Abstract The increasing levels of sewage sludge production demands research and development to introduce more commercially feasible options for reducing socio-economic and environmental problems associated with its current treatment. Sewage sludge may be processed to produce useful products or as a feedstock for energy generation. Initially, the characteristics of sewage sludge are discussed in terms of composition and the current options for its treatment with the associated environmental impacts. Processes to valorize sewage sludge are discussed, including heavy metal removal from sewage sludge, production of bio-char, production and use of activated carbon and use of sewage sludge combustion ash in cement and concrete. Thermochemical processes i.e., pyrolysis, co-pyrolysis and catalytic pyrolysis, also gasification and combustion for process intensification, energy and resource recovery from sewage sludge are then critically reviewed in detail. The pyrolysis of sewage sludge to produce a bio-oil is covered in relation to product bio-oil composition, reactor type and the use of catalysts. Gasification of sewage sludge focusses on the characteristics of the different available reactor types and the influence of a range of process parameters and catalysts on gas yield and composition. The selection and design of catalysts are of vital importance to enhance the selectivity of the selected thermochemical pyrolysis or gasification process. The catalysts used for sewage sludge treatment need more research to enable selectivity towards the targeted desired end-products along with optimization of parametric conditions and development of innovative reactor technologies. The combustion of sewage sludge is reviewed in terms of reactor technologies, flue gas cleaning systems and pollutant emissions. In addition, reactor technologies in terms of technological strength and market competitiveness with the particular application to sewage sludge are compared for the first time for thermochemical conversion. A critical comparison is made of the drying techniques, co-feedstocks and catalytic processes, reaction kinetics, reactor technologies, operating conditions to be optimized, removal of impurities, fuel properties, their constraints and required improvements. The emphasis of this review is to promote environmental sustainability for process intensification, energy and resource recovery from pyrolysis, gasification and combustion involving the use of catalysts.

中文翻译：

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污水污泥的热化学转化：批判性评论

摘要 随着污水污泥产量的增加，需要进行研究和开发，以引入更具商业可行性的选择，以减少与其当前处理相关的社会经济和环境问题。污水污泥可以加工成有用的产品或作为能源生产的原料。首先，讨论了污水污泥的组成和当前处理方法以及相关环境影响方面的特性。讨论了污水污泥增值的过程，包括从污水污泥中去除重金属、生产生物炭、生产和使用活性炭以及在水泥和混凝土中使用污水污泥燃烧灰。热化学过程，即热解、共热解和催化热解，此外，还详细审查了用于工艺强化的气化和燃烧、从污水污泥中回收能源和资源。污水污泥热解生产生物油的过程涉及产品生物油组成、反应器类型和催化剂的使用。污水污泥的气化侧重于不同可用反应器类型的特性以及一系列工艺参数和催化剂对气体产量和组成的影响。催化剂的选择和设计对于提高所选热化学热解或气化过程的选择性至关重要。用于污水污泥处理的催化剂需要更多的研究，以实现对目标所需最终产品的选择性以及参数条件的优化和创新反应器技术的开发。从反应器技术、烟气净化系统和污染物排放方面对污水污泥的燃烧进行了审查。此外，首次将反应器技术在技术实力和市场竞争力方面与污水污泥的特定应用进行了比较，以进行热化学转化。对干燥技术、共原料和催化过程、反应动力学、反应器技术、要优化的操作条件、杂质去除、燃料特性、它们的限制和所需的改进进行了重要比较。