Ammonium Removal and Recovery from Mainstream Anaerobic Effluent Using Hydrogel Packing Column

Considering the strict discharge limits and the circular economy policies, it is of specific interest to remove and, ideally, recover nutrients (NH4+-N in this study) from the effluent of anaerobic membrane bioreactors (AnMBRs) to expand their deployment in domestic wastewater (DWW) treatment. Herein, poly (acrylic acid) (PAA) hydrogel-based adsorption/desorption was for the first time proved to be a robust post-treatment strategy for AnMBRs treating DWW. Batch experimental results revealed that the adsorption of NH4+ ions by PAA hydrogels was a physical process involving electrostatic attraction and ion exchange, which favoured the fast uptake and facile elution. In our continuous column operation, we obtained up to 98.5% removal of NH4+-N from the AnMBR effluent, achieving a polished effluent with <1.5 mg NH4+-N/L. The hydrogel column showed nearly constant adsorption capacities over 10 rounds of regeneration, which warranted the economic feasibility in real practices. Crucially, an ammonium concentrate with a concentrating factor of ~10 was produced by reusing the eluent (1 M HCl) in the column for five times. This strategic eluent recirculation was for the first time proved to be an effective approach to concentrate NH4+-N from AnMBR effluent as a resource. In addition, the proposed process was estimated to be economically attractive according to our cost analysis, highlighting its promise as a cost-effective method for NH4+-N removal and recovery from AnMBR effluent