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13The removal of nutrients (nitrogen (N), phosphorous (P)) from waste water has become a resource 14 recovery option in recent regulations worldwide, as observed in the European Union. Although both 15 of these nutrients could be recovered from the sludge line, more than 70-75% of the N and P is 16 discharged into the water line. Efforts to improve the nutrient recovery ratios have focused on 17 developing low-cost technologies that use sorption processes. In this study, a natural zeolite 18 (clinoptilolite type) in its potassium (K) form was impregnated with hydrated metal oxides and used to 19 prepare natural hybrid reactive sorbents (HRS) for the simultaneous recovery of ammonium (NH4 + ) 20 and phosphate (PO4 3-) from treated urban waste water. Three unfertile soils (e.g., one acidic and two 21 basic) amended with N-P-K charged HRS were leached with deionized water (e.g. to simulate 22 infiltration in the field) at two-and three-day time intervals over 15 different leaching cycles 23 (equivalent to 15 bed volumes). The N-P-K leaching profiles for the three charged hybrid sorbents 24 exhibited continuous nutrient release, with their values dependent on the composition of minerals in 25 the soils. In the basic soil that is rich in illite and calcite, the release of potassium (K + ) and ammonium 26 (NH4 + ) is favoured by-ion exchange with calcium (Ca 2+ ) and accordingly diminishes the release of 27 phosphate (PO4 3-) due to its limited solubility in saturated calcite solutions (pH 8 to 9). The opposite is 28 true for sandy soils that are rich in albite (both acidic and basic), whereas the release of NH4 + and K + 29 was limited and the values of both ions measured in the leaching solutions were below 1 mg/L. Their 30 leaching solutions were poor in Ca 2+ , and the release of PO4 3-was higher (up to 12 mg P-PO4 3-/L). 31 *Revised manuscript with no changes marked Click here to view linked References 2The nutrient releases necessary for plant growth were provided continuously and were controlled 1 primarily by the soil mineral dissolution rates fixing the soil aqueous solution composition (e.g. pH 2 and ionic composition; in particular, the presence of calcite is a determinant for nutrient release, 3 especially in alkaline soils). The N-P-K charged HRS sorbents that were used for soil amendment 4 may be an alternative for avoiding nutrient leaching and reaching the goals of soil sustainability in 5 agriculture and reducing the nutrient overloading of surface waters. 6

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