Experiment Research On Source-separated Urine Using Two Pretreatment Processes

Conquering long-term space flight and completing the Space Station is the main challenge for our future missions. To accomplish this task, a wastewater reclamation system must be developed to recover water. In space wastewater treatment, processing urine is still a challenge to present technologies. Presently, the research in this field is still in infancy. In terms of the existing problems in urine pretreatment, aimed at the practical problems existing in the urine pretreatment, the original treatment process was improved by the new pretreatment stabilizer and the electric-catalytic oxidation technique. The optimal parameters of two methods were explored by experiment, in order to provide important basis and references for the practical application.For the purpose of storage, the new pretreatment stabilizer was tested to determine the abilities to control solid precipitation, maintain constant pH, prevent microbiological replication and store easily. Meanwhile, the citric acid was determined to maintain pH in urine containing the new pretreatment stabilizer. The optimal parameters for using of the new pretreatment stabilizer and the citric acid were determined through experiments with a duration of7days: the dosing of the new pretreatment stabilizer and the citric acid were0.8g/L and1.0g/L, respectively. The addition of pretreatment agents was carried out concomitantly with the citric acids.The pretreatment of urine was conducted based on electric-catalytic oxidation. As the major components, ammonia and urea were used to investigate the electric-catalytic oxidation mechanism. Through single factor analysis with synthetic urine, the optimal parameters of electric-catalytic oxidation were presented as follows, Ti/RuO2/IrO2anode; Ti cathode; current density,50mA/cm2; electrode gap1cm; initial pH, about7; without stirring and NaCl.99.97%of the NH3-N,94.79%of TN and82.72%of TOC in the real urine were removed after electrolysis for3hours under this condition. According to the requirements for application, the electric-catalytic oxidation pretreatment was also conducted in sealed reactor to investigate its capability to store urine. The removal rates of NH3-N, TN, TOC and the color could be reached99.97%,94.79%,84.17%and100%, respectively. Moreover, the urine properties were not altered in the storage period.According to the particularity in aerospace applications, the urine pretreatment stabilizer dosing system, the electric-catalytic oxidation system and the vapor compression distillation (VCD) system were designed and modified. Through the method of mathematical model of energy and cost accounting of launch, economic analysis compared with old pretreatment stabilizer was accomplished. Compared with old pretreatment stabilizer,70.4dollars/L of launching cost can be saved, besides, because without dosing SO42-, solid precipitation of CaSO4was avoid, heat loss was effectively reduced and energy utilization also be improved. Electric-catalytic oxidation can save110dollar/L, but it also consumed about0.0648kw hof power. In addition to reducing heat loss, it was of benefit to boiling heat transfer, so energy utilization can be further improved.