The treatment of wastewater not only helps to alleviate the scarcity of water and environmental challenges but also generates a by-product called Municipal Sewage Sludge (MSS). The MSS is a high moisture precipitant with plentiful organic and inorganic components. However, some pollutants in MSS components and its high-water content complicate its valorization, and thus, special attention is required for its valorization. Hydrothermal treatments (HTs) can be applied to feedstocks with high moisture content without pre-drying. These processes are gaining more attention to processing MSS into fuels and value-added materials. This work systematically reviews the findings recently emerged from HTs of MSS. The related chemical reactions and the effect of reaction parameters are highlighted based on most recent works. The problems addressed and those not yet addressed are also discussed. Some suggestions are made for the plausible applications of end products with the aim to optimize the whole process. Finally, insight is given into the future of MSS HTs and the concerns that might be the focus of substantial studies.

废水处理不仅有助于减轻水的短缺和环境挑战，而且还会产生一种称为市政污水污泥（MSS）的副产品。MSS是具有大量有机和无机成分的高水分沉淀剂。但是，MSS组件中的某些污染物及其高水含量使其价值化变得复杂，因此，对其价位化需要特别注意。水热处理（HTs）可以用于含水量高的原料，而无需预先干燥。这些过程在将MSS加工成燃料和增值材料方面得到了越来越多的关注。这项工作系统地回顾了MSS HT最近出现的发现。根据最近的工作，突出了相关的化学反应和反应参数的影响。还讨论了已解决的问题和尚未解决的问题。针对最终产品的合理应用提出了一些建议，旨在优化整个过程。最后，深入了解了MSS HT的未来以及可能成为大量研究重点的问题。