The implementation of the concept of sustainable and circular (bio)economy encourages the use of by-products from the food industry as valuable resources. This project investigates the potential application of brewer’s spent grain, buckwheat hulls, and waste fungal biomass as sustainable biosorbents for the removal of various water contaminants. The research includes physico-chemical and morphological characterization of the initial materials, as well as of the newly developed materials (biosorbents) obtained through different modification procedures of initial materials aimed at enhancing their biosorption properties. The efficiency of the newly developed biosorbents will be assessed through batch and continuous biosorption experiments, accompanied by analyses of their regeneration potential and the phytotoxicity of the treated water.