Study On Citrobacter W4 Harvest Chlorella Process And Its Mechanism

The production of biodiesel from microalgae cultured in municipal sewage can realize the recycling of sewage,which is one of the solutions to the energy crisis and environmental pollution.However,microalgae harvesting has become a major bottleneck in the industrialization of microalgae biodiesel process.Although there have been a lot of researches on microalgae harvesting methods,none of them has been industrialized.In the early stage,Citrobacter W4 was screened from microalgae sewage culture system,and performed?92.38±1.57?%flocculating efficiency against Chlorella in laboratory.Based on the previous research,this paper discussed the reasons why Citrobacter W4could performed flocculation against Chlorella,explored the flocculation conditions of Citrobacter W4 against Chlorella under outdoor conditions,and analyzed the economic feasibility of this process.The reasons of Citrobacter W4 performed flocculation against Chlorella were discussed.The results showed that Citrobacter W4 could adapt to the Chlorella sewage culture system,become the dominant strain and play a flocculating role.Further analysis of flocculating active substances produced by Citrobacter W4 and flocculating mechanism was carried out.It was found that there were flocculating active substances on the cells and metabolites of Citrobacter W4.The main components of flocculating active substances were protein,polysaccharide and carboxylic acid.And active groups such as amino and carboxyl groups played an important role in flocculation.The flocculation mechanism was mainly adsorption bridging,net catching and sweeping,and had nothing to do with electric neutralization.By exploring the flocculation conditions of Citrobacter W4 against Chlorella process under outdoor conditions,the optimal harvesting parameters were obtained:the harvest time was 6 h,the bacteria-algae ratio was 4:1,and the mixing speed gradient G value was 26.30 s^-1.The optimum microalgae harvesting efficiency under these conditions was?87.37±2.96?%.By analyzing the influence of Citrobacter W4 harvesting process on subsequent processed,it was found that the effluent quality was effected,and the addition method of Citrobacter W4 should be improved.By comparing the changes of oil yield before and after harvesting,it was found that the oil yield were not significantly affected by Citrobacter W4 harvesting process.In addition,the quality of microalgae biodiesel could be improved after the harvesting by Citrobacter W4.The economic feasibility analysis of the process of Citrobacter W4harvesting Chlorella showed that the cost of this process under parameters of small trial scale was 10.24 yuan/kg dried algae powder,equivalent to 1.49$/kg dried algae powder,which was superior to other harvesting methods,but there was still a gap with the crude oil price on the market.In the following studies,further studies can be carried out from the aspects of optimizing flocculation conditions,improving the adding mode of Citrobacter W4 and optimizing the culture conditions of Citrobacter W4,so as to further propel the industrialization of microalgae biodiesel process.