Wastewater with high-concentration urea can be treated by freeze concentration effectively.The determination of freeze concentration limitation is necessary for forecasting and evaluating the efficiency and maximal water recovery rate of freeze concentration.The phase change of urea solution during the freezing process was analyzed with differential scanning calorimetry (DSC).The solution concentration at the eutectic point of urea was determined by freezing experiment.Urine was adopted as the sample to study the method for determining the freeze concentration limitation of wastewater containing high-concentration urea.It was found that when the urea concentration of wastewater was higher than 26.3%

urea would crystallize with ice before the freeze concentration limitation.The wastewater became glass state at the end point of freeze concentration.The maximal water recovery rate of the freeze concentrate technology and the glass transformation temperature of solution can be determined by DSC. DSC analysis showed that the glass transformation temperature of urine was -108.33℃

the corresponding solution concentration of maximal freeze concentration was 57.92%

and the maximal water recovery rate was 97.75%.