Improvement of biogas production by fungal treatment during the conversion of agricultural biomass into energy and digestate

Abstract

In this PhD study, the advantage of highly-cellulolytic white-rot fungus Trametes versicolor and anaerobic rumen fungus Orpinomyces sp. was taken by aerobic pretreatment and bioaugmentation approaches in lignocellulose-based anaerobic digestion (AD) trials, respectively. Selected cereal crop materials (i.e. wheat, rye, barley, triticale) were harvested at different stages and subjected to AD with cow manure as the co-substrate. In all AD tests, early-harvested barley was found to be the highest methane-yielding crop material. Changes in the quantity of selected key functional enzyme groups responsible for lignocellulose degradation and biomethanation were further determined in AD using quantitative real time PCR (qPCR). 16S rRNA gene amplicon sequencing revealed a more diverse microbial community in fungal-treated anaerobic digesters. Comparatively more unique microbiome of biogas reactors upon fungal treatment synergistically affected VFA production, cellulose degradation and eventually methane yield in an affirmative way. Following the AD tests, anaerobic digestates were collected on crop-basis and composted. All compost piles exhibited same abiotic profiles. Based on 16S and 18S rRNA gene amplicon sequencing, similar predominant bacterial and fungal genera detected that were mostly composed of lignocellulose degraders. In the last step, each final compost product was amended to agricultural fields where the crops were planted, and changes in soil microbiome was monitored using 16S rRNA gene amplicon sequencing. Proteobacteria was the most abundant bacterial phylum; whereas a shift in the predominance from Actinobacteria to Acidobacteria was observed following the compost amendment. In addition, there was a remarkable increase in the relative abundance of Bacteroidetes upon compost amendment.