Estudio a escala piloto de la desulfuración anóxica de biogás empleando un efluente nitrificado a partir de lixiviados de vertedero
Biogas generated in landfills is a valuable source of renewable energy, the use of which is hindered by the presence of compounds that affect its quality, primarily hydrogen sulfide (H2S). This compound is corrosive and toxic, and its combustion generates sulfur oxides, necessitating its reduction or removal for most applications. Biological technologies offer a sustainable alternative to physicochemical methods, among which is anoxic desulfurization. However, this technology relies on electron acceptors such as nitrate/nitrite, which, if sourced from chemical reagents, increase process costs. Therefore, this Doctoral Thesis addresses this challenge from a circular economy perspective by proposing and validating a pilot-scale integrated system that couples two waste treatment processes: biogas purification and landfill leachate treatment. The study proposes using the nitrified effluent from ammonium-rich leachate as a low-cost source of nitrate/nitrite for anoxic biogas desulfurization, thereby reducing operational costs and facilitating the management of this complex waste stream. A key byproduct of the anoxic desulfurization process is elemental sulfur. This sulfur can be recovered from suspended-growth bioreactors for use as a fertilizer or as a raw material in the chemical industry. To optimize both the bioprocess and byproduct recovery, an analytical method was first developed and validated for the quantification of biogenic sulfur (S0) using gas chromatography with a pulsed flame photometric detector (GC-PFPD), combined with a simple sample preparation based on filtration and toluene extraction. This method exhibited an error of less than 5% when applied to samples from a laboratory-scale stirred-tank anoxic desulfurization bioreactor. Additionally, a recovery method for biogenic sulfur was optimized via coagulation-flocculation, achieving removal efficiencies exceeding 97% with a cationic flocculant at a dosage of 0.82 mg/L (0.5 mg flocculant per g S0) at a stirring speed of 30 rpm and a pH of 8.0. In subsequent tests with biogenic sulfur from biological samples with high solids and organic matter content, the required flocculant dosage increased 40 times (to 20 mg flocculant per g S0). To generate the low-cost electron acceptor, the nitrification of real landfill leachate was studied at a pilot scale in a 1 m3 sequencing batch reactor (SBR). Over the 61-week operational period, a total volume of 8,950 L of landfill leachate was treated, with an average ammonium concentration of 1,410±362 mg N-NH4+/L. The system demonstrated high robustness and resilience, with the reactor stably generating nitrate and removing over 83.9% of the ammonium under controlled pH (7.4±7.7) and temperature (25±27°C) conditions. A maximum ammonium elimination capacity o161 g N-NH4+/(m3·d) (at 99.9% efficiency) and a nitrate production rate of up to 95.4 g N-NO3-/(m3·d) were achieved. High leachate salinity was identified as a critical factor requiring control via dilution to prevent process inhibition. To assess the biomass's sensitivity to increasing leachate concentrations, its activity was evaluated through respirometric tests, and the data were fitted to a Haldane-type inhibition model. The maximum substrate oxidation rates obtained in these laboratory-scale tests were 8.89 mg N/(gVSS·h) for ammonium and 5.91 mg N/(gVSS·h) for nitrite. Finally, the integration of both processes was evaluated through the long-term operation of a pilot-scale (1 m3) anoxic bioscrubber system fed with real landfill biogas (total volume: 264,812 m3) and the nitrified effluent (total volume: 2.4 m3). The system demonstrated high stability, achieving H2S removal efficiencies exceeding 85% (with a maximum of 97%) under optimal conditions (pH 7.5±8.0 and T > 22°C). The system's operational limits were determined, reaching a maximum elimination capacity of 50.8 g S-H2S/(m3·h) with an elemental sulfur yield of 60%. Microbial community analysis revealed a predominance of the genus Thioalkalispira-Sulfurivermis as the primary driver of desulfurization in the bioreactor. The system proved resilient to operational disturbances, such as recirculation pump failures and fluctuations in the biogas flow rate. This study provides valuable insights into the practical application of anoxic bioscrubbers for landfill biogas biodesulfurization, highlighting key control factors and offering a foundation for enhancing the efficiency and sustainability of biogas purification technologies under real-world constraints.
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