Biochemical pathways and kinetic determinants of methane production in the anaerobic digestion process
Anaerobic digestion (AD) is a microbial process in which organic matter is broken down by microbial communities in the absence of oxygen, producing biogas composed mainly of methane and carbon dioxide. The process proceeds through hydrolysis, acidogenesis, acetogenesis and methanogenesis, and methane is the main energy-rich component of the resulting gas. Methane production during AD is controlled by interactions among biochemical pathways, reaction kinetics and microbial activity. Although these aspects are commonly discussed separately, their interdependence largely determines process efficiency and stability. This review presents an integrated analy - sis of the biochemical and kinetic mechanisms governing methane formation, linking microbial metabolism with substrate conversion dynamics and process performance. Particular emphasis is placed on the relationship between hydrolysis, methanogenesis, methane accumulation kinetics and the factors limiting methane production, including substrate resistance to biodegradation, operating conditions, inhibition and inefficient electron transfer. The review also discusses current approaches for enhancing methane production by increasing substrate availability, supporting microbial cooperation and applying kinetic-based process optimisation. Its distinctive feature is the integration of biochemical pathways, kinetic interpretation and process-limiting factors into one coherent framework for analysing methane production. This approach may support the development of more efficient, stable and predictable anaerobic digestion systems.