Hydrogen and Methane Production from Biowaste and Sewage Sludge by Two Phases Anaerobic Co-digestion

The two phases anaerobic codigestion of biowaste and sewage sludge is the key to implementing the integrated treatment approach of municipal wastewater and organic fraction of municipal solid waste. In addition to increasing the production of biogas, the joint treatment of biowaste and wastewater allows to obtain readily biodegradable carbon source, an additive promoter of the denitrification stages and biological phosphorous removal. In order to develop a two-phase anaerobic codigestion process optimized for hydrogen and methane production, implementable in a wastewater treatment plant (WWTP), in the present study a pilotscale experimental apparatus was used to verify the feasibility and performance of the process. The addition of small amounts (5 – 10 %) of H2 to rich CH4 biogas improves the quality of gas combustion while reducing CO2 emissions. The experimental test was carried out at pilot scale using two stirred reactors both maintained at thermophilic temperature and semi-continuously fed. Nor chemicals neither recirculation were used to control the pH in first phase. The study lasted 50 days in which there were no evidences of any instability in the process. It was confirmed the possibility to obtain a stable hydrogen production with a specific hydrogen production of 40 L per kgTVS fed and a specific methane production in the second phase of 320 L per kgTVS fed. The biogas produced has a composition characterized by a stable presence of hydrogen over 5 %.