RT info:eu-repo/semantics/doctoralThesis
T1 Integral Valorisation of Food Waste through the Recovery of Biohydrogen & Methane
A1 Martínez Mendoza, Leonardo José
A2 Universidad de Valladolid. Escuela de Doctorado
K1 Medio Ambiente
K1 Dark Fermentation
K1 Fermentacion Oscura
K1 Bio-Hydrogen
K1 Bio-Hidrógeno
K1 Anaerobic Digestion
K1 Digestión Anaerobia
K1 Desechos de Frutas
K1 3308 Ingeniería y Tecnología del Medio Ambiente
AB The increasing generation of fruit and vegetable waste (FVW) poses a significant environmental, economic, and social challenge due to its high biodegradability and tendency to uncontrolled acidification. Despite being rich in organic matter, FVW is often underutilized, commonly ending up in landfills or incinerators, contributing to pollutant emissions and resource loss. In alignment with the Circular Bioeconomy Strategy and the 2030 Sustainable Development Goals, its valorization for renewable bioenergy production is a strategic priority.In this context, dark fermentation (DF) and anaerobic digestion (AD) emerge as key biotechnological processes for converting FVW into hydrogen (H2) and methane (CH4), respectively. However, DF faces several limitations, such as the accumulation of lactic acid (HLac), operational instability, and low reproducibility—especially under continuous operation. A promising alternative is lactate-driven dark fermentation (LDDF), which utilizes HLac as a fermentable intermediate rather than an inhibitor, allowing for more efficient and stable H2 production. Nevertheless, the effects of operational parameters such as pH, total solids (TS), biomass concentration, hydraulic retention time (HRT), and organic loading rate (OLR) on LDDF performance remain insufficiently understood.This thesis addresses these gaps by systematically evaluating these parameters in LDDF systems operated in both batch and continuous modes using FVW as substrate. Under mesophilic conditions, batch experiments showed that optimal H2 production was achieved at neutral pH (7.0), low TS (5%), and high inoculum concentration (1800 mg VSS/L), reaching a yield of 49.5 NmL H2/g VSFED and a maximum productivity of 976.4 mL H2/L-h. These conditions reduced HLac accumulation and favored the co-production of acetate and butyrate, highlighting a delicate balance among metabolic pathways and the importance of precise control of operating conditions.In continuous systems, progressive reduction of HRT from 24 to 6 hours (OLR of 47–188 g VS/L-d) revealed an optimal HRT of 9 hours, achieving an unprecedented H2 production rate of 11.8 NL H2/L-d and a yield of 95.6 NmL/g VSFED. These results underscore the critical role of residence time and confirm HLac as a key driver in DF performance.To further enhance energy recovery, conventional single-stage AD was compared with a two-stage system including a preliminary HLac-producing acidogenic phase. The two-stage configuration outperformed the single-stage system, with a 32% increase in CH4 productivity (959 NmL CH4/L-d) and a 36% increase in CH4 yield (398 NmL/g VSFED). Although both systems produced similar CH4 content and stability, the two-stage system achieved more efficient substrate conversion and greater microbial specialization, with Lactobacillus dominating the acidogenic phase and Methanobacterium and Methanothrix prevailing during methanogenesis.Reproducibility, a key factor for process scalability, was also addressed by operating parallel reactors under identical conditions through six experimental phases. A consistent H2 productivity of 6.7 ± 0.7 NL H2/L-d and stable profiles of organic acids were achieved, validating the robustness of LDDF under controlled conditions. Strategies such as bioaugmentation and nutrient supplementation led only to temporary improvements, indicating the need for long-term adaptive optimization approaches to mitigate biological variability.Overall, this research provides valuable scientific and technological insights for the optimization and integration of DF and AD in FVW valorization. The results demonstrate that, with proper adjustment, LDDF can serve as a reliable platform for H2 production, and that HLac-based two-stage AD offers a superior alternative for CH4 generation. From a comprehensive perspective, combining LDDF and AD enables the conversion of organic waste into two high-value biofuels— H2 and CH4—promoting resource recovery, circular economy principles, and climate change mitigation. The findings lay the groundwork for designing robust, scalable, and sustainable biorefineries capable of addressing current environmental and energy challenges through the efficient use of organic waste.
YR 2025
FD 2025
LK https://uvadoc.uva.es/handle/10324/80832
UL https://uvadoc.uva.es/handle/10324/80832
LA eng
NO Escuela de Doctorado
DS UVaDOC
RD 12-ene-2026