Co-immobilization of clinoptilolite and nanostructured hydrated ferric-zirconium binary oxide via polyvinyl alcohol-alginate covalent cross-linking for simultaneous deep removal of aqueous low-level nitrogen and phosphorus

A novel absorbent, PVA/SA-CFZ, was developed by jointly enveloping nanostructured hydrated ferric-zirconium binary oxide and clinoptilolite in the cross-linking of polyvinyl alcohol (PVA)/sodium alginate (SA). As a result, the cation exchange capacity of clinoptilolite and electrostatic attraction capacity of hydrated ferric-zirconium binary oxide can be integrated for the simultaneous removal of nitrogen and phosphorus from wastewater. The adsorption behavior of PVA/SA-CFZ for the co-existing ammonium and phosphate was primarily investigated by batch experiments. Over a wide pH range (4 ~ 11), PVA/SA-CFZ always showed the excellent adsorption performance both for the low-concentration ammonium (<5 mg/L) and phosphate (<0.5 mg/L), which reflected the well adaptability towards unfavorable environmental conditions. The kinetic analysis indicated that the pseudo-second-order kinetic model could quantitatively describe the adsorption process optimally. The mechanistic investigation revealed that ammonium was captured through the cation exchange reaction with clinoptilolite. The electrostatic attraction, inner sphere complexation with Fe/Zr-O-OH groups, and formation of phosphate precipitation jointly contributed to the fixation of phosphate by PVA/SA-CFZ. Generally, it is believed that PVA/SA-CFZ can serve as a promising composite absorbent for the simultaneous deep removal of nitrogen and phosphorus, and support for the advanced treatment of wastewater containing low-level nutrients.