The influence of energy crop substrates on the mass-flow analysis and the residual methane potential at a rural anaerobic digestion plant

In a full scale anaerobic digestion plant exclusively operating on solid energy crops the mass-flows were analysed for two different substrate compositions over 583 d. The mono-fermentation of maize whole crop silage was compared to a mixture of maize and grass + clover silage. The two stage system required the input of dilution liquid guarantee digestion and agitation in the high loaded first stage (OLR: 5.50 kg_VS·m⁻³·d⁻¹). Grass + clover demanded the double mass of process dilution liquid, which reduced SRT from 65 d to 34 d for each stage and leaded to an increased generation of Solid Digestion Residues by separation. Experiments showed that 70% of the Residual Methane Potential are caused by the 7% mass fraction of SDR. For maize and maize + grass + clover RMPs of 6.34% and 11.80% were observed, respectively. RMP can also be expressed as additional substrate input required for full granted operation. Thus, the mass stream analysis is used to determine mitigation strategies for RMP.