Study of a biological process for the combined production of hydrogen and methane and injection into the gas grid.

The European Union is aiming for climate neutrality by 2050. And to lower emissions derived from the use of natural gas, proposed by 2030 to achieve the production of 35 bcm of biomethane from anaerobic digestion processes. An alternative version of the process has become popular in the scientific community due not only to the capacity to increase biomethane yield but also for the recovery of biohydrogen. Blending it at 2%-20% v/v with methane would preserve the ability to be injected into the gas grid for common use, thus leading to a reduction in emissions. The process is based on the use of a second upstream reactor to separate the specific parameters of acidogenic fermentation and methanogenic phase. This thesis investigates the application of the two stage anaerobic digestion (TSAD) process in the agricultural context, specifically evaluating agricultural residues as a readily available lignocellulosic substrate. Addressing challenges for process optimisation and continuous biohydrogen production, by testing several strategies reported in the literature, such as the use of pretreatment. And, evaluating in detail the fermentation at different hydraulic retention times of livestock effluents, such as manure, and vegetal residues. Managing to achieve by plant derivatives’ co-fermentation a continuous biohydrogen production, with 12.35 NmLH2/gVS. Lastly, concluding with an economic evaluation of the applicability of the process, based on the results obtained.