Encapsulation of waste incineration bottom ash by calcium alginate for enhanced phosphate removal from aqueous media

In this work, we use bottom ash (BA) encapsulated to millimetric-sized calcium alginate beads as a promising adsorbent material for potassium monophosphate removal from polluted water. The beads were prepared by millifluidic technique and used in either swollen or dried forms. The maximal adsorption capacity of the swollen and dried beads achieves 33.1±0.5 mg/g and 28.0±1.2 mg/g, respectively, and is rather insensitive to pH variation within the range 2<pH<11. The increased specific area and significant variation of the pore size distribution after phosphate adsorption suggest phosphate precipitation by calcium with possible formation of flake-like nanostructures as the main adsorption mechanism. Filtration though a compact bed of swollen BA containing beads allows for phosphate removal from initial concentration of 2 mg/L below the acceptable limit of 0.2 mg/L using only two cycles of a duration of 2h under gravity driven flow. From application perspective, this hybrid adsorbent combines several advantages such as: (a) possibility of waste (BA) valorisation; (b) environmentally friendly nature, low cost and biodegradability of alginate; (c) rather similar adsorption capacity in the broad pH range; (d) mechanical strength convenient for direct use in the filter bed; (e) prevention of heavy metal leaching from swollen beads during phosphate adsorption.