What is done with the residue left after methane production from cattle dung?

Used as manure.

The residue left after methane production from cattle dung, also known as biogas slurry, is commonly used as manure.

Biogas production from cattle dung involves anaerobic digestion, where microorganisms break down the organic matter in the dung and produce biogas, primarily methane. After the digestion process, the remaining residue, which is rich in nutrients, is separated from the biogas.

The digestate, or biogas slurry, is a valuable byproduct that can be used as a nutrient-rich organic fertilizer. It contains nitrogen, phosphorus, potassium, and other essential nutrients beneficial for plant growth. Farmers often apply the digestate to their fields as a natural fertilizer, which helps enhance soil fertility, improve crop yield, and promote sustainable agriculture practices.

Using the residue as manure completes the cycle of utilizing cattle dung for biogas production while also returning the nutrients back to the soil, closing the loop of nutrient recycling.

Therefore, the most common practice with the residue left after methane production from cattle dung is to use it as manure.