Biomass fuels are considered as renewable fuel sources and do not affect the overall balance of CO₂ in the atmosphere. Obtaining energy from biomass could reduce the dependency on fossil fuel and energy import, achieve a zero carbon footprint, and enhance the use of the wastes of agricultural production, which is environmental friendly.

The ash and flue gas (mainly consisting of CO₂ and nitrogen oxides (NO_x)) generated in biomass power plants during biomass combustion for electric power generation can contaminate ecosystems, and should be further treated before emission.

The Research Group of Algal Biochemistry at Institute of Hydrobiology (IHB) of Chinese Academy of Sciences confirmed that ash and flue gas produced in biomass power plants can be used as free nutrients source for Chlorella cultivation coupled biofuel production. The findings were published in Applied Energy.

The research group has studied the feasibility and action mechanism of coupling Chlorella based production of microalgae-based lipids with the efficient biological DeNO_x of flue gas as well as the C/N metabolic balance during lipids production.

In this study, they further evaluated whether the nutrient-rich ash and flue gas generated in biomass power plants could serve as a nutrient source for Chlorella sp. C2 cultivation to produce biolipids in a cost-efficient manner.

The results showed that when ash was incorporated in the culture medium and photosynthesis was enhanced by CO₂ from flue gas, 39% and 35% more lipid productivity and biomass productivity than the control cultures grown in BG11 medium are obtained.

Additionally, the cultures reduced the NO_x present in the flue gas and sequestered CO₂, with a NO_x reduction (DeNO_x) efficiency of ∼100%, and a CO₂ sequestration rate of 0.46 g L⁻¹ d⁻¹. In the end of cultivation, a maximum ash denutrition rate of 13.33 g L⁻¹ d⁻¹ is achieved, and the residual medium was almost nutrient-free and suitable for recycling for continuous microalgal cultivation or farmland watering, or safely disposed off.

Based on the results, an economically viable technical strategy for algal biofuel production coupled bioremediation of biomass power plant waste was proposed for the first time.

The prominent NO_x removal and CO₂ sequestration rates based on Chlorella culture are achieved along with considerable lipid productivity, indicating the economic feasibility of C negative bioenergy production with significant economic, environmental and social benefits.

This study will be of great interests not only to scientists working on industrial wastes reutilization and low-cost biofuel production, but also to industrials with demands on environment-friendly industrial wastes bioremediation.

This work was supported jointly by the National Natural Science Foundation of China, Hubei Provincial Natural Science Foundation of China, the State Key Laboratory of Freshwater Ecology and Biotechnology, and the Science and Technology Service Network Initiative of the Chinese Academy of Sciences.

Figure: A technical strategy for reusing the contaminants from biomass power plants to nourish the microalgae for algal biofuel production. (Image by IHB)