| Recently,with the rapid consumption of oil resources,the environment has deteriorated seriously.The research and development of biomass energy is a hot spot.It is an inevitable trend for the sustainable development of society and economy to replace fossil energy with biodiesel.Microalgae due to high lipid content,fast growth rate and strong environmental adaptability,has become the most potential raw materials for biodiesel production.The preparation of biodiesel by microalgae includes several processes:microalgae's cultivation and harvest,and transesterification of biomass to energy.However,the characteristics of microalgae such as small size and cell density lead it difficult to be harvested,s high cost,and the high moisture content of microalgae after harvesting will also cause difficulties in oil extraction.Some studies have shown that microalgae harvesting accounts for 20–50%of the total cost of the whole biodiesel prodution.In recent years,many researches have been published about the harvesting of microalgae,but there are few reports about the effect of flocculants on the extraction of lipid and biodiesel production after harvesting of microalgae.Therefore,this paper mainly focuses on the harvesting of microalgae and lipid extraction and transesterification.Four differenet flocculants?ferric chloride,ferric sulfate,calcium hydroxide and chitosan?were selected to compare the effect on the flocculation efficiency of two lipid-rich microalgae?Chlorella vulgaris and Scenedesmus quadricauda?and the conversion of fatty acid methyl esters?FAME?.The results showed that the metal salt flocculant represented by ferric chloride had better recovery on both microalgae,and the flocculation efficiency more than 90%at low concentration of 0.3 g·L-1.According to the SEM images,the damage to algae cell structure during the harvesting process of microalgae by ferric chloride was relatively small.From the transesterification results of FAME,the content of FAME was hihger obtained by ferric chloride.The FAME content of Chlorella vulgaris?C.vulgaris?and scenedesmus quadricauda were 53.64%and 21.44%,and the conversion rates were90.92%and 89.18%,respectively.Thus,from the abobe data,It could be conclude that C.vulgaris is more suitable for biodiesel production.C.vulgaris was used as the experimental object.The effect of ferric chloride and ferric sulfate on the lipid extraction and biodiesel production were investigated.The influence of acidification on FAME conversion during flocculation processes was analyzed,and the effect of metal ions on the growth and lipid accumulation of C.vulgaris was also studied.The results showed that the optimum flocculating conditions were 0.3 g·L-1 of ferric chloride for 3 min,and the recovery was about 98%,,and much higher FAME obtained by ferric chloride flocculation proceess.The acidification process can release Fe3+from the concentrated solution and improve the conversion of FAME.The addation of ferri ion into the culture medium could promote the lipid accumulation without affecting the growth of C.vulgaris,the conversion rate of FAME was about 88.17%.Biodegradable chitosan was used as flocculant to harvest C.vulgaris,and the effect of chitosan on the transesterification of FAME was investigated.The results showed that when the pH of the culture medium was adjusted to be acidic?pH=4.0?,t90%of flocculation efficiency could obtain at the condition of 0.9 g·L-1 chitosan for20 min.According to the results of FAME transesterification,it could be conclude that lower PH medium culture could improve the FAME conversion of C.vulgaris. |
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