Anaerobic co-digestion of swine manure and enzymatically hydrolyzed carcasses at two different biodigesters

This study evaluated the behavior of the anaerobic co-digestion of hydrolyzed swine carcasses and swine manure at different organic loading rates (OLRs) in two different biodigesters, a covered lagoon biodigester (CLB) and a continuous stirred tank reactor (CSTR). Initially, we determined the biochemical methane potentials (BMP) of the substrates, indicating their suitability for methane production. The OLR progression in the CSTR had increments of about 0.5 g_VS L⁻¹ day⁻¹ over five different operating phases (160 days). The best performance was obtained with an OLR of 2.09 g_VS L⁻¹ day⁻¹ and a methane productivity (MP) of 1.12 L_{N CH4} L_reactor⁻¹ day⁻¹. A high concentration of total ammonia nitrogen (TAN), mainly in the form of free ammonia (FA), resulted in inhibition of methanogenic activity, with volatile fatty acids (VFA) accumulating in the biodigester. In CLB, the OLR progressions were increased by approximately 0.08 g_VS L⁻¹ day⁻¹ per phase over nine phases (260 days), with the best performance in OLR of 0.63 g_VS L⁻¹ day⁻¹ and MP at 0.31 L_{N CH4} L_reactor⁻¹ day⁻¹. CLB was stable throughout most of the experiment, even at high OLRs. Despite the good MP, the CLB showed instability in the last two phases, resulting in a significant increase in pH and FA concentration. It can be concluded that the use of hydrolyzed swine carcasses in co-digestion with manure has a high potential for CH₄ production. Although the TAN and FA concentrations had significant effects on the process, the biodigesters performed satisfactorily at moderate OLR.