Evaluation of poultry manure and goat cheese whey anaerobic co-digestion

Hen droppings (HD) and Goat Cheese Whey (GCW) are two difficult substrates to be treated by anaerobic digestion due to their characteristics; however, their co-digestion offers the possibility of successfully treating these substrates together. The goal of this study was to evaluate the anaerobic co-digestion of HD and GCW at laboratory scale in order to determine biogas potential and possible operational problems before extrapolating results to a full-scale biogas plant. The potential methane production of HD, GCW and a mixture of both substrates was studied in batch mode, whereas the co-digestion of the mixture of HD and GCW was also studied in semi-continuous mode in a continuously stirred tank reactor. Results showed that the addition of GCW to HD increased methane production compared to HD alone; however, GCW alone showed the highest methane potential. In semi-continuous mode, the mixture of GCW and HD showed high biogas and methane yields (582.0 +/- 29.5 L-biogas kg VS-1 and 381.2 +/- 19.0 L-CH4 kg VS-1, respectively), although intense foaming incidents occurred. The composition of both substrates is complementary for their co-digestion and it improved the energy yield of the process. However, the economic viability of a biogas plant of 30 kWe, designed for treating HD and GCW, would be economically feasible only with subsidies for the investment and in the low range of investment costs for small scale biogas plants.