The terminal stage of anaerobic digestion is the biological process of methanogenesis. Here, methanogens use the intermediate products of the preceding stages and convert them into methane, carbon dioxide, and water. These components make up the majority of the biogas emitted from the system. Methanogenesis is sensitive to both high and low pHs and occurs between pH 6.5 and pH 8.[25] The remaining, indigestible material the microbes cannot use and any dead bacterial remains constitute the digestate.
A simplified generic chemical equation for the overall processes outlined above is as follows: