Research On Adaptability And Adjustment Of Botryococcus Braunii In Wastes

With the rapid consumption of fossil fuels and its increasingly serious greenhouse effect, governments attach great importance to the development of bioenergy. Microalgae are a group of unicellular or simple multicellular photosynthetic microorganisms that can fix CO2 efficiently. In recent years, microalgae have attracted more attention for the possibility of being exploited as a renewable source of fuels, whereas its commercial development has been prevented by economic problems. To lower the cost of microalgal biofuels production, the potential of using 2-20% CO2, bamboo industrial wastewater and swine lagoon wastewate to cultivate Botryococcus braunii were investigated. The results were as following:(1) A photobioreactor was successfully established, with several advantages, such as lower price, easily control and stable operation characteristics. In addition, a novel method using sodium hypochlorite solution was successfully utilized for the photobioreactor sterilization.(2) B. braunii 765 could grow well without any obvious inhibition under all tested 2-20% CO2 concentrations with an aeration rate of 0.2 vvm, even without any culture pH adjustment (ranged from 6.0 to 8.0). The maximum biomass among all conditions was 2.31 g/L on 25th day at 20% CO2. Hydrocarbon content and algal colony size increased with the increase of CO2 concentration. A negative correlation between algal biomass and culture total phosphorus was observed (from-0.828 to-0.911, P< 0.01). NaHCO3 could be used by B. braunii 765 as carbon source. In addition, if there was 5 g/L glucose in BG11 medium, the growth rate of B. braunii 765 could be greatly increased when the strain was in light instead of darkness.(3) On day 0-12 after inoculation, B. braunii grew well in the bamboo industrial wastewater. And both the growth rate and hydrocarbon content of the algae were higher than those grown in BG11 medium (control) during this period. After 8 days from inoculation, the algal colony density and hydrocarbon content in bamboo industrial wastewater reached 1.92 and 1.98 times of the control. During the same period, no contamination by other algae species was detected in the system. On day 12-24 after inoculation, the growth of B. braunii in bamboo industrial wastewater was obviously inhibited and some Chlorella sp. and rotifers in the wastewater were found. In addition,70.6% total nitrogen,66.1% nitrate and 74.0% total phosphorus in the wastewater were removed when the alga density in it reached the highest point.(4) The alga strain could maintain a competitive advantage over the 26-day cultivation in swine lagoon wastewater. The highest dry biomass of alga grown in the wastewater was 0.94 mg L-1 at day 24, which was 1.73 times that grown in BG11 medium. And the algal hydrocarbon content was 23.8%, more than twice that in BG11 medium. Additionally, about 93.7% and 98.6% of TN and TP in the wastewater were removed, suggesting that environmental benefit for the alga.In summary, CO2 from flue gas and aerated-swine-lagoon-wastewater could replace chemical carbon and nutrients in B. braunii artificial cultivation, respectively. The culture of microalgae using flue gas and wastewater would benefit both microalgal biofuls production and environment protection.