Current status and prospect of carbon fixation and emission reduction technology for coal-fired flue gas by microalgae

The flue gases emitted from coal-fired power plants containing various pollutants such as CO2,SOx,NOx and heavy metals, which significantly affects the atmospheric environment. Traditional technologies of flue gas treatment include smoke and dust control, flue gas desulfurization and denitrification,etc. Such processes are restricted by problems such as complicated process equipment, high energy consumption, high treatment costs and heavy secondary pollution. Compared with the traditional coal-fired power plant flue gas emission reduction technology,carbon fixation and emission reduction by microalgae is considered as a promising technology due to the advantages of simple process equipment, convenient operation and environmental protection. When the flue gas is treated by the technology of carbon fixation and emission reduction by microalgae, microalgae cells can fix CO2 in the flue gas through photosynthesis, and simultaneously absorb NOx and SOx as nitrogen and sulfur sources required for growth. Meanwhile, they can also absorb heavy metal ions (Hg, Se, As, Cd, Pb, etc.) in the flue gas to obtain microalgae biomass,which can be further converted into biodiesel, ethanol, methane and other high value-added products, which has broad development prospects. In this paper, the mechanisms and pathways of dissolution, transport and conversion of coal-fired flue gas pollutants such as CO2, NOx and SOx in the microalgal culture system were comprehensively analyzed, and the mechanism of microalgal emission reduction of flue gas pollutants and the impacts of flue gas pollutants on microalgal growth were also systematically discussed. Based on the effects of the composition of the flue gas, the photobioreactor structure and the gas-liquid mass transfer characteristics on the growth of carbon fixation and emission reduction of microalgae, the advances and challenges of microalgae selection, photobioreactor and aeration methods were reviewed. The progress and existing problems, and the principles and methods of enhancing the growth of microalgae and the removal of flue gas pollutants are discussed. An integrating system of the carbon dioxide emission reduction and biomass recovery of microalgae gas based on the comprehensive utilization of waste heat and pressure of coal-fired power plants are proposed.The integrated system provides some guidelines for the research and application of green emission reduction technology for coal-fired power plants.