Characterizing Chemistry and Microbiomes During Continuous Anaerobic Codigestion of Organics and Cattle Manure Digestate

Abstract

We characterized chemical and microbial responses to changes in the carbon-to-nitrogen ratio (C:N) and organic loading rate (OLR) during anaerobic codigestion (ACoD) of cattle manure digestate mixed with industrial organics. C:Ns of 25 and 35, both operating at OLRs ≤ 4 gVS L-1 d-1, sustained methane production averages of 0.36 ± 0.03 L gVS-1 d-1 and 0.32 ± 0.05 L gVS-1 d-1, respectively, throughout a 15-day period. Using 16S rRNA high-throughput sequencing coupled with PICRUSt2, taxonomy and predicted gene abundances were mapped to the major ACoD stages. C:N (25, 35) and the OLR (2, 4 gVS L-1 d-1) had minimal impacts on community structure and function, with a slight but notable increase in acetoclastic methanogens and alpha/beta diversity (Shannon and Bray-Curtis) at C:N 35. The microbial composition data indicated potential souring before the chemical data. ACoD was unsustainable at C:N 35 and OLR 6.5 gVS L-1 d-1, which was revealed by low methane production and souring. Digester failure correlated with a shift from acetoclastic to hydrogenotrophic methanogens (Methanobacteriaceae) and increased acidogenesis, driven by Provetellaceae and Lachnospiraceae. Our findings demonstrate that timely microbiome monitoring can contribute to efficient and sustained ACoD operation, especially when variable organic feedstock composition and loading rates are the norm.