Thermochemical pretreatment and anaerobic digestion of dairy cow manure: Experimental and economic evaluation

The aim of this study was to assess technically and economically the application thermochemical pretreatment in the anaerobic digestion of dairy cow manure. After selecting the optimum substrate to inoculum (S/I) ratio in a preliminary BMP test, the following tests compared 20 different pretreatment conditions varying temperature (100 and 37 °C), exposure time (5 and 30 min and 12 and 24 h) and chemical doses (0.5, 2, 6 and 10% of HCl or NaOH). The highest value of maximum production rate was achieved at an S/I ratio of 0.25 g VSs g VSi−1. The major improvements of the methane potential were 23.6% with 10% of NaOH at 100 °C for 5 min and 20.6% with 2% of HCl at 37 °C. The technical-economic analysis showed that the implementation of neither thermal alkali nor thermal-acid pretreatment would be feasible and the conventional one-step anaerobic digestion outperforms both alternatives.