Optimization of anaerobic digestion of a mixture of Zea mays and Miscanthus sacchariflorus silages with various pig manure dosages

Digestion of crop silage (Zea mays L. and Miscanthus sacchariflorus) with 0%, 7.5%, 12.5% and 25% pig manure as co-substrate was performed in continuous stirred-tank reactors, for a constant hydraulic retention time of 45 d and organic load rate of 2.1 g L–1 d–1. A matrix of correlations between biogas/methane production and parameters of anaerobic digestion was created in order to estimate process stability. The values of the correlation coefficients indicated that the most stable anaerobic digestion was achieved using 7.5% and 12.5% pig manure. In contrast, the positive correlation between ammonium and volatile fatty acids (r = 0.8698, p < 0.001) at 25% pig manure showed process instability. Compared to crop silage alone, pig manure favored the production of biogas and methane; the highest production rates were obtained with 12.5% pig manure.

► Co-digestion of two crop silages with pig manure at constant HRT and OLR.
► Dosage of pig manure influence anaerobic digestion stability.
► Positive statistical correlation between ammonia and VFAs confirm process imbalance.
► Correlations matrix anaerobic digestion parameters can be a tool to control process.