Urea hydrolysis and recovery of nitrogen and phosphorous as MAP
from stale human urine |
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Authors: | LIU Zhigang ZHAO Qingliang WANG Kun LEE Duujong QIU Wei and WANG Jianfang |
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Institution: | 1. State Key Lab of Urban Water Resource and Environment SKLUWRE, School of Municipal & Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China 2. Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan 10617, China |
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Abstract: | Laboratory-scale tests for magnesium ammonium phosphate (MAP) precipitation following urea hydrolysis of human urine were conducted using orthogonal experiment design. The effects of initial pH, temperature and the volumetric ratios of stale urine to fresh urine, on urea hydrolysis in urine were studied to determine the final hydrolysis time to recover most nitrogen from separated human urine by MAP. With a volumetric ratio of stale to fresh urine >10% and at temperature of 20℃ and above, urea hydrolysis could be completed in two days. Alkaline pH inhibited urea hydrolysis progress. The final pHs were all around 9.0 following urine hydrolysis, while the suspension pH might act as an indicator to detect the start and extent of urea hydrolysis. Over 95% of ammonium nitrogen and over 85% of phosphorus from hydrolyzed urine as MAP precipitate were obtained using MgCl2·6H2O and Na2HPO4·12H2O as precipitation agents at pH 8.5, molar ratio of Mg2 :NH4 -N:PO43--P at (1.2--1.3):1:1, mixing speed of 120 r/min, and precipitation time and reaction time of 3 h and 15 min, respectively. The precipitate has a structure resembling pure MAP crystal. |
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Keywords: | urea hydrolysis human urine magnesium ammonium phosphate (MAP) ammonium-nitrogen (NH4 -N) phosphorus |
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