4. Conclusions
Feedstock CM above 20% resulted in TAN concentrations rising
above a critical threshold of 7 g N L1, above which VFA accumulation
occurred. Methanogenesis was completely inhibited at TAN
>9 g N L1. 14C isotope labelling showed the predominant methanogenic
pathway at high TAN was hydrogenotrophic. Reducing
the proportion of CM allowed recovery of a failing digester with a reversal to a predominantly acetoclastic pathway to methane
production at lower TAN concentrations. The low digestibility of
the mixed feedstock led to a rise in digestate TS and a reduction
in both specific and volumetric methane production.