Ammonium removal and recovery from municipal wastewater by ion exchange using a metakaolin K-based geopolymer

•Ammonium recovery from real municipal wastewater in a continuous flow plant process.•Ammonium adsorption test on saline wastewater characterized by cations competition.Geopolymer granules showed high ammonium selectivity and adsorption capacity•Geopolymer granules did not deteriorate after adsorption/regeneration cycles.•Geopolymer allows to obtain a Na-free desorbed product potentially good as fertilizer.