Establishing the optimal condition for nutrient recovery from domestic wastewater using the freeze concentration method

The freezing concentration method is one of the potential techniques for recovering nutrients from wastewater. In this study, the method of freeze concentration was studied to establish its optimal conditions in recovering nitrate-nitrogen and phosphate nutrients from domestic wastewater. Water in the form of an ice crystal block is produced and leaves behind a solution with a higher concentration. The effects of coolant temperature from −10 to −80 °C, freezing time from 1 to 8 h, and energy consumption on nutrient recovery were investigated. The optimal conditions were found at a coolant temperature of −20 °C, freezing time of 7 h, and energy consumption of 0.197 kWh/L that resulted in the highest nitrate-nitrogen and phosphate nutrient recovery values of 1.114 and 4.667, respectively, at the inlet of anaerobic digester 1; 1.325 and 4.975, respectively, at the outlet of anaerobic digester 1; 1.099 and 4.859, respectively, at the inlet of anaerobic digester 2; 1.132 and 4.755, respectively, at the outlet of anaerobic digester 2; and for gravel filter at the outlet the values were 1.111 and 4.861, respectively. The recovered nutrients can be used as biofertilizers.