Evaluating the effect of biochar addition on the anaerobic digestion of swine manure: application of Py-GC/MS

The anaerobic digestion process of swine manure was studied when char was used as supplement for improving performance. The use of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was proposed for assessing the organic matter degradation. The assessment on biogas production was carried out using samples of swine manure (SM) supplemented with char in one case and pre-treated by microwave irradiation in the other. This experimental set-up allows for the comparison of the biological degradation observed under these two different configurations and therefore aids in understanding the effect of char particles on the process. Results showed similar performance for both systems, with an average improvement of 39% being obtained in methane production when compared to the single digestion of SM. The analysis of digestate samples by Fourier transform infrared (FTIR) spectroscopy and Py-GC/MS showed improved degradation of proteins, with the Py-GC/MS technique also capable of identifying an increase in microbial-derived material when char was added, therefore highlighting the relevant role of carbon conductive particles on biological systems. Py-GC/MS along with the use of FTIR spectroscopy has proven to be useful tools when evaluating anaerobic digestion

Post-treatment of dewatered digested sewage sludge by thermophilic high-solid digestion for pasteurization with positive energy output

This study investigated the possibility to use thermophilic anaerobic high solid digestion of dewatered digested sewage sludge (DDS) at a wastewater treatment plant (WWTP) as a measure to increase total methane yield, achieve pasteurization and reduce risk for methane emissions during storage of the digestate. A pilot-scale plug-flow reactor was used to mimic thermophilic post-treatment of DDS from a WWTP in Linkoping, Sweden. Process operation was evaluated with respect to biogas process performance, using both chemical and microbiological parameters. Initially, the process showed disturbance, with low methane yields and high volatile fatty acid (VFA) accumulation. However, after initiation of digestate recirculation performance improved and the specific methane production reached 46 mL CH4/g VS. Plug flow conditions were assessed with lithium chloride and the hydraulic retention time (HRT) was determined to be 19-29 days, sufficient to reach successful pasteurization. Degradation rate of raw protein was high and resulted in ammonia-nitrogen levels of up to 2.0 g/L and a 30% lower protein content in the digestate as compared to DDS. Microbial analysis suggested a shift in the methane producing pathway, with dominance of syntrophic acetate oxidation and the candidate methanogen family WSA2 by the end of the experiment. Energy balance calculations based on annual DDS production of 10 000 ton/year showed that introduction of high-solid digestion as a post-treatment and pasteurization method would result in a positive energy output of 340 MWh/year. Post-digestion of DDS also decreased residual methane potential (RMP) by >96% compared with fresh DDS. (C) 2020 The Authors. Published by Elsevier Ltd