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

Abstract

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.