Recovery of Ammonia from Human Urine by Stripping and Absorption

Separately collected human urine contains valuable nutrients including nitrogen, phosphorus, and potassium. This study concerns the removal and recovery of ammonia from urine by stripping and absorption processes. Throughout the experiments, ammonia was stripped with air in a batch system and absorbed in sulphuric acid solution. Combined mass transfer coefficient (KL × a) for urine–air interaction, was calculated for different pH levels and air flow rates, by using a spherical stripping unit equipped with a ceramic fine-pore air stone (average pore size 40 microns). (KL × a) was observed to increase with increasing pH level and air flow rate. The highest value of combined mass transfer coefficient was 0.48 h−1 , obtained at a pH of 12 and an air flow rate of 0.27 m3/h. In the stripping process, a direct relationship was observed between air flow rate and mass transfer rate. At an air flow rate of 0.21 m3/h, and at pH 12, the highest mass transfer rate (0.085 g/h) was obtained. In the absorption unit, averagely 92% of ammonia was recovered as ammonium sulphate. In the predesign calculations stripping factor, desired removal rate and the volumetric flow rate of urine and sulphuric acid were estimated. According to estimated values, a stripping column having a 1 m diameter and 2.5 m packing height (packing: ceramic raschig rings, 25 mm) is suitable to achieve 97% of ammonia removal. Diameter of the absorber is the same with that of the stripper, and the required packing height is 2.1 m (packing: ceramic raschig rings, 25 mm).