High viscosity and hydrophobic property of vegetable oil and animal grease retard the microbial affinity and the penetration through the oil film. An innovative aerobic fluidized bed bioreactor was designed to promote effective partial oxidation of the fatty hydrocarbon. Biological transformation of oil and grease to hydrophilic terminal was detected with long chain fatty acids, and volatile fatty acids. Ice cream refuse was employed as a rich electron donor with high concentration of oil-COD (60% of total COD) and sugars. Three series of biochemical hydrogen potential and biochemical methane potential batch tests were conducted to evaluate the bioavailability for hydrogen and methane production by the acclimated microorganisms. With high substrate to microbial ratio at So/Xo=11 gCOD/gVSS, the mesophilic hydrogen fermentation could achieve with the yield of 1.8 mmol-H2/gCOD, but 1.3 g/L of oil/grease was remained without further degredation(35ºC). Thermophilic batch test (55ºC) was conducted with oil/grease up to 12.5 g/L. The thermophilic bacteria could utilize 90% of carbohydrate with the yield of 2.0 mmol-H2/gCOD, and only 5% of oil degradation. Then, re-inoculation of acclimated methanogenic sludge was applied to utilize the residual substrate. Methane and hydrogen production were occurred simultaneously, while the oil degradation was increased to 20%. The best biogas yield were 0.4 mmol-CH4/gCOD and 0.1mmol-H2/gCOD.
Syntrophic community of hydrogen-producing bacteria and methanogenes was identified with molecular biomonitoring of terminal restriction fragment length polymorphism(TRFLP) analysis and DGGE analysis. Clostridium species and Methanosarcina or Methanoseata species were recognized.