|Other Abstract||Reducing Carbon dioxide (CO2) emissions is a global issue. Coal is one of important sources of CO2 emissions. Coal-fired flue gas, which contains sulfur dioxideone (SO2), nitrogen oxide (NOx), soot and other harmful ingredients, aggravates the complex of the atmospheric pollution. Due to 70 % of China energy primary use is coal, it is key to abate the flue gas CO2 from burning coal.
The photosynthesis of plants is an important method of immobilization and reducing CO2. Algae are primary producers in aquatic ecosystems. It is used to absorb CO2 with high fixation rate thanks to its individual small, fast growth, rapid metabolism and other advantages. Furthermore, algae living cells is also useful to reduce heavy metals contained in filtrate of tailings.
In this study, the mixed algae selected from brackish water lake are tolerant and adaptable to salt environment. Environmental factors such as light, salinity, calcium were observed on algae growth and CO2 fixation rate. Based on the optimum cultured for algae, two algae bioreactors were further built to fix coal-fired flue gas CO2, SO2, NOx and to reduce heavy metals in filtrate of tailings, respectively. We explore the mechanism of algae fixing CO2 from burning coal and reducing heavy metals in tailings in order to contribute to theoretical information for cutting these pollutants of air and water.
Results of environmental factors indicated that the mixed algae can growth rapid, biomass and chlorophyll content eventually reached a maximum of 32.75 g·L-1 and 4.64 mg·L-1 respectively, when the light intensity was 200 μmol·m-2·s-1, and the fixation of CO2 in the air was high. The mixed algae in the salinity of 0.5 % and 1.2 % salinity grew better, especially at 1.2 % salinity. Salinity of 3.5 % inhibited the growth of the mixed algae significantly. The mixed algae can be grown in the 0 - 400 mg·L-1 range of calcium concentration. When Ca(Ⅱ) concentration was between 0 - 100 mg·L-1 , there was a positive correlation between trends in algae growth and the fixation of CO2 in the air and the calcium concentration. In summary, the environment suitable for the mixed algae growth and the fixation of CO2 in the air is 200 μmol·m-2·s-1 of light intensity, 1.2 % salinity, the calcium concentration of 100 mg·L-1.
Then, the mixed algae cultured in the above optimized environment were used to build two bioreactors. Coal combustion reactor operation results showed that the removal efficiency of the mixed algae on coal-fired flue gas CO2, SO2, NOx was well. Added 100 mg·L-1 Ca(Ⅱ) promoted on the mixed algae growth and removal of flue gas CO2, SO2, NOx, and when the flue gas containing 10 % (v/v) CO2 , removal results was the best one.
It was also shown that the mixed algae well tolerated to tailings leachate of Ca(Ⅱ) and other heavy metals, and good for total As removal capability. Due to the differences of heavy metals and Ca(Ⅱ) concentration inⅠ, Ⅱ, Ⅲ three bioreactors, by ligand complex, calcify and other effects on heavy metals removal vary. Removal of all three reactors are the best Cd and Pb (mean 91 % - 93 %), total As removal rate of all three reactors reached about 52 - 73 %.
Comprehensive analysis indicated that the mixed algae could be used in the fixation of flue gas with CO2, SO2, NOx and other gases and the removal of heavy metals in the filtrate tailings. This study highlights that that the mixed algae had a good ability to abate air pollutants and to biological repair heavy metals in waste water.|