Waste activated sludge (WAS) generated from wastewater treatment plants presents a significant environmental challenge due to its complex composition and disposal difficulties. In response, various strategies have been explored to manage sludge effectively, with renewable energy generation, particularly biomethane production via anaerobic digestion (AD), emerging as a promising solution. However, the hydrolysis stage, bottleneck in AD, hindering the degradation of complex organic molecules within WAS, necessitates innovative approaches. Chemical pretreatment methods have garnered attention for enhancing biomethane production efficiency. This review systematically assesses the efficacy of various chemical pretreatment approaches on WAS, examining their impacts on sludge composition, AD performance, and underlying mechanisms. Notably, the review underscores the influence of WAS characteristics, emphasizing the critical roles of dosage and pH in chemical pretreatment process. Moreover, it elucidates the synergistic potential of integrating chemical pretreatment with mechanical or biological methods, resulting in improved sludge degradability and enhanced biomethane yield. Additionally, the review emphasizes the importance of considering the characteristics and origins of sludge when selecting appropriate chemical pretreatment agents to optimize biomethane production. Furthermore, it highlights the potential benefits of implementing eco-friendly chemical pretreatment methods, which can mitigate the challenges faced by traditional chemical pretreatment approaches. © 2024 Elsevier Ltd
