Browsing by Author "Peces, Miriam"

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    Inhibitory mechanisms on dry anaerobic digestion: Ammonia, hydrogen and propionic acid relationship
    (Elsevier, 2023-02-28) Rocamora, Ildefonso; Wagland, Stuart T.; Hassard, Francis; Villa, Raffaella; Peces, Miriam; Simpson, Edmon W.; Fernández, Oliver; Bajón Fernández, Yadira
    Inhibitory pathways in dry anaerobic digestion are still understudied and current knowledge on wet processes cannot be easily transferred. This study forced instability in pilot-scale digesters by operating at short retention times (40 and 33 days) in order to understand inhibition pathways over long term operation (145 days). The first sign of inhibition at elevated total ammonia concentrations (8 g/l) was a headspace hydrogen level over the thermodynamic limit for propionic degradation, causing propionic accumulation. The combined inhibitory effect of propionic and ammonia accumulation resulted in further increased hydrogen partial pressures and n-butyric accumulation. The relative abundance of Methanosarcina increased while that of Methanoculleus decreased as digestion deteriorated. It was hypothesized that high ammonia, total solids and organic loading rate inhibited syntrophic acetate oxidisers, increasing their doubling time and resulting in its wash out, which in turn inhibited hydrogenotrophic methanogenesis and shifted the predominant methanogenic pathway towards acetoclastic methanogenesis at free ammonia over 1.5 g/l. C/N increases to 25 and 29 reduced inhibitors accumulation but did not avoid inhibition or the washout of syntrophic acetate oxidising bacteria.
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    Managing full-scale dry anaerobic digestion: semi-continuous and batch operation
    (Elsevier, 2022-07-09) Rocamora, Ildefonso; Wagland, Stuart T.; Rivas Casado, Monica; Hassard, Francis; Villa, Raffaella; Peces, Miriam; Simpson, Edmon W.; Fernández, Oliver; Bajón Fernández, Yadira
    Dry anaerobic digestion usually results in inhibitors accumulation, which can be solved by adapting operation. Multiple strategies targeting increased stability are implemented in full-scale, but impacts are poorly documented. Two full-scale dry AD plants treating organic fraction of municipal solid waste (OFMSW) were investigated: a semi-continuous plant with compost addition and a batch plant testing different percolate recirculation strategies and inoculum to substrate ratios. Regression tree analysis was used to evaluate the effect of these strategies on methane yields and inhibitors accumulation. Compost addition in the semi-continuous plant reduced volatile fatty acids content but dropped methane flow up to 10 % when compost constituted over 10.1 % in weight of the incoming feedstock. This reduction was linked to the limited availability of easily degradable material in the compost. In batch dry AD, methane yields increased as percolate recirculated raised up to a range of 182–197 m3 (0.342–0.363 m3/t of biomass mix). Recirculation of higher percolate volumes reduced methane production, probably linked to pile compaction and inhibitors accumulation. The ratio of OFMSW, digestate and woodchip (bulking agent) fed was determinant, and methane production was higher when digestate was over 43.1 %, waste between 45 % and 47.5 % and woodchip over 8.2 % in weight in as received basis. Woodchip influenced percolation through the pile and supported reduced total ammonia levels of 3.2 g/l when kept over 8.2 %, which raised to 5.2 g/l for lower values.
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    Supplementation strategies to control propionic acid accumulation resulting from ammonia inhibition in dry anaerobic digestion: osmoprotectants, activated carbon and trace elements
    (Elsevier, 2025-04-01) Rocamora, Ildefonso; Wagland, Stuart T.; Hassard, Francis; Villa, Raffaella; Peces, Miriam; Fotidis, Ioannis A.; Simpson, Edmon W.; Fernández, Oliver; Bajón Fernández, Yadira
    Propionic acid accumulation in anaerobic digestion is a common sign of inhibition at high ammonia levels. To mitigate accumulation three supplementations were tested: osmoprotectants, trace elements and activated carbon. Activated carbon and osmoprotectants (MgCl2) achieved a 28 % increase in methane yield and a 3-fold reduction in hydrogen partial pressure compared with the control. Trace elements supplementation increased methane formation by 18 % without preventing instability. No supplementation avoided propionic accumulation, although MgCl2 delayed it. Activated carbon and MgCl2 supported proliferation of strict hydrogenotrophs, increasing microbial redundance with expected positive impacts on process resilience. Evidence beyond previous studies on the role of retention time as a control parameter of versatile archaea's methanogenic pathway is also provided. As retention time is reduced, syntrophic acetate oxidising bacteria are washed out of the system, likely resulting from an increase in their doubling time with inhibitors accumulation, preventing hydrogenotrophic methanogenesis and supporting previous observations of Methanosarcina being forced to conduct acetoclastic methanogenesis. Longer retention times to accommodate longer doubling times or alleviation of inhibition with activated carbon and MgCl2 supported retention of syntrophic acetate oxidising bacteria, enabling strict hydrogenotrophic archaea to proliferate. These supplementations would allow operation of industrial scale ADs at shorter retention times and higher throughputs. Results suggest that osmoprotectants and activated carbon addition were linked to a reduction in archaea's osmotic pressure and enhanced direct interspecies transfer, respectively, leading to increased methane formation despite propionic levels.