Research on the hydrolysis of human urine using biological activated carbon and its application in bioregenerative life support system

The water and nitrogen recovery from human urine are the crucial issues for the water recycling in the bioregenerative life support system (BLSS). Most of the water in the urine could be recovered through physical/chemical methods, however the efficiency of recovering nitrogen remained unsatisfactory. In our previous work, immobilized urease catalysis followed by reduced pressure distillation has been utilized to purify the urine, and high recovery efficiency of both water and nitrogen has been gained. However, the source of the urease and the immobilization preparation method would limit its practical application. In this study, biological activated carbon (BAC) immobilizing urease-producing microorganisms was explored as the continuous provider of urease to hydrolyze urea existing in human urine. The batch experiment results illustrated that it is feasible to use BAC technology to hydrolyze urea in urine and the highest urea hydrolysis efficiency of 79.33% was gained in synthetic urine with the powder activated carbon dosage (PACD) of 100 g/L and the hydraulic retention time (HRT) of 5 d. Image results of scanning electron microscope and confocal laser scanning microscope presented that BAC succcessfully immobilized living bacteria, and 16S rRNA high throughput sequencing illustrated that the main urease-producing bacteria were genera of Bacillus, Sporosarcina, Pseudomonas and Paracoccus, and genera of Pseudomonas and Paracoccus possessed heterotrophic nitrification ability as well. A pilot-scale membrane biological reactor inoculated with urea-hydrolyzing BAC cultivated in batch experiment was applied to treat the crew's urine continuously inside an experimental facility for BLSS, and the urea hydrolysis efficiency could maintain at 99.84% during 203 d operation.