Abstract:Low-carbon treatment and resource disposal of urban sludge is an important way for sewage treatment to achieve "zero-carbon" or even "negative-carbon" treatment. With increasing global attention to climate change and the proposal of China's dual-carbon goal, the exploration and application of new technologies for urban sludge resource treatment and disposal have become a bottleneck issue that needs to be addressed in the current sewage treatment industry. In this study, we systematically review the research status and development directions of efficient anaerobic digestion enhancement technologies of sewage sludge from three aspects: high solid content, cold area treatment, and stable sewage sludge operation. Regarding the low efficiency of anaerobic digestion of sewage sludge in cold areas due to geographic and climatic factors, we discuss the effects of various pretreatment methods, including microwave and ultrasonic pretreatment, acid-alkali pretreatment, oxidation pretreatment, the addition of conductive materials like biochar, and heat preservation, particularly using ground-source heat pump systems on anaerobic digestion of sewage sludge. We emphasize the impacts of calcium peroxide coupling freeze-thaw pretreatment and magnetic oil sludge-based biochar addition technologies on anaerobic digestion of sewage sludge in cold areas. We summarize the optimization of operating conditions, such as stirring intensity, organic loading, temperatures, and C/N ratios, as well as the design of a high-efficiency heat and mass transfer anaerobic reactor using computational fluid dynamics simulation to enhance the anaerobic digestion of sewage sludge with high solid content. Furthermore, we deeply analyze the mechanisms of anaerobic co-digestion of sewage sludge and other substrates, including food waste and agricultural wastes (pig manure, wheat straw, and cow dung), along with molecular weight substrate compounding technology to alleviate the inhibition of the system by intermediate products (volatile fatty acid and free ammonia), thereby maintaining the high stability of the anaerobic digestion systems. We describe the applicable technology and index systems facing different directions and clarify the heat and mass transfer mechanism of methane production in anaerobic digestion systems under various dimensions. Additionally, we propose the future optimization directions for anaerobic digestion technology from the perspectives of microbial ecology, innovative reactor design, intelligent control systems, and multi-energy complementary systems. Finally, we prospect the development and application of sewage sludge anaerobic digestion technology based on the characteristics of sewage sludge in China, hoping to provide a reference for the subsequent development of high-efficiency anaerobic digestion of sewage sludge in cold regions, focusing on high solid content and high stability. Close-