Possibility of co-culturing Euglena gracilis and Lactuca sativa L. with biogas digestate

ABSTRACT

The goal of this study was to establish a system for co-culturing microalgae and crop plants with biogas digestate. We examined growth performances of E. gracilis and L. sativa co-cultured using a commercial liquid fertilizer designed for soilless culture supplemented with vitamins and ammonium. This solution simulated the filtrate of nitrified biogas digestate derived from the organic fraction of municipal solid waste but was supplemented with insufficient plant nutrients (Mg, Fe and Mn). The specific growth rate of the co-cultured E. gracilis was 0.761 ± 0.081 d⁻¹ (mean ± SE), which was the same rate that E. gracilis achieved when grown as a sole culture. There were no significant differences between L. sativa cultured with E. gracilis until the stationary growth phase of E. gracilis was reached and those cultured alone relative to biomass, RGRs (relative growth rates), or relative to SPAD values of leaves. These results suggest that E. gracilis and L. sativa could be co-cultured with the biogas digestate after being nitrified and filtered. In addition, considering concentrations of plant macronutrients in the residual solution after the co-culturing E. gracilis and L. sativa, it could be re-used as the nutrient solution for co-culturing E. gracilis and L. sativa.

GRAPHICAL ABSTRACT

KEYWORDS:

• Co-culture
• methane fermentation
• organic fraction of municipal solid waste
• recycling
• soilless culture

Acknowledgments

The authors are grateful to Dr Masami Nakazawa and Dr Liya Xiao, Osaka Prefecture University, for supporting culturing of E. gracilis; Dr Toshio Shibuya and Dr Teruo Wada, Osaka Prefecture University, for supporting culturing of L. sativa; and Dr Takao Nakagiri and Dr Shinji Sakurai, Osaka Prefecture University, for supporting measurement of culture medium components.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Japan Society for the Promotion of Science under [grant number 15K12246 and 18H04984].