Optimization Of Microalgal Culture Conditions For High Effective Utilization Of Ammonium-N And Inorganic Carbon Sources And Its Application Research

Microalgae has broad application prospects in energy,food and medicine,environmental protection and other fields.Considering the problems of high production cost,low utilization efficiency of nutrients and high energy consumption in microalgae cultivation,we conducted this study to investigate the relationship among inorganic carbon source,ammonia nitrogen and cell growth of Desmodesmus sp.F51 as well as pH change,and established a method for high efficient culture of microalgae.The proposed method was also applied to microalgae-based aquaculture wastewater treatment and lutein production.The effects of different carbon source conditions,ammonium-N and P concentrations on microalgal cell growth and N/P removal efficiency were investigated.The results show that the highest biomass productivity(335.81 mg/L/d)was obtained when the P contentration of artificial wastewater was 5-10 mg/L with a NH4'-N/P ratio of 13.3,and using a NH4+-N/NaHCO3-C ratio of 1 and 2.5%CO2.Moreover,both ammonium-N and P could be completely removed from artificial wastewater under these conditions,along with the N and P removal rate of 38.40 mg/L/d and 6.40 mg/L/d,respectively.The effects of light intensity and temperature on large-scale culture and N/P removal efficiency were investigated by using 30 L cylindrical photobioreactor.The results show that the highest biomass productivity(415.33 mg/L/d),N removal rate(33.01 mg/L/d)and P removal rate(4.93 mg/L/d)were obtained when the light intensity and temperature were 1063?mol/m2/s and 30?,respectively.Moreover,semi-continuous operation as well as outdoor cultivation was further manipulated to investigate its effect on microalgae-based wastewater treatment.The results show that semi-continuous operation was an effective strategy to maintain high cell growth rate and N/P removal efficiency under indoor or outdoor conditions.Microalgae-based semi-continuous wastewater treatment system was established to deal with real aquaculture wastewater.The results show when using this system,long term continuous cultivation of microalgae could be achieved to some extent,and also could ensure the demand for the frequent change of water in fish farming.The obtained average biomass productivity,N and P removal rate were 284.91 mg/L/d,17.32 mg/L/d and 2.98 mg/L/d,respectively.The average cell composition of the harvested algae was crude protein 628.55 mg/g,lipid 71.35 mg/g,carbohydrate 214.31 mg/g,carotenoid 8.09 mg/g and 4.41 mg/g lutein.The type and concentration of inorganic carbon and nitrogen sources were manipulated to improve cell growth and lutein productivity of Desmodesmus sp.F51.To solve the pH decline problem of ammonium consumption,the strategy of using dual carbon sources(NaHCO3 and CO2)was explored.A lower bicarbonate-C:ammonium-N ratio led to a lower culture pH as well as lower lutein productivity,but significantly enhanced the auto-flocculation efficiency of the microalgal cells.The highest biomass productivity(939 mg/L/d)and lutein productivity(5.22 mg/L/d)were obtained when CO2 concentration,ammonium-N concentration and bicarbonate-C/ammonium-N ratio were 2.5%,150 mg/L and 1,respectively.