Characterization of digesters enriched with high concentrations of propionate and chicken litter in anaerobic digestion

Abstract

The process of anaerobic digestion (AD) involves four key metabolic steps: 1) hydrolysis, 2) acidogenesis, 3) acetogenesis, and 4) methanogenesis. These steps are driven by a complex network of microorganisms working in unison to fully break down organic compounds into biogas. Propionate serves as a crucial intermediate in anaerobic digestion, with about 20 % to 43 % of methane production stemming from its complete oxidation. High concentrations of propionate, exceeding 2 g L-1, can result from organic overloads, leading to the failure of methanogenic processes and process imbalances. This study aimed to characterize a digester under continuous mesophilic conditions (35 ± 5 °C), fed with chicken litter 3 % of total solids and gradual enrichments with 0.5, 0.8, 1.2, 1.4, 1.6, 1.8, 2.0, 6.0, 12.0, 18.0, and 24.0 g L-1 of sodium propionate, to analyze changes in microbial populations. The microbial consortium that developed exhibited tolerance to high propionate concentrations. To elucidate its role in the degradation of propionate, 18 DNA samples were taken at strategic points of the enrichment and subjected to bioinformatic analysis. This analysis revealed the presence of species that do not act in syntrophy and facilitate propionate degradation. Furthermore, there was a substantial 50 % increase in methanogenic archaea. The developed microbiome enabled the stable maintenance of anaerobic digestion, ensuring consistent methane production without inhibition of methanogenesis despite high propionate concentrations.