PT  - JOURNAL ARTICLE
AU  - Gustavo Mockaitis
AU  - Guillaume Bruant
AU  - Eugenio Foresti
AU  - Marcelo Zaiat
AU  - Serge R. Guiot
TI  - Effect of Inoculum Pretreatment on Alcohol Production from Volatile Fatty Acids through an Anaerobic Solventogenic Process
AID  - 10.1101/2021.03.23.436570
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.03.23.436570
4099  - http://biorxiv.org/content/early/2021/04/05/2021.03.23.436570.short
4100  - http://biorxiv.org/content/early/2021/04/05/2021.03.23.436570.full
AB  - Background Production of alcohols from wastes through biological processes is environmentally and economically interesting, since they can be valorized as drop-in liquid fuels, which have a high market value. Using microbial mixed cultures in such processes is of great interest since it confers more stability, a higher resistance to both toxicity and contamination, and an increased substrate flexibility. However, there is still a lack of fundamental knowledge on such microbial populations used as inoculum in solventogenic processes. This work evaluates the effect of four different physicochemical pretreatments (acidic, thermal, acidic-thermal and thermal-acidic) on an anaerobic inoculum used for alcohols production from volatile fatty acids.Results All experiments were conducted in single batches using acetate and butyrate as substrates, at 30°C and with a pressurized headspace of pure H2 at 2.15 atm (218.2 MPa). Higher productions of both ethanol and butanol were achieved with both thermal and acidic-thermal pretreatments of the inoculum. The highest concentrations of ethanol and butanol produced were respectively of 122 mg.L-1 and 97 mg.L-1 for the thermal pretreatment (after 710 hours), and of 87 mg.L-1 and 143 mg.L-1 for the acidic-thermal pretreatment (after 210 hours). Butyrate was consumed and acetate was produced in all assays. A mass balance study indicated that the inoculum provided part of the substrate. Thermodynamic data indicated that a high H2 partial pressure favored solventogenic metabolic pathways. Finally, sequencing data showed that both thermal and acidic-thermal pretreatments selected mainly the bacterial genera Pseudomonas, Brevundimonas and Clostridium.Conclusion The acidic-thermal pretreatment selected a bacterial community more adapted to the conversion of acetate and butyrate into ethanol and butanol, respectively. A higher production of ethanol was achieved with the thermal pretreatment, but at a slower rate. The thermal-acidic pretreatment was unstable, showing a huge variability between replicates. The acidic pretreatment showed the lowest alcohol production, almost negligible as compared to the control assay.Competing Interest StatementThe authors have declared no competing interest.STPStandard temperature and pressure (0° C and 1 atm)ppH2Partial H2 pressure (átm)R2Levenberg-Marquardt algorithm correlation coefficientTVSTotal volatile solids (mg L-1)OTUOperational taxonomic unitHPLCHigh performance liquid chromatographyPCRPolimerase chain reactionRDPRibossomal data projectVFAVolatile fatty acidHButButyrateHPropPropionateHAcAcetateBut(OH)ButanolProp(OH)PropanolEth(OH)EthanolConcentration in respect of time (mg L-1)Time (h)Initial time for exponential growth phase (h)Ending time for exponential growth phase (h)Time in which maximum production rate () is achieved (h)Maximum production rate (mg L-1 h-1)Maximum concentration (mg L-1)ΔGrVariation of Gibbs’ free energy at a given condition (kJ mol-1)ΔG°rVariation of Gibbs’ free energy at standard condition (kJ mol-1)ΔGFrVariation of Gibbs’ free energy at final experiment condition (kJ mol-1)ΔGIrVariation of Gibbs’ free energy at initial experiment condition (kJ mol-1)