H2 is a CO2 free energy carrier that can be produced biologically through dark fermentation using specific bacteria. In general, biological production of H2 needs a carbon source and is more efficient at higher temperatures. Mature petroleum reservoirs have the required high temperatures for H2 production, and they contain a significant amount of organic matter in form of residual hydrocarbons. In this work, we evaluated whether indigenous microorganisms isolated from hydrocarbon reservoirs are able to biorefine hydrocarbons to H2. We observed that two Thermotoga strains, Pseudothermotoga hypogea DSM-11164 and Pseudothermotoga elfii DSM-9442, are able to convert hydrocarbons to H2. DSM 9442 produced 0.47 and 1.02 mmol H2 per liter of growth medium from 20 ml/L of n-hexadecane or a crude oil, respectively. DSM 11164 only produced H2 from n-hexadecane (0.94 mmol/L). Addition of 25 mg/L Tween 80, to reduce phase separation, together with 1 g/L glucose increased H2 production from hydrocarbons up to 12-fold. Via an energy analysis we show that bioconversion of crude oil into H2 can be more efficient than conversion of crude oil to gasoline. Therefore, we suggest dark fermentation as a promising alternative to biorefine crude oil and unlock the energy trapped in hydrocarbon reservoirs after abandonment.
- Hydrocarbon reservoirs
- Dark fermentation