Chitosan-Montmorillonite-Fe Nanocomposite Hydrogel for Phosphate Recovery and Reuse

Phosphorous (P) recovery from wastewater is a promising solution to the depleting nonrenewable phosphate rocks as the raw material for fertilizer production and to the eutrophication caused by excessive nutrient contamination in surface waters. This work explored the potential of an electrolyte biohydrogel based on chitosan as a phosphate sorbent and controlled releaser to recover the nutrient from wastewater and then release it as a fertilizer to food plants. Sorption kinetics and isotherm were quantified in batch experiments. The hydrogel reached saturation within 2 h, and the projected maximum phosphate sorption capacity was above 86.7 mg center dot g-1. Mathematic models and characterizations suggested that the sorption involved two main mechanisms: (i) electrosorption with cationic amine groups and (ii) ferric oxide hydrate ligand exchange. Versatile sorption pathways enabled stable capacity across a range of pH. In successive desorption experiments, 72.4% of the loaded P was continuously released over 16 days, a high content of which was bioavailable as indicated by the Mehlich 2 extraction test. With the additional water retaining capability, the P laden hydrogels have the potential to be reused in soil amendment as a controlled-release P fertilizer.