Methane production from cattle manure supplemented with crude glycerin from the biodiesel industry in CSTR and IBR

The aim of the present research work was to optimise biogas production from cattle manure by adding crude glycerin from the biodiesel industry. For this purpose, 6% v/v crude glycerin (the optimum amount according to previous research) was added to ground manure and the mixture was sonicated to enhance biodegradability prior to anaerobic co-digestion at 55 °C. Two different reactors were used: continuously stirred (CSTR) and induced bed (IBR). The methanol and pure glycerin contents of the crude glycerin used in this study were 5.6% and 49.4% (w/w), respectively. The best results when operating in CSTR were obtained for an organic loading rate (OLR) of 5.4 kg COD/m3 day, obtaining 53.2 m3 biogas/t wet waste and 80.7% COD removal. When operating in IBR, the best results were obtained for an OLR of 6.44 kg COD/m3 day, obtaining 89.6% COD removal and a biogas production of 56.5 m3/t wet waste.

► Biogas production of cattle manure was optimised by adding glycerin as co-substrate. ► Better results using induced bed reactor versus continuously stirred tank reactor. ► Optimum organic loading rate was 6.4 kg COD/m3 day in inducted bed reactor. ► Ninety percent COD removal and 0.59 m3 CH4/kg VS (56.5 m3/t waste) were achieved.