Nutrient recovery from human urine is a promising pretreatment of domestic wastewater and provides a sustainable recyclability of N and P. In this study, batch experiments were conducted to identify the characteristics of natural loess (NL) for the adsorption and recovery of ammonium and phosphate from hydrolysis urine (HU). The adsorption mechanisms, the adsorption kinetics and isotherms, as well as the major influencing factors, such as pH and temperature, were investigated. Results revealed that adsorption of ammonium occurred by means of ion exchange and molecule adsorption with the ≡ Si-OH groups, while phosphate adsorption was based on the calcium phosphate precipitation reaction and formation of inner-sphere complexes with ≡ M-OH groups. The adsorption processes of ammonium and phosphate were well described by the pseudo-second-order kinetic model and the Freundlich isotherm model. Adsorption of phosphate was endothermic, while ammonium adsorption was exothermic. Furthermore, the maximum ammonium and phosphate adsorption capacities of NL was 23.24 mg N g(-1) and 4.01 mg P g(-1) at an initial pH of 9 and 10, respectively. Results demonstrated that nutrient-adsorbed NL used as compound fertilizer or conventional fertilizer superaddition was feasible for its high contents of N and P as well as its environmental friendliness.
Nutrient recovery from human urine is a promising pretreatment of domestic wastewater and provides a sustainable recyclability of nitrogen (N), phosphorus (P), and potassium (K). In this study, we present a method to recover all nutrients from hydrolysis urine (HU) in the form of solid products by combining acidification with evaporation-crystallization. The effect of initial pH (pH) on N retention was investigated, and the optimal pH was further determined by analysis of N retention efficiency. Additionally, crystallization process and product composition based on different pH-adjusted acids were also compared. The results revealed that pH of HU was the key factor for N retention, and the optimal pH was 4. In addition, compared with HCl and HSO, acidification by HPO could effectively reduce energy consumption and improve nutrient content in urine-derived solid products (UDSPs) but increase the acid consumption. The major compositions (mass percentage, %) in UDSPs-Cl, UDSPs-S, and UDSPs-P were salammoniac (80%), lecontite (41%) and ammonium nitrate sulfate (30%), and biphosphammite (84%), respectively. The results also demonstrated that the method of mixing of UDSPs-Cl/UDSPs-S and UDSPs-P and addition of fillers such as calcite, ground limestone, or ground dolomite into them is suitable for improving nutrient balance and fertilizer efficiency.
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