Nitrogen oxides (NOx), a significant portion of fossil fuel flue gases, are among the most serious environmental issues in the world, particularly in present-day China. And surely the NOx need to be eliminated before emitting to the atmosphere. However, physico-chemical deNOx methods, which are the conventional NOx treatments, are expensive and produce secondary wastes that often require further treatment. Nitrogen (N), the basic element for algal production, can be metabolized by microalgae. Thus, a biological DeNOx method that uses microalgae may be a noteworthy method for flue gas treatment to reduce NOx emissions and merit further studies.   

Researchers from the Research Group of Algal Biochemistry at Institute of Hydrobiology, Chinese Academy of Sciences (IHB) evaluated the feasibility of microalgae used for Biological DeNOx of Industrial Flue Gases. By using actual flue gas fixed salts for the cultivation of algal cells, it is much more appropriate to evaluate the application of Chlorella sp. C2 for biological denox of industrial flue gases. Also, NO, the main component of NOx, is sparingly soluble in water, and the dissolution of NO into the microbial culture is the rate-limiting step for NO removal, so the fixation of actual flue gas for the cultivation of algal cells is a possible effective way of improving NO or NOx removal efficiency, and the calculation of the removal capacity could be more accurate. 

By using an oil-producing green alga Chlorella sp. C2, a 60% nitrite removal efficiency was obtained together with the production of 33% algae lipids, which may provide a new insight into the economically viable application of microalgae in the synergistic combination of biological denox of industrial flue gas and biodiesel production. Also, it is hoped that the results of the present research will provide a useful reference for the usage and environmental control of NOx using microalgae.   

The article entitled “Evaluation of an Oil-Producing Green Alga Chlorella sp. C2 for Biological DeNOx of Industrial Flue Gases” was published on Environmental Science & Technology.   

This work was supported jointly by the National Program on Key Basic Research Project, the Natural Science Foundation of Hubei Province of China, the National Natural Science Foundation of China, Sinopec, and the Knowledge Innovation Program of the Chinese Academy of Sciences.   

Figure:The diagram of biological DeNOx method by microalgae. (Image by IHB ZHANG xin)