Use of Hydrothermal Treatment for Anaerobic Digestion of Dairy Manure: Process, Perspectives, and Challenges

Effective management of dairy manure is crucial for reducing environmental and public health risks. This waste material can serve as a viable source of bioenergy via anaerobic digestion. The recalcitrance of lignocellulosic fiber in manure presents challenges for its efficient conversion to methane. Hydrothermal pretreatment of manure fiber improves process performance by deconstructing the lignocellulosic structure. Low-temperature hydrothermal treatment (90–180 °C) of lignocellulosic biomass optimally enhances the AD process performance by limiting the formation of inhibitory compounds such as furfurals. The integration of an optimal hydrothermal pretreatment within an anaerobic digestion system can improve the homogeneity, miscibility, and digestibility of dairy manure, thereby enhancing biogas yield. This review examines the hydrothermal treatment of lignocellulosic biomass, with a focus on dairy manure, the water chemistry involved in pretreatment, relevant process parameters, and the challenges faced in anaerobic digestion.