Toward green and efficient pretreatment for waste activated sludge resourcization and valorization: A review

The resourcization and valorization of waste activated sludge through anaerobic digestion are vital for promoting sustainability. However, the majority of organic matter in sludge is hindered from release by extracellular polymeric substances and plasma membranes, requiring pretreatment to disrupt these structures and enhance effective bioconversion. More than 3000 literature studies on pretreatment technologies have been conducted over the past five years, but there remains a clear gap in the comprehensive understanding of state-of-the-art sludge pretreatment methods. This review presents recent advancements in sludge pretreatment, with a focus on the emerging application of radio frequency technology. We examine the principles and effectiveness of various pretreatment methods, while critically assessing their performance and energy efficiency. This review will enhance the understanding of pretreatment mechanisms, fill the gaps in Frontier technologies, and inspire future developments toward more sustainable sludge management protocols.