Anaerobic Digestion Manure Conversion and Recycling

Manure production is currently growing with the demand of meat products. Manure is a nutrient-rich biomass containing carbon, nitrogen, sulfur and phosphorous compounds which can at the same time be useful as fertilizing agents and harmful as pollutants in large quantities. Nitrogen and phosphorous can pollute surface and groundwater, leading to algal blooms and damage to aquatic ecosystems, while carbon, nitrogen and sulfur can lead to atmospheric emissions which can be strongly odorous, dangerous for human health and act as greenhouse gases. Composting and anaerobic digestion are two ways to treat manure to reduce these impacts, but only anaerobic digestion can also recover the energy still contained in manure. This chapter shows the basis of anaerobic digestion with a focus on manure as biomass. The effect on the anaerobic digestion of manure composition, which can vary widely depending on livestock species and feedstock, is explored. The most common types of anaerobic digestion reactors are summarized, detailing their advantages and disadvantages. The operative parameters to check for and control in managing an anaerobic digestion reactor are analyzed thoroughly, examining their effect on the process and how they interact in a complex system. Finally, as biogas is a green energy source and methane is an important energy carrier, its production and characteristics are evaluated, with a special focus on manure anaerobic digestion.