Simple yet effective: Microbial and biotechnological benefits of rumen liquid addition to lignocellulose-degrading biogas plants

In biogas plants, lignocellulose-rich biomass (LCB) is particularly slowly degraded, causing high hydraulic retention times. This fact lowers the interests for such substrates. To enhance LCB-degradation, cattle rumen fluid, a highly active microbial resource accruing in the growing meat industry, might be used as a potential source for bioaugmentation. This study compares 0%, 20% and 40% rumen liquid in a batch anaerobic digestion approach. Moreover, it determines the biogas- and methane-potentials as well as degradation-speeds of corn straw, co-digested with cattle manure. It inspects microbial communities via marker-gene sequencing, qPCR and RNA-DGGE and draws attention on possible beneficial effects of rumen addition on the biogas-producing community. Bioaugmentation with 20% and 40% v/v rumen liquid accelerated methane yields by 5 and 6 days, respectively (i.e. reaching 90% of total methane production). It also enhanced LCB- as well as (hemi) cellulose-and volatile fatty acid degradation. These results are supported by increased abundances of bacteria, methanogens and anaerobic fungi in treatments with rumen liquid amendment, and point towards the persistence of specific rumen-borne microorganisms especially during the first phase of the experiment. The results suggest that rumen liquid addition is a promising strategy for enhanced and accelerated exploitation of LCB for biomethanisation.