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Acidogenic fermentation of household solid waste: bacterial enrichment at controlled pH
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Edité par CCSD ; École des Mines d'Albi-Carmaux -
In order to reduce our dependency to petrochemical resources, valorizing household solid wastes by producing platform molecules such as volatile fatty acids (VFAs), is an interesting alternative. It is possible to produce and extract VFAs through solid state fermentation (leach-bed reactors). Moreover, the VFA-rich broth can be purified and separated with a membrane process (i.e. nanofiltration). Hence, this study aimed at evaluating the role of an adapted and enriched inoculum (acidogenic bacterial populations) at three different pH to assess the effect on population and fermentation pathways. For this purpose, reactors with a total volume of approximately 1000 mL were operated in batch mode in a series of three successive runs (Fig. 1b). Tests with (inoculated) and without (control) inoculation in first batch, were conducted in duplicates. Heat pre-treated wastewater treatment plant (WWTP) sludge was used as inoculum. The substrate was a reconstituted fermentable fraction of household solid wastes, including food and green wastes, papers and cardboard (Fig. 1a). The substrate (and inoculum) quantities were adjusted to obtain a total solids (TS) content of 5% and a substrate to inoculum ratio of 20 at the beginning of the runs. pH was controlled and regulated by using HCl (1 to 3 M) and NaOH (0.25 to 0.5 M) solutions. Three pH conditions were experimented: 4.5, 5.5 and 6.5. Concentrations of fermentation metabolites (such as VFAs, lactate, and ethanol) and gases were measured daily and when relative pressure was higher than 5 millibars, respectively. Samples were taken to analyse the evolution of the microbial populations in the reactors during the tests.
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