Hydrothermal carbonization (HTC) is an effective means of energizing high-water-content biomass that can be used to convert sewage sludge (SS) into hydrochar and reduce nitrogen content. To further reduce the emission of NO_x during the combustion of hydrochar and seek proper disposal method of liquid product, the mechanism of nitrogen conversion was studied in the range of 180–320 °C and 30–90 min. At 180–220 °C, 42.15–52.91% of the nitrogen in SS was transferred to liquid by hydrolysis of proteins and inorganic salts. At 240–280 °C, the nitrogen in hydrochar was mainly in the form of heterocyclic -N (quaternary-N, pyrrole-N, and pyridine-N). The concentration of NH₄⁺-N increased from 6.82 mg/L (180 °C) to 26.58 mg/L (280 °C) due to the enhancement of the deamination reaction. At 300–320 °C, pyrrole-N (from 15.92% to 9.38%) and pyridine-N (from 5.52% to 3.73%) in the hydrochar were converted to the more stable quaternary-N (from 0.31% to 4.28%). Meanwhile, the NH₄⁺-N and amino-N in the liquid decomposed into NH₃. Prolonging the carbonization time promoted the hydrolysis of proteins, the conversion of heterocyclic -N, and the production of NH₃. Under optimal reaction conditions (280 °C and 60 min), the nitrogen in the SS is converted to stable forms and the energy balance meets the requirements of circular-economy. The results show that temperature determines the nitrogen form and the carbonization time affects the nitrogen distribution. So HTC has the potential to reduce NO_x emissions from SS energy utilization processes.

水热碳化 (HTC) 是为高含水量生物质提供能量的有效手段，可用于将污水污泥 (SS) 转化为水炭并降低氮含量。_{为进一步减少水力炭燃烧过程中NOx}的排放，寻求液体产物的合适处理方法，研究了180​​~320℃、30~90 min的氮转化机理。在 180–220 °C 下，SS 中 42.15–52.91% 的氮通过蛋白质和无机盐的水解转移到液体中。在 240–280 °C 时，水炭中的氮主要以杂环-N（季-N、吡咯-N 和吡啶-N）的形式存在。_{NH 4} ⁺浓度由于脱氨反应的增强，-N 从 6.82 mg/L (180 °C) 增加到 26.58 mg/L (280 °C)。在 300–320 °C 下，水炭中的吡咯-N（从 15.92% 到 9.38%）和吡啶-N（从 5.52% 到 3.73%）转化为更稳定的季氮（从 0.31% 到 4.28%） . 同时，液体中的NH ₄ ⁺ -N和氨基-N分解为NH ₃。延长碳化时间促进蛋白质的水解、杂环-N的转化和NH _3的产生. 在最佳反应条件下（280 °C 和 60 分钟），SS 中的氮转化为稳定形式，能量平衡满足循环经济的要求。结果表明，温度决定了氮的形态，碳化时间影响了氮的分布。因此，HTC 有可能减少 SS 能源利用过程中的 NOx_排放。