Effect of substrate concentrations on methane and hydrogen biogas production by anaerobic digestion of a cassava starch-based polymer

Abstract

This study aims to evaluate the two-phase anaerobic digestion process of a cassava starch-based polymer, determining the ideal organic load to obtain the best results in terms of removal of solids and production of methane and hydrogen. Two reactors were used: one with an agitation and mixing system for the acidogenic phase, and the other was a tubular reactor for the methanogenic phase, both with ascending flow and semi-continuous feeding, with the effluent from the acidogenic reactor conducted from the methanogenic reactor. The loads were defined as concentrations of 8, 10, 12, and 14 g L−1 (on a wet basis), having HRT of 5 days for the acidogenic reactor and 20 days for the methanogenic. The analysis of the results showed that the concentration of 10 g L−1 had the best results for hydrogen and methane production in acidogenic and methanogenic phases, presenting 19.9 mL gVS-1 and 249.1 mL gVS−1, respectively. This treatment also showed the highest levels of gases in the biogas (43.2 % hydrogen in the acidogenic phase, and 76.6 % methane in the methanogenic phase). In addition, it showed the highest volatile solid removal means, reaching 84.0 % in the methanogenic phase. Thus, the anaerobic biodigestion process in two phases for the degradation of the polymer based on cassava starch presents technical feasibility, with high methane and hydrogen production; and concentrations above 10 g L−1, under the test conditions, cause destabilization in the reactors by the great formation of volatile acids and consequent reduction in the stability of microbiological cultures.