Supercritical water gasification (SCWG) is considered a promising technology for sewage sludge (SS) treatment and utilization; however, char produced by a side reaction has become a bottleneck in SCWG. In this study, SS and its model compound (10% humic acid) were treated in an autoclave by SCWG at 400 °C for 30 min and by hydrothermal carbonization (HTC) at 250 °C for 300 min. The char yield was 15.4% in SCWG and 41.3% in HTC. The chars were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller (BET) analysis, and elemental analysis. By comparing the properties the char produced by SCWG and the hydrochar produced by HTC, which has been considered a valuable product, the feasibility of using char as an additional product in SCWG was explored. Compared with the char produced by HTC, the char generated in SCWG exhibits a lower BET specific surface area (8.257 and 15.782 m²/g) and combustion activity, a higher proportion of small pores (with pore sizes of 1–2 nm), and greater thermal stability. The formation pathway of the two types of chars is related to both dehydration and aromatization; decarboxylation also occurs in char formation during SCWG. Humus was proved to be related to char formation during the SCWG of SS based on experimental results obtained with the model compound. This work provides insights needed to guide follow-up treatments or utilization of the char produced during the SCWG of SS.

超临界水气化（SCWG）被认为是污水污泥（SS）处理和利用的有前途的技术；但是，副反应产生的炭已成为SCWG的瓶颈。在这项研究中，将SS及其模型化合物（10％腐殖酸）在高压釜中通过SCWG在400°C下处理30分钟，并在250°C下通过水热碳化（HTC）处理300分钟。SCWG中的炭产率为15.4％，HTC中的炭产率为41.3％。通过扫描电子显微镜，傅立叶变换红外光谱，热重分析，Brunauer-Emmett-Teller（BET）分析和元素分析对焦炭进行表征。通过比较SCWG生产的焦炭和HTC生产的水焦炭的性能（被认为是有价值的产品），探讨了在SCWG中使用炭作为附加产品的可行性。² / g）和燃烧活性，较小比例的小孔（孔径为1-2 nm）和更高的热稳定性。两种炭的形成途径与脱水和芳构化有关。SCWG期间在焦炭形成过程中也会发生脱羧。根据模型化合物获得的实验结果，证明腐殖质与SS的SCWG期间的炭形成有关。这项工作提供了必要的见解，以指导后续处理或SS的SCWG期间产生的炭的利用。