnan dialysis–electrodialysis for efficient ammonia recovery from anaerobic digester effluent

Ammonia recovery from wastewater is crucial, yet technology of low carbon emission and high ammonia perm-selectivity against complex stream compositions is urgently needed. Herein, a membrane-based hybrid process of the Donnan dialysis-electrodialysis process (DD-ED) was proposed for sustainable and efficient ammonia recovery. In principle, DD removes the majority of ammonia in wastewater by exploring the concentration gradient of NH4+ and driven cation (Na+) across the cation exchange membrane, given industrial sodium salt as a driving chemical. An additional ED stage driven by solar energy realizes a further removal of ammonia, recovery of driven cation, and replenishment of OH- toward ammonia stripping. Our results demonstrated that the hybrid DD-ED process achieved ammonia removal efficiency >95%, driving cation (Na+) recovery efficiency >87.1% for synthetic streams, and reduced the OH- loss by up to 78% compared to a standalone DD case. Ammonia fluxes of 98.2 gN m-2 d-1 with the real anaerobic digestion effluent were observed using only solar energy input at 3.8 kWh kgN-1. With verified mass transfer modeling, reasonably controlled operation, and beneficial recovery performance, the hybrid process can be a promising candidate for future nutrient recovery from wastewater in a rural, remote area.