Biogenic hydrogen and methane production from Chlorella vulgaris and Dunaliella tertiolecta biomass

BACKGROUND: Microalgae are a promising feedstock for biofuel and bioenergy production due to their high photosynthetic efficiencies, high growth rates and no need for external organic carbon supply. In this study, utilization of Chlorella vulgaris (a fresh water microalga) and Dunaliella tertiolecta (a marine microalga) biomass was tested as a feedstock for anaerobic H(2 )and CH(4 )production. RESULTS: Anaerobic serum bottle assays were conducted at 37°C with enrichment cultures derived from municipal anaerobic digester sludge. Low levels of H(2 )were produced by anaerobic enrichment cultures, but H(2 )was subsequently consumed even in the presence of 2-bromoethanesulfonic acid, an inhibitor of methanogens. Without inoculation, algal biomass still produced H(2 )due to the activities of satellite bacteria associated with algal cultures. CH(4 )was produced from both types of biomass with anaerobic enrichments. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling indicated the presence of H(2)-producing and H(2)-consuming bacteria in the anaerobic enrichment cultures and the presence of H(2)-producing bacteria among the satellite bacteria in both sources of algal biomass. CONCLUSIONS: H(2 )production by the satellite bacteria was comparable from D. tertiolecta (12.6 ml H(2)/g volatile solids (VS)) and from C. vulgaris (10.8 ml H(2)/g VS), whereas CH(4 )production was significantly higher from C. vulgaris (286 ml/g VS) than from D. tertiolecta (24 ml/g VS). The high salinity of the D. tertiolecta slurry, prohibitive to methanogens, was the probable reason for lower CH(4 )production.