# Recent Advances in Hydrothermal Oxidation Technology for Sludge Treatment
## 3 Conclusions and Prospect  
Hydrothermal oxidation technology shows remarkable promise in the field of sludge treatment. Current research indicates that this technology offers a highly potential solution to various sludge disposal challenges. On one hand, hydrothermal oxidation effectively achieves sludge reduction and harmless treatment. By conducting reactions under optimized conditions, it rapidly decomposes organic pollutants in the sludge and enhances dewatering performance, thereby addressing land occupation issues associated with sludge. The removal of harmful substances from the sludge also mitigates risks for subsequent disposal and utilization, transforming sludge from waste into useful materials--an essential consideration in today's increasingly strained land resources. On the other hand, resource recovery stands out as a significant advantage of hydrothermal oxidation in sludge treatment. The products recovered after treatment can be repurposed as building materials, carbon sources, or fertilizers, contributing to successful waste utilization and promoting resource recycling. However, hydrothermal oxidation technology is not without its challenges. Several issues remain: (1) Cost: The implementation costs of these emerging technologies are currently high, particularly for industrial applications, which require substantial investment in equipment and operational expenses, potentially limiting widespread adoption. (2) Technological maturity: Compared to traditional wastewater treatment technologies, hydrothermal oxidation is still in a developmental stage, lacking sufficient long-term industrial application data to support its broader use. (3) Byproduct management: During the HTO process, the addition of certain additives may lead to the formation of toxic intermediate products. Additionally, some catalysts contain heavy metals that can leach into the products due to losses during use. These byproducts can hinder the subsequent resource recovery and utilization of the treated sludge. In light of the future development of this research, several prospects and key areas of focus are proposed:  
(1) Achieving sludge self-catalysis: Given the excellent performance of CWO, future research should focus on developing new catalysts that promote the hydrothermal oxidation of sludge. Beyond enhancing the catalyst's function, it is also crucial to explore whether the catalyst can enable the sludge to self-catalyze during the CWO process. This would allow the sludge itself to promote the removal of harmful substances, such as organic pollutants and heavy metals. (2) Prediction, planning, and control of products: Developing precise techniques for detecting product composition, such as advancements in liquid and gas chromatography, is essential. Alternatively, new kinetic models can be designed to accurately analyze the treated products. Furthermore, when utilizing these products as resources, it is necessary to test relevant parameters to ensure they meet usage standards. For example, the concentration of heavy metals must remain below the acceptable thresholds. (3) Elimination of ammonia nitrogen: At present, there is a large amount of ammonia nitrogen in the liquid phase of sludge treated by hydrothermal oxidation process, so it is very important to solve the issue regarding the potential harm of ammonia nitrogen. Future efforts should focus on further eliminating ammonia nitrogen and potentially converting it into nitrogen gas. This would improve the safety of sludge treatment and enhance the decontamination process. (4) Improving sludge dewatering performance: While hydrothermal oxidation technology can improve sludge dewatering, the results are not yet optimal. Future research should investigate how to enhance the dewatering efficiency to achieve more effective sludge reduction. (5) Producing a single carboxylic acid: A key finding of this study is that hydrothermal treatment of sludge can produce various volatile fatty acids such as acetic acid and propionic acid, along with non-volatile acids like lactic acid.