Carbonate Assisted Biodiesel Production And Carbon Capture For Recycling Cultivation Of Microalgae

Algae is one of the most promising sources of biofuels to replace petroleum,however,some technical barriers prevent it from being used in a large scale for industrial production.The current cost mainly comes from the low oil production per unit in the upstream culture,the cost of CO₂,the cost of spray drying technology in the downstream stage and the cost of treating the wastewater.Therefore,in order to solve above problems,a set of process flow based on bicarbonate from cell-wall breaking to cyclic culture was established.Firstly,in the entire system,NaHCO₃ was used instead of traditional CO₂ to supply inorganic carbon for Neochloris oleoabundans to reduce culture cost.In order to improve the yield of algae per unit volume of lipid,Plackett-Burman was used to screen the factors that have a significant effect on the growth and lipid accumulation of N.oleoabundans:ZnSO₄·7H₂O,MgSO₄·7H₂O,EDTA-2Na and Na NO₃.Central composite design was established to further explore the significant factors and the optimum condition that 0.007mM ZnSO₄·7H₂O,0.74 mM MgSO₄·7H₂O,2.88 mg/L EDTA-2Na and 3.98 mM NaNO₃ was determined.The optimum condition for the cultivation of N.oleoabundans was 1.73 g/L for dry cell weight?DCW?and 23.4%?DCW?for total fatty acid?TFA?.Secondly,lipid extraction directly used wet algae as raw materials The ionic liquid and carbonate were used to break cell-wall and ethanol/Na₂CO₃ aqueous two-phase system was used for the aqueous two-phase extraction.The optimal Na₂CO₃/H₂O?w/w?ratio of was 1:3;the optimal DBU/H₂O?w/w?was 1:7.5;the optimal reaction time was 100 min;the optimal reaction temperature was 90?;the optimal ethanol concentration was 9%?w/w?in the system.The partition coefficient and recovery of lipid were the highest,reaching at 96.66 and97.93%,respectively.At the same time,in the ethanol/Na₂CO₃ aqueous two-phase system,pigments and protein also had high recoveries.The extraction rate of N.oleoabundans by our method was 1.3 times higher than that with Soxhlet method,which indicated that our method can effectively break cell-wall and extract lipid from N.oleoabundans.Finally,N.oleoabundans was cultured by adding different volume ratios of bottom phase?carbonate-containing concentrates?.It was finally found that DCW of the algae could reach1.88 g/L when adding 4%?v/v?bottom ratio and the yield per unit volume of TFA was highest?0.35 g/L?.Simultaneous addition of this volumetric ratio enabled complete recycling of the produced wastewater.