Metagenomics reveals microbiome changes with lignocellulose biomass addition in anaerobic co-digesters treating swine wastewater

Abstract

<b><sc>Abstract.</sc></b> Anaerobic co-digestion of animal wastewater and lignocellulosic biomass for biogas production allows for the simultaneous production of renewable energy and reduction of waste when organics present in waste are converted into methane and carbon dioxide. As process inefficiencies can limit the profitability of this technology, the addition of lignocellulosic biomass presents an opportunity to boost biogas production. In this study, we used corn stover or switchgrass as lignocellulosic biomass additives to the thermophilic anaerobic digestion of swine wastewater at different organic loading rates and compared performance to a control digester treating only swine wastewater. Biogas production rate increased significantly with the addition of the lignocellulosic biomass. However, there was not a significant increase in methane yield per gram of volatile solids (VS) added in the digesters at any of the loading rates tested (1.0-3.5% total solids). To address these inefficiencies, a metagenomics study using 16S rRNA amplicon sequencing was performed to investigate the digester microbiomes in order to better understand the hydrolysis of lignocellulosic biomass. Results from 16S amplicon sequencing showed that the addition of lignocellulosic biomass markedly changed the digester microbiome. When compared to the control digester, both co-digesters showed lower abundance of Proteobacteria and increased abundance of Spirochaetota and Firmicutes. Thermotogota was a dominant microbe in all digesters. Differential abundance analysis revealed a high number of differentially abundant microbes within Firmicutes and Chloroflexi, especially Class Clostridia. This identification of microbes potentially responsible for lignocellulose degradation will help in optimizing digester design and improve performance.