Bioproduction and applications of short-chain fatty acids from secondary sludge anaerobic fermentation: A critical review

Anaerobic fermentation of secondary sludge is a crucial bio-energy tactic for achieving stabilization, reduction, and resource utilization of secondary sludge in wastewater treatment plants. Short-chain fatty acids (SCFAs), the end product of anaerobic fermentation, have received substantial attention owing to shorter fermentation time, higher economic value, and broader application range. This review summarizes the composition and structure of secondary sludge, the main tactics for SCFAs accumulation, the metabolic pathway of anaerobes' participation in SCFAs production, and the impact of SCFAs composition from the fermented liquid on its subsequent application. It was found that the composition and structure of secondary sludge may limit its decomposition and impede SCFAs production. Diverse technologies adopted can promote SCFAs accumulation to some extent. It was concluded that the application of SCFAs derived from anaerobic fermentation of secondary sludge depends on its individual SCFAs composition. This review would help advance the SCFAs production and specific applications from anaerobic fermentation of secondary sludge.

Automated summary

Anaerobic fermentation of secondary sludge is crucial for stabilizing, reducing, and utilizing secondary sludge in wastewater treatment plants. Short-chain fatty acids (SCFAs), the end product of anaerobic fermentation, are receiving attention due to their shorter fermentation time, higher economic value, and broader application range. This review summarizes the composition and structure of secondary sludge, tactics for SCFAs accumulation, metabolic pathways of anaerobes in SCFAs production, and the impact of SCFAs composition on subsequent applications. The findings highlight the limitations of secondary sludge in terms of decomposition and SCFAs production, as well as technologies to promote SCFAs accumulation. The review emphasizes the importance of considering individual SCFAs composition for the application of SCFAs derived from anaerobic fermentation of secondary sludge.