Partial nitritation of landfill leachate in a SBR prior to an anammox reactor : operation and modelling

Els lixiviats d'abocadors urbans són aigües residuals altament contaminades, que es caracteritzen per les elevades concentracions d'amoni i el baix contingut de matèria orgànica biodegradable. El tractament dels lixiviats a través dels processos de nitrificació-desnitrificació convencionals és costós a causa de la seva elevada demanda d'oxigen i la necessitat d'addició d'una font de carboni externa. En els darrers anys, la viabilitat del tractament d'aquest tipus d'afluents per un procés combinat de nitritació parcial-anammox ha estat demostrada. Aquesta tesi es centra en el tractament de lixiviats d'abocador a través d'un procés de nitritació parcial en SBR, com un pas preparatori per a un reactor anammox. Els resultats de l'estudi han demostrat la viabilitat d'aquesta tecnologia per al tractament de lixiviats d'abocador. El treball va evolucionar des d'una escala inicial de laboratori, on el procés va ser testat inicialment, a uns exitosos experiments d'operació a llarg termini a escala pilot. Finalment, la tesi també inclou el desenvolupament, calibració i validació d'un model matemàtic del procés, que té com a objectiu augmentar el coneixement del procés.Urban landfill leachate are highly contaminated wastewater, usually characterised by high ammonium concentrations and low biodegradable organic matter content. Treating leachate through conventional nitrification-denitrification processes is expensive due to its high oxygen demand and the requirement of a supplementary external carbon source. In recent years, the feasibility of treating such streams with a low C:N ratio by a combined partial nitritation-anammox process has been demonstrated. This thesis deals with the treatment of landfill leachate by a partial nitritation-SBR, as a preparative step for an anammox reactor. The results of the study have demonstrated the feasibility of this technology for the treatment of landfill leachate. The work evolved from initial lab-scale studies, where the process was first tested, to a successful long-term experiment at pilot-scale. In addition, the thesis also includes the development, calibration and validation of a mathematical model of the process, aiming at increasing process knowledge

Low Fermentation pH Is a Trigger to Alcohol Production, but a Killer to Chain Elongation

Gasification of organic wastes coupled to syngas fermentation allows the recovery of carbon in the form of commodity chemicals, such as carboxylates and biofuels. Acetogenic bacteria ferment syngas to mainly two-carbon compounds, although a few strains can also synthesize four-, and six-carbon molecules. In general, longer carbon chain products have a higher biotechnological (and commercial) value due to their higher energy content and their lower water solubility. However, de-novo synthesis of medium-chain products from syngas is quite uncommon in acetogenic bacteria. An alternative to de-novo synthesis is bioproduction of short-chain products (C2 and C4), and their subsequent elongation to C4, C6, or C8 through reversed β-oxidation metabolism. This two-step synergistic approach has been successfully applied for the production of up to C8 compounds, although the accumulation of alcohols in these mixed cultures remained below detection limits. The present work investigates the production of higher alcohols from syngas by open mixed cultures (OMC). A syngas-fermenting community was enriched from sludge of an anaerobic digester for a period of 109 days in a lab-scale reactor. At the end of this period, stable production of ethanol and butanol was obtained. C6 compounds were only transiently produced at the beginning of the enrichment phase, during which Clostridium kluyveri, a bacterium able to carry out carbon chain elongation, was detected in the community. Further experiments showed pH as a critical parameter to maintain chain elongation activity in the co-culture. Production of C6 compounds was recovered by preventing fermentation pH to decrease below pH 4.5–5. Finally, experiments showed maximal production of C6 compounds (0.8 g/L) and alcohols (1.7 g/L of ethanol, 1.1 g/L of butanol, and 0.6 g/L of hexanol) at pH 4.8. In conclusion, low fermentation pH is critical for the production of alcohols, although detrimental to C. kluyveri. Fine control of fermentation pH to final values around 4.8 could allow sustained production of higher alcoholsThe authors would like to thank the Spanish Ministry (BestEnergy, CTQ2011-23632 and Bescarbox, CTM2013-43454-R for its financial support in this study. LEQUIA and EcoAqua have been recognized as consolidated research groups by the Catalan Government (2014-SGR-1168 and 2014-SGR-0484). RG gratefully acknowledges support from Ghent University BOF postdoctoral fellowship (BOF15/PDO/068

Impact of formate on the growth and productivity of Clostridium ljungdahlii PETC and Clostridium carboxidivorans P7 grown on syngas

The current energy model based on fossil fuels is coming to an end due to the increase in global energy demand. Biofuels such as ethanol and butanol can be produced through the syngas fermentation by acetogenic bacteria. The present work hypothesizes that formate addition would positively impact kinetic parameters for growth and alcohol production in Clostridium ljungdahlii PETC and Clostridium carboxidivorans P7 by diminishing the need for reducing equivalents. Fermentation experiments were conducted using completely anaerobic batch cultures at different pH values and formate concentrations. PETC cultures were more tolerant to formate concentrations than P7, specially at pH 5.0 and 6.0. Complete growth inhibition of PETC occurred at sodium formate concentrations of 30.0 mM; however, no differences in growth rates were observed at pH 7.0 for the two strains. Incubation at formate concentrations lower than 2.0 mM resulted in increased growth rates for both strains. The most recognizable effects of formate addition on the fermentation products were the increase in the total carbon fixed into acids and alcohols at pH 5.0 and pH 6.0, as well as, a higher ethanol to total products ratio at pH 7.0. Taken all together, these results show the ability of acetogens to use formate diminishing the energy demand for growth, and enhancing strain productivityThe authors thank the Autonomous Government of Catalonia (Generalitat de Catalunya) (2013 FI-DGR) and the Spanish Ministry of Science and Innovation (Best-Energy, CTQ2011-23632, CTM2013-43454-R) for their financial support in this study. LEQUIA and IEA have been recognized as consolidated research groups by the Catalan Government (2014-SGR-1168 and 2014-SGR-2016). RG gratefully acknowledges support from Beatriu de Pinos fellowship (BP-2011-B) and FP7 Marie Curie Career Integration Grants (PCIG13-GA-2013-618593

Tècniques científiques integrades

Obrir fitxer "menu.html" per obrir el llibre-eActivitats de l'assignatura 'Tècniques científiques integrades II' dels diferents graus de la Facultat de Cièncie