Acetate synthesis from h₂/co₂ in simulated and actual landfill samples

To investigate the characteristics of biological decomposition in a municipal solid waste landfill, laboratory simulated samples and full-scale actual samples excavated from landfills in Taiwan were used. Nitrogen gas was produced continuously in the simulated samples. Although nitrate or nitrite could not be detected in the leachate, this did not indicate that nitrate or nitrite was not available in the solid waste. Landfills both produce and consume H₂ under anaerobic conditions. In the suspension experiment, where H₂/CO₂ were used as substrate, significant acetate concentration accumulated concomitantly along with hydrogen consumption. Relatively low production of methane was observed in both the simulated sample and actual samples. Collectively, acetate synthesis was the dominant reaction in the simulated sample and actual samples for hydrogen consumption. This study was the first paper reporting that the homoacetogenesis was the significant process in the landfill for hydrogen utilization, which was validated by the consumption of 4.01–5.43 moles of hydrogen per mole acetate formed. The significant acetate accumulation indicated that the homoacetogens outcompeted the hydrogentrophic methanogens in the landfill samples. Metabolically versatile homoacetogens can use many more substrates simultaneously than their competitor which is bound only to a very few substrates. The metabolic versatility of homoacetogens could be the main reason for their success in the landfill.