# Recent Advances in Hydrothermal Oxidation Technology for Sludge Treatment
## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Treatment Method**} & \multirow{2}{*}{**Investment, Operating COST**} & \multirow{2}{*}{**Advantages**} & \multirow{2}{*}{**Disadvantages**} & \multicolumn{2}{c}{**Development Trend**} \\ \cline{5-6}  & & & & **China** & **Other Developed Countries** \\ \hline \multirow{5}{*}{Anaerobic Digestion} & \multirow{5}{*}{High, Medium} & High investment cost, requires rigorous as energy, reduces volume & High investment cost, requires rigorous management, specific requirements for sludge solid content & Mostly used in agricultural areas for small-scale treatment & Mainly used in some agricultural developed countries, such as the United States, Canada, France, etc. \\ \hline \multirow{5}{*}{Drying and Incineration} & \multirow{5}{*}{High, High} & High investment and operating cost, high treatment, high degree of volume reduction & Uses less frequently consuming, potential for secondary pollution & Mostly used in some countries with tight land facults (such as the Netherlands, Germany and other countries with high incineration rates) \\ \cline{1-1} \cline{3-6}  & & & High investment and operating costs, high energy consumption, potential for secondary pollution & Mostly used in some countries with tight land facults and the Netherlands, Germany and other countries with high incineration rates) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 1: Advantages of hydrothermal oxidation technology for sludge treatment. Researchers both domestically and internationally have conducted extensive studies on hydrothermal oxidation for sludge treatment. For example, [PERSON] et al. designed a Cu-Ce/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) catalyst to assist in wet oxidation of antibiotic-laden sludge, achieving a chemical oxygen demand (COD) removal rate of 81.2% and a volatile suspended solids (VSS) removal rate of 93.8%. The resulting carboxylic acids included acetic and propionic acids, which can serve as carbon sources [15]. Similarly, [PERSON] et al. applied wet oxidation technology to pharmaceutical sludge and found that the concentration of volatile fatty acids (including acetic, propionic, isobutyric, and isoamyl acids) increased to 4819 mg/L (mg/L in this paper is equivalent to mg/dm\({}^{3}\) in the SI standard) at a pH of 12.56. This suggests that optimizing wet oxidation can enhance the quality of the sludge solution as a potential carbon source [16]. These studies strongly indicate that HTO is a promising sludge treatment method characterized by its high efficiency, effective detoxification, and ability for resource recovery. In summary, HTO, as a novel sludge treatment method, has significant development potential. A thorough exploration of research advancements in hydrothermal oxidation for sludge treatment is crucial for promoting innovation and development in sludge management and achieving detoxification, volume reduction, and resource recovery. This study focuses on the following key aspects: firstly, the principles of HTO for sludge treatment; secondly, the control of temperature, time, and pressure in the HTO process, which has an impact on sludge treatment; thirdly, optimization strategies to improve the efficiency of HTO; fourthly, the optimization of reactors used in HTO; and lastly, the products generated from sludge after HTO and their related applications. The study summarizes these aspects and addresses the challenges faced in this field, as well as future research directions. This review provides a theoretical foundation for utilizing hydrothermal oxidation technology in sludge treatment, with the hope of achieving sustainable development in this area.