Anaerobic Co-Digestion of Swine Manure and Hydrolyzed Swine Carcasses at Two Different Biodigesters

Abstract

Abstract This study compared 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). The OLR progression in the CSTR had increments of about 0.5 gVS L-1 d-1 over five different operating phases (160 days). The best performance was obtained with an OLR of 2.09 gVS L-1 d-1 and a methane productivity (MP) of 1.12 LN CH4 Lreactor-1 d-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 was increased by approximately 0.08 gVS L-1 d-1 per phase over nine phases (260 days), with the best performance in OLR of 0.63 gVS L-1 d-1 and MP at 0.31 LN CH4 Lreactor-1 d-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, where a significant increase in pH and FA concentration was observed. 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 a significant effects on the process, the biodigesters performed satisfactorily.