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. • Bio-enriched microbiome promoted high SCFAs yields and production rates. • Both inocula led bioconversion ranking among the highest reported in literature. • Inocula had stronger impact on microbiome and SCFA profile than HRT reduction. • Acetic and butyric were the predominant acids in all tested conditions. • Conventional microbiome promoted chain elongation into valeric and caproic acids.