Optimizing anaerobic digestion by selection of the immobilizing surface for enhanced methane production

Maximizing methane production while maintaining an appreciable level of process stability is a crucial challenge in the anaerobic digestion industry. In this study, the role of six parameters: the type of immobilizing supports, loading rate, inoculum levels, C:N ratio, trace nutrients concentrations and mixing rate, on methane production were investigated under thermophilic conditions (55 ± 1 °C) with synthetic substrate medium. The immobilizing supports were Silica gel, Sand, Molecular Sieve and Dowex Marathon beads. A Taguchi Design of Experiment (DOE) methodology was employed to determine the effects of different parameters using an L16 orthogonal array. Overall, immobilizing supports influenced methane production substantially (contributing 61.3% of the observed variation in methane yield) followed by loading rate and inoculum which had comparable influence (17.9% and 17.7% respectively). Optimization improved methane production by 153% (from 183 to 463 ml CH4 l−1 d−1).

► The type of immobilizing support contributed over 60% variation in methane yield. ► Loading rate and inoculum each had an 18% contribution to methane yield. ► C:N ratio, mixing and trace nutrients had significant interactive effects. ► Optimization improved methane production by over 150%.