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Inhibitions de la digestion anaérobie : dynamiques écologiques, indicateurs microbiens et stratégies de résistance. Cas du phénol et de l’azote ammoniacal

Abstract : Anaerobic digestion (AD) is based on a complex biological network forming a real ecosystem.Nevertheless, the balance of this ecosystem is subjected to various perturbations induced by inhibitory molecules. In order to increase the robustness of this bioprocess, a better understanding of the inhibition effects on the microbial ecosystem is now needed. New solutions are also expected to enhance the resistance of digesters facing perturbations. During this work, we characterized in detail the effect of total ammonia nitrogen (TAN) and phenol, two inhibitors regularly involved in industrial units’ disruptions, on the mesophilic AD of biowaste collected on a deconditioning platform.A first set of experiment, conducted in batch digesters aimed at studying the response of a microbial ecosystem collected on an industrial digester treating aerobic sludge, to different inhibition levels. Ten concentrations were assessed for each of the inhibitors (ranging from 0 up to 5 g/L of phenol and from 0 up to 50 g/L of TAN). Half-inhibiting concentrations (IC50) characterizing the resistance capacity of the inoculum, were determined: 1.5 g/L of phenol and 19.0 g/L of TAN. The impact of different inhibiting concentrations towards the microbial diversity was investigated with high throughput rRNA 16S sequencing. Results showed that the functional resistance of the ecosystem to highest inhibitors concentrations were associated with important rearrangements of the microbial diversity. Within methanogenic populations, increasing inhibiting concentrations of phenol and TAN led to the implantation of genus Methanoculleus at the expense of Methanosarcina. The composition of bacterial syntrophic populations was also altered by the presence of both inhibitors. While family Syntrophomonadaceae was predominant under non-inhibiting conditions, families Synergistaceae and Spirochaetaceae became more abundant in presence of phenol and TAN, respectively.During the second set of experiment, five support media (2 zeolites, 2 activated carbons andchitosan) were introduced in parallel within batch digesters, so as to assess their capacity to limit the inhibition exerted by a concentration corresponding to each of the IC50 previously determined. Under noninhibiting conditions, support materials neither influenced the performance nor the composition of the microbial ecosystem. With phenol, each of the support enhanced biogas production while accelerating this inhibitor degradation. Some of the populations, such as genus Methanosarcina, which were also present under non-inhibiting conditions, were preserved.Moreover, even though support media did not influence TAN concentration, both zeolites and one of the activa ed carbons alleviated its inhibition by favoring the implantation of new populations such as family Marinilabiaceae. Both zeolites also maintained genus Methanosarcina within the ecosystem.In order to assess how these results could be transposed to other reactor configurations; one zeolite and one activated carbon were introduced in parallel within semi-continuous digesters after a step-wise inhibition by phenol was applied. Results obtained in batch digesters were confirmed with digesters whose functioning is closer to industrial units.This work revealed correlations between anaerobic digestion performance and structuralmodifications within archaeal and bacterial community composition. Microbial indicators, specific to the level and to the type of inhibition were evidenced. These results provide new insights with a view to conduct an ecological management of the anaerobic digesters. Furthermore, support material addition showed promising results to counteract inhibitions associated with phenol and TAN.
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Simon Poirier. Inhibitions de la digestion anaérobie : dynamiques écologiques, indicateurs microbiens et stratégies de résistance. Cas du phénol et de l’azote ammoniacal. Ecologie, Environnement. Institut agronomique, vétérinaire et forestier de France, 2016. Français. ⟨NNT : 2016IAVF0001⟩. ⟨tel-03383726⟩

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