Department of Civil Engineering, Indian Institute of Science, 560012, Bengaluru, India.
Department of Biotechnology, National Institute of Technology Andhra Pradesh, Andhra Pradesh, 534101, Tadepalligudem, India.
Environ Sci Pollut Res Int. 2021 Apr;28(16):19901-19910. doi: 10.1007/s11356-020-11991-7. Epub 2021 Jan 6.
Studies on urea transformation reactions in blackwater are limited as urea rapidly hydrolyses under anaerobic condition. Since ammonium content of blackwater mainly originates from urine-urea, studying urea hydrolysis reactions is important to predict potential nitrate loads in aquifers from on-site sanitation facilities. In this study, urea spiked blackwater samples from pour flush pit toilet are used to examine the urea-ammonium pathways at varying initial urea concentrations and temperature. Based on laboratory results, the annual nitrate load imposed by the urea constituent of blackwater in a hard rock aquifer is predicted. Laboratory results illustrated that experimental temperature of 37 °C and pH range of 6.7 to 8.1 facilitated optimum urease enzyme activity at the initial substrate concentration of 500 mg/L. The Q value for urea transformation reactions indicated that increase in temperature has positive influence on enzyme activity. The reduction in urea concentration with time followed first-order kinetics. Part of ammonium ions in blackwater oxidises as nitrate ions that travel to the aquifer. Upon mixing and dilution, the nitrate concentration in 1 km of hard rock aquifer would annually increase by 0.004 mg/L due to blackwater infiltration from single household pour flush toilet.
关于黑水（厕所污水）中尿素转化反应的研究有限，因为在厌氧条件下尿素会迅速水解。由于黑水的氨氮含量主要来自尿液中的尿素，因此研究尿素水解反应对于预测现场卫生设施对含水层中潜在硝酸盐负荷非常重要。在这项研究中，使用来自冲落式厕所的添加尿素的黑水样本，在不同初始尿素浓度和温度下考察尿素-氨氮途径。基于实验室结果，预测了硬岩含水层中黑水尿素成分造成的年硝酸盐负荷。实验室结果表明，实验温度为 37°C，pH 值为 6.7 至 8.1，在初始底物浓度为 500mg/L 时有利于脲酶的最佳酶活性。尿素转化反应的 Q 值表明，温度升高对酶活性有积极影响。随着时间的推移，尿素浓度呈一级动力学降低。部分黑水中的氨氮离子会氧化为硝酸盐离子，这些硝酸盐离子会迁移到含水层中。由于单个家庭的冲落式厕所污水渗透，在 1 公里长的硬岩含水层中，混合和稀释后，硝酸盐浓度每年将增加 0.004 毫克/升。
