Biogas production from different size fractions separated from solid waste and the accompanying changes in the community structure of methanogenic Archaea

Katarzyna Bernat, Magdalena Zielinska, Agnieszka Cydzik-Kwiatkowska, Irena Wojnowska-Baryla

University of Warmia and Mazury in Olsztyn, Department of Environmental Biotechnology, Słoneczna Str. 45G, 10-709 Olsztyn, Poland.

Abstract

There is a need to study the biogas production of waste substrates using routine tests because the characteristics of these substrates influence the kinetics of methane fermentation. In this study, biogas production from different size fractions of solid waste (0–20 mm, 20–40 mm, 20–80 mm, and 40–100 mm) was measured using a 90 days gas production test in mesophilic conditions. How the methanogenic community structure during fermentation corresponds to the chemical composition of the size fractions was determined.

Biogas production strongly negatively correlated with the biogas production rate constants (k_biogas) due to differences in the availability of organic substances. Microorganisms in the 20–80 mm size fraction produced the most biogas (252 ± 11 L/kg TS, k_biogas = 0.16 ± 0.04 day^-1), which had the highest methane content (ca. 50%), probably because this size fraction had the highest organics content and the most diverse microbial community. In this size fraction, Methanosarcinaceae (acetoclastic microorganisms) and Methanobacteriaceae (hydrogenotrophic microorganisms) were more abundant than in other fractions. The 0–20 mm size fraction produced the least amount of biogas (65 ± 8 L/kg TS); however, its k_biogas was the highest (0.32 ± 0.05 day^-1), suggesting that organic matter was easily accessible to the microorganisms. Although the 0–20 mm size fraction is considered to be a mineral fraction that can be used for recultivation, the results of this study suggest that this fraction should be processed first to avoid environmental contamination.

Keywords: Biogas production test; Solid waste; Size fractions; Anaerobic digestion; Microbial community changes.