Study On Coculture Induced Self-flocculation For Harvesting Of Microalgae

With the high speed development of global economic,great demand for fossil energy and increasingly serious environmental pollution have led the researchers to look for alternative fuel.Microalgae are potential candidates for the production of biofuels owing its higher photosynthetic efficiency,quicker growth rate and shorter growth cycle,but the high-energy consumption of harvesting biomass makes current commercial microalgal biodiesel production economically unfeasible.Self-flocculation is regarded as a cost-efficient strategy for harvesting microalga.in coculture,microalgae may respond to stress conditions induced by the interaction,and they are maybe likely to induce Self-flocculating of algal cells.It is expected to obtain high lipid productivity and better fatty acid composition.In this experiment,microalgae Desmodesmus sp.ZFY and microalgae Monoraphidium sp.QLY-1 were used in co-cultured system.We studied the effects of coculture on the growth,lipid accumulation and fatty acid composition and the culture conditions were optimized.The effect of extracellular polymeric substances?EPS?on the flocculation of microalgae was revealed,and the mechanism of coculture promoting the flocculation of microalgae was preliminarily clarified.This paper provided an effective method for the efficient collection of microalgae biomass and the reduction of the production cost of microalgae biodiesel,and provided certain information for the further study of the molecular mechanism of coculture system inducing microalgae self-flocculation.The specific research results are summarized as follows:?1?A mixture of both Desmodesmus sp.ZFY:Monoramithium sp.QLY-1?1:1?with an initial cell count of 4.00×10⁶ cells mL^-1 was cultured mixotrophically.After 7 days,the lipid productivity of the coculture reached a maximum value of 93.99 mg L^-1 d^-1.Therefore,based on biomass,biomass productivity,lipid content and lipid productivity,it is suggested that coculture could be a feasible method for biofuel production.?2?The flocculation efficiency of ZFY and QLY-1 in coculture after 4 hours of natural sedimentation was 55.59%,which was higher than that in mono-culture?ZFY:38.66%,QLY-1:15.73%?.By optimizing the carbon source,nitrogen source and shearing force of the coculture,the flocculation efficiency of the coculture was improved to 82.34%,which was 48.12%higher than that before the optimization.?3?EPS played a key role in microalgal cell aggregation.The coculture is beneficial to the accumulation of EPS.The concentrations of EPS in coculture was higher than that in mono-culture.The concentration of total EPS in coculture was368.40 mg L^-1 higher than 309.76 mg L^-1?ZFY?and 267.77 mg L^-1?QLY-1?in mono-culture,respectively.?4?In this study,data strongly indicated that LB-EPS produced under coculture conditions played an important role in the flocculation process and remarkably improved the flocculation efficiency.After added LB-EPS extracted from coculture,the flocculation efficiency was significantly increased by 66.99%and 135.52%,respectively.The concentration of polysaccharides in LB-EPS was 46.53%in coculture,far higher than that in mono-culture?ZFY,27.01%and QLY-1,27.35%?.Increasing the polysaccharide fraction in EPS would enhance the flocculation efficiency and induce self-flocculation of algae cells.