Optimum Co‐Digestion Ratio of Cattle Manure and Manipueira in a Single‐Stage Anaerobic Digester for Biogas Production

Several studies have shown that it is necessary to use a two‐stage anaerobic reactor in biogas production with manipueira as a substrate. The objective of this study is to show the possibility of producing good quality biogas from a single‐stage anaerobic reactor using manipueira and cattle manure as substrates. Five scenarios of codigestion are simulated in five digesters with different manipueira/manure ratios. The only digester that has a good result is the digester that is fed with 75% of manipueira and 25% of cattle manure. Under these conditions, biogas is produced with an average methane concentration of 62% the hydraulic retention time of the codigestion process is 30 days. The other digesters show that an excess of manipueira acidifies the codigestion process; such acidification can result in the severe inhibition of methanogenesis because of the accumulation of volatile fatty acids. On the other hand, an excess of cattle manure results in mixtures with a high concentration of lignin, cellulose, and hemicellulose mixtures, which, negatively influences the growth rate of methanogenic bacteria. Thus, using manipueira as cosubstrate, it is possible to produce a high‐quality biogas in a single‐stage anaerobic reactor. For efficient biogas production from manipueira, usually a two‐stage digester is required, because acidification occurs, leading to the collapse of biogas production. However, the authors could show that in a single digester using cattle manure as a cosubstrate (25%), it is possible to produce good quality biogas (high concentration of CH4), avoiding acidification.