Urine drying with ash and lime at temperatures 20-60°C : nutrient recovery from source separated urine

Abstract: Utilization of source-separated urine in agricultural production has been practiced and different treatment options have been developed in last two decades. The purpose of this study was to develop a drying technique for untreated human urine added to ash and lime as drying agent at temperature 20-60°C. A solid urine fertilizer was expected as final product that will be easy to transport and apply on agricultural field. In this study, a mixture of ash and lime (1:1 by weight) was used as drying agent and human urine was applied as undiluted and fresh. The reason behind using ash and lime was to maintain a pH>10 during drying process, which should inhibit urea hydrolysis in urine, and thereby urea should be retained in drying agent. The drying technique was developed and drying capacity was quantified. Concentration of ammonia nitrogen was measured photometrically. A mass balance for nitrogen was obtained. It was evident from the experiment that urea can be retained by maintaining a high pH (>10). Bad drying condition due to reduced evaporation rate, flooding of urine over drying agent, blockage in airflow have been identified as factors regulating nitrogen loss and the concentration of nitrogen in the final product. According to the experiment, urine drying at 20°C is not a feasible option, since rate of evaporation is very low. The highest retention of nitrogen (in the form of urea) at 35 and 60°C were 74% and 54% respectively.