Selection of microalgae suitable for culturing with digestate from methane fermentation

Abstract

The effects of digestate on the growth rates of Euglena gracilis, Chlorella vulgaris, and Dunaliella tertiolecta were investigated to select suitable microalgae for culturing with digestate from methane fermentation. Microalgae were cultured in an aqueous solution containing digestate at concentrations of 5%, 10%, 13%, 20%, 40%, 50%, and 100%, and Cramer–Myers (CM) solution as a control, at photosynthetic photon flux densities (PPFDs) of 75–150 μmol m⁻² s⁻¹ with continuous illumination at 30°C. The number of cells was monitored daily, and specific growth rates (μ) were calculated as cellular multiplication rates. The maximum μ values of these species were greater in appropriate concentrations of digestate than in CM medium. The maximum μ values were 0.047 h⁻¹ in 10% digestate for E. gracilis, 0.065 h⁻¹ in 20% digestate for C. vulgaris, and 0.052 h⁻¹ in 50% digestate for D. tertiolecta at a PPFD of 150 μmol m⁻² s⁻¹. The μ of D. tertiolecta were 2.5 and 1.1 times higher than those of E. gracilis and C. vulgaris, respectively, in 50% digestate. These results demonstrated that these species could be cultured at high growth rates with diluted methane fermentation sludge and that, among these species, Dunaliella sp. was suitable for culturing at higher concentration of digestate under relatively low-level light conditions.

Keywords:

• Chlorella
• Dunaliella
• digestate
• Euglena
• microalgae

Acknowledgments

The authors are grateful to Dr Masami Nakazawa and Dr Vu Ngoc Ut (Can Tho University, Vietnam) for supplying microalgae and for experimental advice.