Semi-continuous anaerobic co-digestion of dairy manure, meat and bone meal and crude glycerol: Process performance and digestate valorization

Abstract

Abstract The objective of this study was to investigate the effects of the addition of meat and bone meal (MBM) and crude glycerol (CG) on the anaerobic digestion of dairy manure (DM) with respect to digestion performance and digestate fertilizer value. The anaerobic co-digestion of DM, MBM and CG was conducted in semi-continuous stirred tank reactors at 37 °C with organic loadings between 2.63 and 2.86 g volatile solids (gVS)/L·d. Run 1 was a control reactor, while in Runs 2 and 3, DM was co-digested with MBM at ratios of 3.0:1.0 and 1.0:1.0 (gVSDM:gVSMBM), respectively. In Run 4, DM and MBM were co-digested with CG at a ratio of 1.0:0.7:0.3 (gVSDM:gVSMBM:gVSCG). The results showed that methane yields were increased by 9.1% and 30.2% in Runs 2 and 3, respectively, compared to Run 1, while the highest methane yield (0.39 L/gVSadded·d) was obtained in Run 4. The co-digestion of DM with MBM increased the ammoniacal nitrogen in the digestate by 2.1- to 2.3-fold, while no significant difference was observed for phosphorus. Due to the overabundance of nutrients in soil, the recovery of phosphorus and nitrogen and the recycling of water are the best strategies to sustain anaerobic digestion via an environmentally friendly approach.