What are three types of mixing systems used in anaerobic digesters?

The correct answer highlights three primary mixing systems used in anaerobic digesters: gas mixing, internal mixing, and external mixing.

Gas mixing involves using gas, typically biogas produced during the digestion process, to create bubbles that stir the contents of the digester. This helps to enhance the contact between microorganisms and organic matter, improving the efficiency of the digestion process.

Internal mixing refers to methods that involve mechanisms placed within the digester itself, such as mechanical agitators. These devices actively circulate the digester contents, ensuring uniformity in the temperature and substrate distribution, facilitating better microbial activity and digestion efficiency.

External mixing systems operate outside the digester and may involve pumping the digestate out for mixing and then returning it to the digester. This can be useful for larger systems or when specialized mixing equipment is needed to maintain optimal conditions for anaerobic digestion.

Each of these mixing types is crucial in ensuring that the anaerobic digestion process occurs effectively, thus enhancing biogas production and reducing the formation of scum or sediment within the digester.