Design of Environmental Processes Laboratory, School of Chemical and Environmental Engineering, Technical University of Crete, 73100, Chania, Greece.
J Environ Manage. 2024 Jul;364:121385. doi: 10.1016/j.jenvman.2024.121385. Epub 2024 Jun 13.
Biosolids is a by-product of wastewater treatment that needs to be further processed. Traditional biosolids treatment and disposal technologies are inefficient under the current demanding standards. Thermochemical conversion technologies have been employed for biosolids management, with gasification being the most promising due to the production of syngas, a gaseous product that may be used for the production of energy or high-added-value substances through reforming reactions. Gasification is a complex thermochemical process; its performance and yield are strongly affected by the type of feedstock, but also by the system configuration and process conditions. Gasification usually takes place at temperatures between 700 and 1,200 °C, but it may also occur at lower temperatures (above 375 °C: supercritical water gasification) or at higher temperatures (above 3,000 °C: plasma gasification). The present review briefly presents the biosolids management practices, focusing on the gasification process and syngas treatment, while the state of the art in biosolids gasification is critically presented and discussed. A number of types of gasifiers (more frequently fluidized bed, but also fixed bed, rotary kiln, downdraft, etc.), gasifying agents, and operational conditions have been used for biosolids gasification. The key results of the study regarding biosolids gasification are: (i) the increase of temperature and equivalence ratio enhances the gasification performance, resulting in high syngas yield and quality, high cold gas efficiency, and low tar and char production; (ii) the calorific value of the obtained syngas tends to decrease with the increase of equivalence ratio; and (iii) the use of catalysts has been proven to substantially improve the gasification performance, compared to non-catalytic gasification. The proper selection of technical parameters determines the effectiveness of biosolids gasification, which is considered as a promising technology for the energy recovery from biosolids, so to upgrade wastewater treatment and improve environmental quality.
生物固体是废水处理的副产物，需要进一步处理。在当前苛刻的标准下，传统的生物固体处理和处置技术效率低下。热化学转化技术已被用于生物固体管理，其中气化由于生产合成气而最有前途，合成气是一种气态产物，可通过重整反应用于生产能源或高附加值物质。气化是一种复杂的热化学过程；其性能和产率受原料类型的强烈影响，但也受系统配置和工艺条件的影响。气化通常在 700 至 1200°C 的温度下进行，但也可能在较低的温度下（高于 375°C：超临界水气化）或在较高的温度下（高于 3000°C：等离子体气化）发生。本综述简要介绍了生物固体管理实践，重点介绍了气化过程和合成气处理，同时批判性地介绍和讨论了生物固体气化的最新技术。已经使用了多种类型的气化炉（更频繁的是流化床，但也有固定床、回转窑、下降管等）、气化剂和操作条件来进行生物固体气化。关于生物固体气化的关键研究结果是：（i）温度和当量比的增加提高了气化性能，导致高合成气产率和质量、高冷煤气效率和低焦油和炭的产生；（ii）所得合成气的热值随着当量比的增加而降低；（iii）与非催化气化相比，已证明使用催化剂可大大提高气化性能。适当选择技术参数决定了生物固体气化的有效性，生物固体气化被认为是从生物固体中回收能源的有前途的技术，因此可以升级废水处理并改善环境质量。
