Biomass fuels are considered 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, reduce damage to the environment, achieve a zero carbon footprint, and enhance the use of the wastes of agricultural production. However, a problem in biomass power plants is the ash and flue gas (mainly consisting of CO₂ and nitrogen oxides (NOx)) generated during biomass combustion for electric power generation, which can contaminate ecosystems and should be further treatment before safe discharge.    

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. 

Researchers previously studied the feasibility and action mechanism of coupling Chlorella based production of microalgae-based lipids with the efficient biological DeNOx of flue gas (Environ Sci Technol 2014, 48: 10497-10504; Environ Sci Technol 2016, 50: 1620-1627; Appl Environ Microbiol 2017, 83: e02952-16) as well as the C/N metabolic balance during lipids production (Biotechnol Biofuels 2017, 10: 153). In this study, researchers 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 NOx present in the flue gas and sequestered CO₂, with a NOx reduction (DeNOx) 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 firstly.   

The prominent NOx 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 study was done by CHEN Hui et al., and WANG Qiang is the corresponding author. This work was supported jointly by the National Natural Science Foundation of China (31770128, 31700107), Hubei Provincial Natural Science Foundation of China (2017CFA021), the State Key Laboratory of Freshwater Ecology and Biotechnology (Y11901-1-F01), and the Science and Technology Service Network Initiative of the CAS (KFJ-SWSTS-163).  

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