Stabilization and concentration of nitrogen in synthetic urine with peracetic acid and progressive freeze concentration

Peracetic acid (PAA) was used as an inhibitor to prevent urea hydrolysis in the recovery and concentration of nitrogen in a synthetic urine. Twenty mg/L of PAA was found to be effective in inhibiting urea hydrolysis for seven days before it was concentrated by the progressive freeze concentration (PFC) process. Ammonia concentration, total nitrogen (TN), pH, and electrical conductivity (EC) were monitored. The PFC process, operating with a coolant temperature of − 12 °C and a stabilized synthetic urine temperature of 23 °C, reduced the volume of the stabilized synthetic urine by approximately 80% (concentration factor of 5.1) and concentrated the TN approximately 21,000 mg/L with ammonia concentration of approximately 50 mg/L-N. Seven days after the PFC treatment, the urea in the concentrated synthetic urine continued to be fairly stable although addition of PAA may be needed to stabilize the concentrated solution further. The experimental results showed that a combination of using PAA as an oxidizing agent and the PFC process can be an effective and suitable process for source separation systems to concentrate urine to recover nitrogen and produce liquid fertilizer.