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Recycling nutrients (nitrogen, phosphorus, and potassium) from human urine can potentially offset more than 13% of global agricultural fertilizer demand. Biological nitrification is a promising method for converting volatile ammonia in high-strength human urine into stable ammonium nitrate (a typical fertilizer), but it is usually terminated in the intermediate production of nitrite due to the inhibition of nitrite-oxidizing bacteria by free nitrous acid (FNA). This study aimed to develop a stable nitrification process in a unique two-stage bioreactor by removing critical barriers associated with FNA inhibition. Experimental results show that half of the ammonium in high-strength urine was successfully converted into nitrate, forming valuable ammonium nitrate (with a nitrogen concentration greater than 1500 mg N/L). The ammonium nitrate solution could retain most phosphorus (75% ± 3%) and potassium (96% ± 1%) in human urine, resulting in nearly full nutrient recovery. Once concentrat