Research On Enhanced Harvesting Of Scenedesmus Biomass By Immobilization Of Aspergillus Niger Mycelia Pellet

The high cost in the process of microalgal harvesting is one of the bottlenecks in the commercialization of microalgae.Currently,techniques for harvesting microalgal cells have been developed,including centrifugation,filtration,flotation and flocculation.However,due to the problems such as high cost and secondary pollution,new microalgal harvesting technologies are urgently needed.Fungi has the ability to adsorb algae cells by forming mycelia pellets,thus microalgal biomass could be harvested by the filtration of pellets.This new harvesting method is getting more and more attention because of its low cost and high efficiency.Therefore,this paper is devoted to the screening of filamentous fungal strains,which can form the pellets by self-flocculation and adsorb microalgal biomass.Furthermore,the paper investigated the immobilization mode,addition time and affecting factors of filamentous fungi with high adsorbtion activity,and made a preliminary exploration for the mechanism of pellet formation.The main results were shown as follows:A fungal strain,which could produce pellets by auto-flocculation,was screened from activated sludge and was named as Aspeigillus niger X-5 by identification of its morphology,physicochemical characteristics and molecular biol ogy.Stain X-5 could grow fast and form black brown villiform spores when cultured on PDA medium at 25 ?.The front side of medium presented black green,and reverse side was yellow.The mycelia had horizontal partition rather than vertical partition,and its width was 3-12 ?m.Nine carbon sources including glucose,sucrose and starch could be used by strain X-5 to produce mycelia pellets,which were harvested by simple filtration.The optimal pellets-forming conditions were sucrose of 10 g/L,ammonium chloride of 1.0 g/L,potassium hydrogen phosphate of 1.0 g/L,magnesium sulfate of 0.5 g/L,ferrous sulfate of 0.01 g/L,potassium chloride of 0.5 g/L and p H of 7.0.A lot of mycelia pellets with good adsorption performance were obtained after cultivation of 36 h,when spores were inocul ated on PDA medium and cultured in a shaker with 160 rpm at 30 ?.This work also established an effective control strategy of biomass harvesting by immobilization of pellets.The adsorption of pellets for microalgal cells is more suitable for biomass recovery.The adsorption efficiency was approximate 100%,when the addition of pellets was after 20 hours of microalgal inoculation.In addition,the effect of algal fluid p H on the mycelium pellet was investigated,and the results were found to be the best in the area of p H 6-8.And the optimum adsorption temperature of 30 ?,the best table speed of 160 rpm.Mechanical shearing force was also one of key factors for the formation of pellets,and the optimal running speed for shaker was 160 rpm,when adsorption efficiency could reach 94%.The increase or decrease of speed was not beneficial to formation of pellets and adsorption of microalgal cells,which had an negative effect on biomass harvesting.Finally,the formation of single mycelium and the formation of mixed mycelia pellet were explored.Hyphae of Aspeigillus niger X-5 type pellet formation way as the agglutination,spore condensed before after long hyphae,spore inoculation quantity and number of mycelia pellet appeared a certain ratio.Further shows that,despite the relative to the synchronous culture method,adsorption method to cultivate the hypha for micro algae adsorption was poorer,micro algae were mainly distributed in the mycelia pelletouter layer,and less number of microalgae adsorption on single hyphae.However,mold and micro algae were at the right envi ronment,so the adsorption method was more advantageous to mycelia pelletformation and micro algae growth,harvest more favorable for the substrate utilization and grease.The results of Zeta potential showed that the lower the p H for both condensed more favorable,the influence of p H on the growth is more stronger than the influence on the Zeta potential,so the p H of 6-7 was more suitable for cultivation of microalgae and mold the p H range.At the same time,in view of the material on the surface of the Aspeigillus niger analysis showed that the polysaccharide and protein on the surface of the material was an important part for its adsorption performance.