Study On The Characteristics Of Nutrients Transformation And Recovery Technology In Human Urine

Sewage contains a large quantity of valuable nutrients such as nitrogen and phosphorus, of which urine is the main nutrients source. About 80% of nitrogen, 50% of phosphorus in sewage comes from urine. At present, urine is usually treated and discharged mixing with other components together in the sewage by the city sewage treatment plant. But this high cost of process ignored the recovery of nitrogen and phosphorus. Urine contains lots of nutrients with a very small volume in contrast with other wastewater, so the source -separation and treatment of urine as well as the recovery of nutrients from urine had been studied in this paper.This paper analyzed the characteristics of nitrogen and phosphorus transformation in human urine and discussed which factors affected the nutrients transformation. This study pointed that TN in urine is 8000-10000mg/L, and the most of which is urea. In urine the urea catalyzed by the free urease directly or the microorganism indirectly could be complete hydrolyzed and produce ammonia rapidly. But because there is not enough urease in the fresh urine, when no urease was added in the urine, the conversion of urine to ammonia was very slow, even after 20 days, the final conversion efficiency was 18.2%. This study also pointed that TP in urine is 700-2000mg/L, most of which is polyphosphate which can be transformed to phosphate quickly. Further more, temperature and pH also play important roles in urea hydrolisis and maintaining the stability of phosphate in urine. The conversion from urea to ammonia is an important step for the N- and P-recovery when using the struvite method. In order to increase the hydrolysis of urea, we added commercial urease, activated sludge (AS) and compost to the urine.This study added urease, AS and compost to the hydrolysis rate of urea. The results showed that the experiment was carried out in a temperature of 30℃, pH of 6.5 . However, when the urease was added in the urine, the hydrolysis rate was significantly increased, i.e., the ammonia conversion from urine were 25.4%,49.5% and 85.0%, respectively, after one day inoculation with the dosage of 10,20 and 50 mg/l. However, the function of urease seemed to be disabled after one-day innoculation, since no increase of ammonia was observed. The result of hydrolysis with the AS dosage of 10,20, and 50 g/L (based on dry sludge weight) and the inoculation method was the same as the experiment of urease. At the dosage of 10g/L, the ammonia concentration increased rapidly and reached the maximum concentration of approximately 7000mg/L in the first 6 days. For the dosage of 20 and 50g/L, it took 4 and 2 days to reach the maximum ammonia concentration, respectively. At the same condition, for the compost-dosage of 10, 20 and 50g/L, it took 14,10 and 5 days to reach the maximum ammonia concentration, respectively. This results show that the dosage of urease affected not only the speed of hydrolysis but also the maximum ammonia concentration while the dosage of AS and compost only affected the speed. So urea hydrolysis enhanced by AS is feasible in economic and technology.This paper followed MAP precipitation method with external P-source dosing to recover the N and P in the hydrolyzed urine. The hydrolyzed urine was filtered to remove the residual of AS and the nutrient in the filtrate was recovered using magnesium-ammonium-phosphate (MAP) precipitation by adding MgCl₂ and Na₂HPO₄. When [Mg]:[N]:[P] was 1.4:1:1 on a molar base and the pH was 10.5, the efficiency of N- and P-recovery was up to 95% and 98%, respectively . Using X-ray diffraction analysis, the main phase of precipitates was identified as NH₄MgPO₄·6H₂O comprised of 70% of the precipitate.