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

Abstract

BackgroundMicroalgae 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 H2 and CH4 production.ResultsAnaerobic serum bottle assays were conducted at 37°C with enrichment cultures derived from municipal anaerobic digester sludge. Low levels of H2 were produced by anaerobic enrichment cultures, but H2 was subsequently consumed even in the presence of 2-bromoethanesulfonic acid, an inhibitor of methanogens. Without inoculation, algal biomass still produced H2 due to the activities of satellite bacteria associated with algal cultures. CH4 was produced from both types of biomass with anaerobic enrichments. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling indicated the presence of H2-producing and H2-consuming bacteria in the anaerobic enrichment cultures and the presence of H2-producing bacteria among the satellite bacteria in both sources of algal biomass.ConclusionsH2 production by the satellite bacteria was comparable from D. tertiolecta (12.6 ml H2/g volatile solids (VS)) and from C. vulgaris (10.8 ml H2/g VS), whereas CH4 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 CH4 production.

Comparative testing of energy yields from micro-algal biomass cultures processed via anaerobic digestion

“…Biogas composition was analysed each time the collection cylinder was emptied. The methane content of the sample was measured by gas chromatography, using a Varian star 3400 CX Chromatograph with a mixed gas standard of 65% CH 4 …”

“…In practice, however, serious issues may be encountered in long-term continuous digestion processes. Micro-algae from marine environments are likely to cause difficulties associated not only with high salinity but also with high sulphate concentrations [4,25]. To date most micro-algae that have been tested for digestion have low carbon/nitrogen ratios that may contribute to high digester ammonia concentrations and toxicity [26].…”

“…Other research approaches have considered the production of hydrogen through biophotolysis [2,3] and, more recently, by indirect photolysis and dark fermentation [4]. The potential for direct ethanol production appears limited, although the fermentation of starch storage products may be more favourable [5].…”

Effect of co-substrate feeding on methane yield of anaerobic digestion of Chlorella vulgaris

“…Microalgal production offers many advantages over the use of terrestrial plants, because microalgae have higher photosynthetic efficiencies and higher biomass yields, and non-conventional rural areas can be used for algal cultivation (Adenle et al 2013;Mussgnug et al 2010). The main energetic use of algal biomass can be highly variable; it is regarded as the source of gaseous (methane and biohydrogen) and liquid biofuels (biodiesel, ethanol, and butanol) (Amin 2009;Lakaniemi et al 2011). In the case of nonpretreated microalgal biomass, the highest-energy yield with methanogenic digestion is very close to the value obtained for ethanol production (Lakaniemi et al 2011).…”

“…The main energetic use of algal biomass can be highly variable; it is regarded as the source of gaseous (methane and biohydrogen) and liquid biofuels (biodiesel, ethanol, and butanol) (Amin 2009;Lakaniemi et al 2011). In the case of nonpretreated microalgal biomass, the highest-energy yield with methanogenic digestion is very close to the value obtained for ethanol production (Lakaniemi et al 2011). The anaerobic digestion (AD) process of algal biomass of low lipid content produces a significantly larger amount of energy compared with biodiesel alone (Bohutskyi et al 2014b).…”