Background: Recent research articles indicate that direct interspecies electron transfer (DIET) is an alternative metabolic route for methanogenic archaea that improves microbial methane productivity. It has been shown that multiple conductive materials such as biochar can be supplemented to anaerobic digesters to increase the rate of DIET. However, the industrial applicability, as well as the impact of such supplements on taxonomic profiles, has not been sufficiently assessed to date.
Results: Seven industrial anaerobic digesters were supplemented with biochar for one year. A positive effect was observed for the spectrum of organic acids as the concentration of acetic, propionic, and butyric acid decreased significantly. Quantification of the cofactor F420 using fluorescence microscopy showed a reduction in methanogenic archaea. 16S-rRNA gene amplicon sequencing showed a higher microbial diversity within biochar particles as well as an accumulation of secondary fermenters and halotolerant bacteria. Taxonomic profiles indicate microbial electroactivity, and show the frequent occurrence of Methanoculleus , which has not been described in this context before.
Conclusions: Our results shed light on the interplay between biochar particles and microbial communities in anaerobic digesters. Both the microbial diversity and the absolute frequency of the microorganisms involved were significantly changed between sludge samples and biochar particles. This is particularly important against the background of microbial process monitoring. In addition, it could be shown that biochar is suitable for reducing the content of inhibitory, volatile acids on an industrial scale.