Competitive fixed-bed biosorption of Ag(I) and Cu(II) ions on Sargassum filipendula seaweed waste

•Application of an abundant waste from alginate production in wastewater treatment.•Optimal inlet flow rate in dynamic biosorption of Cu2+/Ag+ is between 0.5-0.75 mL.min-1.•Investigation of the biosorption capacity, breakthrough and mass transfer zone regarding inlet composition.•Selective desorption of Cu2+ (99.8%) and Ag+ (90.7%) ions for further applications.•Highly concentrated copper samples from the desorption operation.