Methane from CO₂: Influence of different CO₂ concentrations in the flush gas on the methane production in BMP tests

The influence of carbon dioxide (CO₂) in the headspace gas on the specific methane (CH₄) production of blank samples with just inoculum during Biochemical Methane Potential (BMP) tests was studied. The headspace of the bottles had been flushed with 15 different ratios of CO₂ and N₂ prior to incubation, while they were treated otherwise identically. The results revealed that the CH₄ yield increased linearly with higher ratio of CO₂ in the flush gas reaching a 30% higher yield at pure CO₂ relative to pure N₂ headspace conditions. However, a slightly distinct lag is noticeable during the initial phase of the degradation process at high ratios of CO₂, hypothesizing a reversible disturbance of the biocenosis. Further experiments and analyses need to be performed to elucidate the underlying mechanisms.