Zeolites for the nutrient recovery from wastewater

To meet the growing food demand of the world population, excessive use of chemical fertilizers is occurring to improve soil fertility and crop production. The excessive use of chemical fertilizers is not economically and environmentally sustainable. Indeed, from one hand, due to the increasing demand of fertilizers is rising their costs whereas, on the other hand, the accumulation of fertilizers in wastewaters is altering the homeostasis of the ecosystems thus causing serious damages to human health [1,2]. The recovery of nutrients, such as nitrogen (N) and phosphorus (P), from wastewaters is a good option to counteract both economic and environmental issues raised by the excessive use of fertilizers [3]. Adsorption is among the most widely used methods for nutrient recovery from wastewaters due to its efficiency and simplicity. The choice of appropriate adsorbent materials is a key issue for ensuring high performance and low costs of the process [4]. Over the years, several materials have been studied to absorb nutrients from wastewaters. Zeolites, both natural and modified, have attracted great attention due to their relevant specific capacity, selectivity, safety, and stability [5]. However, considering that in municipal effluents the inorganic P exists as the anionic forms of dihydrogen or monohydrogen phosphates (H2PO4 − and HPO42−, respectively) and N in both cationic (ammonium, NH4+) and anionic (nitrate, NO3−) form [6], natural zeolites can be only used for the direct recovery of NH4+.