Rapid and wide pH-independent ammonium-nitrogen removal using a composite hydrogel with three-dimensional networks

Chitosan grafted poly(acrylic acid)/unexpanded vermiculite (CTS-g-PAA/UVMT), a granular composite hydrogel with three-dimensional networks, was prepared via in situ graft polymerization and evaluated as the adsorbent to remove ammonium-nitrogen (NH4-N) from aqueous solution using batch adsorption experiments. The effects of various experimental parameters on NH4-N removal, such as vermiculite content, pH, contact time, NH4-N concentration and co-existing PO4-P ion were investigated. The adsorption capacities in different water bodies including distilled water, tap water, well water and lake water were compared to study further the influence of ion strength on NH4-N removal. The results indicate that the adsorption equilibrium can be achieved within a few minutes and the maximum, constant adsorption capacity can be observed in a wide pH range of 4.0–8.0. The adsorbent can exclusively adsorb NH4-N in the mixing solution containing NH4-N and PO4-P, suggesting that the electrostatic attraction dominates the whole adsorption process. Five consecutive adsorption–desorption studies show that the composite hydrogel has higher adsorption and desorption efficiencies, suggesting the potential of the as-prepared adsorbent for NH4-N removal.

► We develop a granular composite hydrogel with three-dimensional networks.
► The hydrogel shows fast adsorption rate and high adsorption capacity for NH4-N.
► The hydrogel has maximum and constant adsorption capacity in a wide pH range.
► The hydrogel can exclusively absorb NH4-N in the solution containing NH4-N and PO4-P.
► The hydrogel can be easily regenerated with no obvious loss in adsorption capacity.