A novel two-stage process for biological conversion of syngas to biomethane

This study shows biomethane production in a novel two-stage syngas biomethanation consisting of the thermophilic anaerobic digestion of sewage sludge combined with an injection of syngas as the first stage. Since the syngas does not contain enough reducing equivalents, the produced biogas was connected to the second stage consisting of the trickle-bed reactor with the external H₂ addition (ex-situ) to increase the CH₄ content further. The aim was to evaluate the influence of different syngas compositions on the biomethane production in both stages. The results showed that H₂ concentration in syngas is the main factor affecting the CH₄ content in biogas. Moreover, the ex-situ reactor with H₂ addition served to convert the residual CO and CO₂, achieving the maximum CH₄ content of 94.7% in the produced biomethane. In summary, the two-stage process enables biomethane production without any inhibitory effects on anaerobic sludge digestion.