From conventional to adapted microbiomes: Promoting high short-chain fatty acid yields and productivities from agricultural waste

Microbial consortia play an essential role in anaerobic fermentation (AF) devoted to the production of short-chain fatty acids (SCFAs) from organic wastes. AF is usually performed by a conventional anaerobic microbiome (CM) sourced from anaerobic digestion reactors. During AF, the microbiome undergoes an adaptation period to the imposed operational conditions and substrate characteristics, leading to the bio-enrichment of certain microorganisms. This work compared the use of CM and a bio-enriched microbiome (BM) as inoculum for AF of agricultural wastes in continuous stirred tank reactors (CSTR) with hydraulic retention time (HRT) of 8 d. The novelty of this study lies in demonstrating that using a BM enhances the production rate of SCFAs when compared to CM. BM, composed of adapted microorganisms previously working at an HRT of 10 d, allowed the highest SCFAs productivity (1.97 g/L·d) and concentration (15.6 g/L). Bioconversion efficiencies achieved with BM and CM (60.1 % and 71.8 %, respectively) were among the highest reported in literature. Microbiome analysis revealed inoculum-driven changes in the microbial community. However, Clostridium and Megasphaera, which are involved in the hydrolysis and acidification steps of AF and are associated with acetic acid formation and chain elongation, predominated in all cases (up to 48 % of the microbial abundance within the total community). These results evidenced the feasibility of operating CSTRs at an HRT of 8 d with diverse inoculum sources to maintain exceptionally high SCFA productivity and bioconversion. The outcomes also highlighted the robustness of the microbial community, even under short HRT, providing a novel strategy for AF processes optimization.