Online

DeCola, Amy Camille

Civil and Environmental Engineering

2023

M.S.

Anaerobic digestion provides many benefits, such as diverting organic waste from landfills, promoting nutrient recovery, reducing greenhouse gas emissions, and producing renewable energy. A complex community of microorganisms is responsible for the anaerobic digestion process that converts organic matter into biogas, a renewable energy source. The start-up phase of an anaerobic digester is considered a crucial point in solidifying the core microbial community that will ensure a stable anaerobic digester. A full-scale anaerobic digester that co-digests cow manure and pre-treated food waste from a hydrolysis tank was studied from start-up through stable performance in order to better understand the dynamics of the core microbial community, assess gene abundance, and relate population dynamics to operational parameters. The microbial community in the hydrolysis tank, which was operated at a low pH of 3.5 to 4.4, consisted of organisms known to ferment carbohydrates to acetate and lactate, such as those in the genera Lactobacillus, Prevotella, and Bifidobacterium. Genes for the Bifid shunt were abundant while genes for hydrogen production and ferredoxin production and consumption were absent, suggesting that fermentation likely did not result in H2 production. The methanogenic archaeal community in the anaerobic digester had a high relative abundance up to 25%. The inoculation of the digester had little impact on abundant organisms, as Methanoculleus and an unclassified Methanomicrobiales genera were highly abundant before and after inoculation, though the abundance of total methanogenic archaea decreased after inoculation. While some genes related to acetoclastic methanogenesis were present, two diagnostic genes of this pathway (ack and pta) were absent, suggesting that hydrogenotrophic methanogenesis was the primary route. The high abundance of genes involved in ferredoxin cycling and H2 generation suggest that bacteria in the digester were likely producing H2.