Impact of waste origin and post-treatment techniques on the composition and toxicity of biogas

The toxicity of real biogas on human lung cells exposed at the air-liquid interface (ALI) was studied for the first time. Real biogases were sampled on site at two biomethanation centers, one in France and the other in Lebanon. Biogas was produced from the organic component of household municipal waste (i.e., food/kitchen waste and green waste). The chemical analysis was performed by Gas Chromatography (GC) or by online analyzers, in situ or further after collection of the samples in Tedlar bags or adsorption on Tenax tubes. The real biogases were composed of CH₄ and CO₂, NH₃, H₂S, and of some Volatile Organic Compounds, such as BTEX and terpenes. The main biogas components from the two selected biogas plants were closed due to the use of the same Valorga® process, whereas the concentrations of the secondary compounds depended on the origin and nature of waste and on the use of a biogas post-treatment. Green waste produced higher concentrations of terpenes. Moreover, the treatment by desulfurization and by activated charcoal decreased its content in sulfur compounds and BTEX, respectively. Then, the toxicity of the two biogases was investigated by RT-qPCR in human lung cell cultures (BEAS-2B) exposed using the ALI Vitrocell® exposure device. No cytotoxicity was detected in the exposed cells. A dose- and time-dependent induction of inflammation markers was observed at the gene level in relation to oxidative stress in BEAS-2B cells exposed to both biogases. These inductions were mainly higher after exposure to the biogas containing more secondary compounds, such as BTEX. In conclusion, this in vitro mechanistic study confirmed the importance of the post-treatment of the biogas to lower the concentration of secondary compounds. Indeed, elimination of some biogas impurities is essential to avoid high toxicity, for an ideal use of biogas for waste management and renewable energy production.